Ac Gas Recharging

[Sifaan]

A/C gas refilling, whenever I've seen it being done, has involved a thermometer in the airvent and monitoring the pressure while infusing gas into the system.

However, the "correct" way (at least for my car) appears to be to refill to a particular weight (625 +/- 25g in my case). Even the workshop manual gives the weight, not the pressure.

Of course, even if you measured the gas going in, this would only work if you knew how much gas there was in the car, which supposedly involves extracting all the gas using some machine, and then refilling. apparently there's some loss in this process, but generally speaking you'd pay only for the additional gas used (apart from labour charges, etc.)

I guess this system would also really make sense for certain kind of repairs (where otherwise all the gas would be lost).

anyway, my question is - does anyone know of any places that have the machine to do this?

[jdnet]

anyway, my question is - does anyone know of any places that have the machine to do this?

Lots. Actually any decent place that does A/C repairs will have a machine to evacuate and store the freon. Don't know much about A/C work other than using refill kits so I couldn't tell you how you would go about with weighing the thing.

[The Don]

A/C gas refilling, whenever I've seen it being done, has involved a thermometer in the airvent and monitoring the pressure while infusing gas into the system.

However, the "correct" way (at least for my car) appears to be to refill to a particular weight (625 +/- 25g in my case). Even the workshop manual gives the weight, not the pressure.

Of course, even if you measured the gas going in, this would only work if you knew how much gas there was in the car, which supposedly involves extracting all the gas using some machine, and then refilling. apparently there's some loss in this process, but generally speaking you'd pay only for the additional gas used (apart from labour charges, etc.)

I guess this system would also really make sense for certain kind of repairs (where otherwise all the gas would be lost).

anyway, my question is - does anyone know of any places that have the machine to do this?

Sifaan, though I haven't seen this approach used, I can see it being done quite easily by simply suspending the gas cylinder from a weighing scale. You would have to flush and vacuum the system entirely for this to work though (or you can flush the gas out store it and re use it should I would not recommend that).

Having said that I think the standard method might be preferred anyway, because sometimes in SL you have to pressurise the car less than manufacturer specifications to achieve consistent cooling thanks to our ambient environmental temperature. You pressure it up to spec and the pressure cut off kicks in too early leaving you with inefficient cooling (this is because warm gas is harder to compress and the pressure internally increases as the gas warms and expands, so our guys pump a little less gas to compensate for this). This obviously relies a lot on experience.

What is your car by the way? Sounds European

[Sifaan]

Lots. Actually any decent place that does A/C repairs will have a machine to evacuate and store the freon. Don't know much about A/C work other than using refill kits so I couldn't tell you how you would go about with weighing the thing.

called up a few places, one place said they don't have the machine because it's too expensive; another place has the machine but they no longer use it because they had problems because of reusing the evacuated gas; so they just release any existing refrigerant and then pump fresh (but they did say they could sell by the weight)

I can see it being done quite easily by simply suspending the gas cylinder from a weighing scale. You would have to flush and vacuum the system entirely for this to work though (or you can flush the gas out store it and re use it should I would not recommend that).

why do you not recommend reusing refrigerant?

Having said that I think the standard method might be preferred anyway, because sometimes in SL you have to pressurise the car less than manufacturer specifications to achieve consistent cooling thanks to our ambient environmental temperature. You pressure it up to spec and the pressure cut off kicks in too early leaving you with inefficient cooling (this is because warm gas is harder to compress and the pressure internally increases as the gas warms and expands, so our guys pump a little less gas to compensate for this). This obviously relies a lot on experience.

Interesting take on it, but I'm now even more confused. Isn't the pressure cut off a safety thing, with the regular compressor cut off being managed by temperature sensors? to quote my online-translated french PDF (a training manual):

Safety pressure refrigeration

If too low or too high pressure in the circuit refrigeration, BSI prohibits the engagement of the compressor refrigeration.

This strategy helps guard against events following:

Low pressure: risk of leakage of refrigerant circuit,

pressure too high: the risk of deterioration of the circuit refrigeration.

What is your car by the way? Sounds European

Citroen C5, 1st gen

[The Don]

called up a few places, one place said they don't have the machine because it's too expensive; another place has the machine but they no longer use it because they had problems because of reusing the evacuated gas; so they just release any existing refrigerant and then pump fresh (but they did say they could sell by the weight)

why do you not recommend reusing refrigerant?

Interesting take on it, but I'm now even more confused. Isn't the pressure cut off a safety thing, with the regular compressor cut off being managed by temperature sensors? to quote my online-translated french PDF (a training manual):

Citroen C5, 1st gen

Sifaan, the temperature sensors control the engagement and the disengagement of the compressor, but so does the pressure cut off. You are correct it is for safety, but when this kicks in the compressor disengages (for safety) leaving you with no cooling. Especially with non tropicalised vehicles this is sometimes a problem. They have condensers too small to properly cool the coolant down before re compression.

I'll be 100% honest, I've been told by my normal AC guy that he only uses reclaimed refrigerant for flushing though he did not elaborate why. I think it might be because refrigerant becomes contaminated in SL (condensation etc because the driers are never replaced) so they don't see it fit to be reused. Also another thing to consider is if you need regular top ups you probably have a leak somewhere and you are losing lubricant as well as refrigerant. If you lose too much lubricant the compressor will cease up. So it's better to fix the leak, replace the lubricant and the refrigerant as part of your usual service cycle.

[Sifaan]

I'll be 100% honest, I've been told by my normal AC guy that he only uses reclaimed refrigerant for flushing though he did not elaborate why. I think it might be because refrigerant becomes contaminated in SL (condensation etc because the driers are never replaced) so they don't see it fit to be reused.

well, seems consistent with what the A/C place that has (but no longer uses) the machine said. and can you post / PM the contacts of this guy?

do dryers need to be replaced at a certain interval? I take it they are not replaced in Sri Lanka but they are replaced in UK??

Also another thing to consider is if you need regular top ups you probably have a leak somewhere and you are losing lubricant as well as refrigerant. If you lose too much lubricant the compressor will cease up. So it's better to fix the leak, replace the lubricant and the refrigerant as part of your usual service cycle.

well... ~8 months ago, the clutch on the AC compressor was replaced (it was not engaging at all), and after that A/C worked fine but after 2-3 weeks cooling was pretty much non-existent. Took it to the place that fixed the compressor and they said the gas was low; topped it up and it worked great. (decided not to go down the test-for-leak-with-nitrogen route at that time)

I can't remember the exact value, but I think they said 200-250 was the pressure they aimed for on the high side.

Around 2 months ago A/C again wasn't working too well, so thought I'd check the pressure when I took it in for service (@Frontier), but it was about 250 (kPA?PSI) and they said pressure was fine; at that time checked the pollen filter and it was really dirty. Replaced the filter about a week later and things were good for a while again, and now again giving problems.

So I'm not entirely sure if there is a leak (how did it hold @ 250 for ~6 months and then leak in 1?). At the time I felt that it was the dirty filter that was causing the poor performance.

Is it possible for refrigerant to leak if the covers on the valves they fit the gauges on to are not closed properly?

one advantage of an evacuation machine is that it will tell me pretty accurately how much gas was in the system; and before doing that I'll check the pressure as well - if it's dropped below 250 then it means the leak happened recently (I think). If it hasn't dropped - the weight from the evacuator should prove to be interesting reading

edit: the compressor safety cutoff on the C5 is 27 bar (~390 PSI) and it will cut-in again only when pressure drops below 20 bar (~290 PSI), so that really shouldn't be kicking in normal operating conditions (~250 PSI).

Edited June 17, 2011 by Sifaan

[Sifaan]

Update - took the car in to Frontier as they have the evacuation machine. hooked up pressure gauges to the AC system and...

there is a residual pressure of about 150 PSI; when the car is first started up, pressure rises to 250-270 range, then reduces gradually until ~200 PSI. If we switch off the engine and restart, pressure again rises to 250ish and then reduces.

The diagnosis from Frontier is that there is a problem with the compressor. It might be worthwhile to remove the compressor and oil it (this seems to somehow be different from oiling in the refrigerant line) but they are not sure if that would solve the problem. Also the labour charge for doing that (evacuate gas, remove compressor, regas) might be wasted if it turns out that there is a problem in the compressor. So they recommend to take it to a garage specializing in ACs (and who could also fix the compressor once they remove it, in case that is a viable option).

Presumably what has been happening is that the duration the compressor "holds" has been reducing over the last few months, and perhaps we haven't really noticed it as most of our driving is short runs. Even when checked about 2 months ago, it probably held long enough @ 250 for us to think the gas pressure was OK (and besides, we were looking to see if the gas pressure was there, not if the compressor was able to sustain the pressure).

Assuming it is a problem with the compressor, is it worthwhile investigating the repair option or am I going to have less brain damage with a replacement?

[The Don]

Update - took the car in to Frontier as they have the evacuation machine. hooked up pressure gauges to the AC system and...

there is a residual pressure of about 150 PSI; when the car is first started up, pressure rises to 250-270 range, then reduces gradually until ~200 PSI. If we switch off the engine and restart, pressure again rises to 250ish and then reduces.

The diagnosis from Frontier is that there is a problem with the compressor. It might be worthwhile to remove the compressor and oil it (this seems to somehow be different from oiling in the refrigerant line) but they are not sure if that would solve the problem. Also the labour charge for doing that (evacuate gas, remove compressor, regas) might be wasted if it turns out that there is a problem in the compressor. So they recommend to take it to a garage specializing in ACs (and who could also fix the compressor once they remove it, in case that is a viable option).

Presumably what has been happening is that the duration the compressor "holds" has been reducing over the last few months, and perhaps we haven't really noticed it as most of our driving is short runs. Even when checked about 2 months ago, it probably held long enough @ 250 for us to think the gas pressure was OK (and besides, we were looking to see if the gas pressure was there, not if the compressor was able to sustain the pressure).

Assuming it is a problem with the compressor, is it worthwhile investigating the repair option or am I going to have less brain damage with a replacement?

Sifaan, personally I would first find out the cost of a replacement compressor, and then do whatever is more economically viable. In my personal experience I have found replacement to be more cost effective as well as more effective a solution. Because you have to factor in time, effort and the cost of re servicing the AC which has risen quite a bit.

Your diagnosis seems to make sense. I wonder why the pressure drops mid operation though. I assume this is a rotary compressor ?

[Sifaan]

Sifaan, personally I would first find out the cost of a replacement compressor, and then do whatever is more economically viable. In my personal experience I have found replacement to be more cost effective as well as more effective a solution. Because you have to factor in time, effort and the cost of re servicing the AC which has risen quite a bit.

Your diagnosis seems to make sense. I wonder why the pressure drops mid operation though. I assume this is a rotary compressor ?

well, it's a Sanden SD7V16 compressor (*) so I guess it shouldn't be too hard to track down a replacement.

(the numbers supposedly mean 7=cylinders, V= vertical mount 1=1" fittings 6= 6 groves in pulley)

According to Sanden website, this is a "Variable Displacement Piston Type" compressor

the guy at Frontier said the problem is similar to when engines develop undercompression.

(*) Either the 1211 or 1242 model (as yet not sure which - could also be that 1242 is the compressor only while 1211 includes the clutch and pulley mounting). Edit - on the compressor it says model 1242

Edited June 21, 2011 by Sifaan

[The Don]

well, it's a Sanden SD7V16 compressor (*) so I guess it shouldn't be too hard to track down a replacement.

(the numbers supposedly mean 7=cylinders, V= vertical mount 1=1" fittings 6= 6 groves in pulley)

According to Sanden website, this is a "Variable Displacement Piston Type" compressor

the guy at Frontier said the problem is similar to when engines develop undercompression.

(*) Either the 1211 or 1242 model (as yet not sure which - could also be that 1242 is the compressor only while 1211 includes the clutch and pulley mounting)

Well I had a look and seems it's widely used in VW vehicles as well as Peugeot/ Citroen. Plenty on Ebay and seems to cost around £100 for a used one. Used ones shouldn't be a problem since AC's rarely gets used in Europe. You might even find a brand new on in SL as Sander is imported I believe.

Let me know if you have any problems locating one as I can probably source one for you if you need and ship it to SL.

[Sifaan]

Well I had a look and seems it's widely used in VW vehicles as well as Peugeot/ Citroen. Plenty on Ebay and seems to cost around £100 for a used one. Used ones shouldn't be a problem since AC's rarely gets used in Europe. You might even find a brand new on in SL as Sander is imported I believe.

Let me know if you have any problems locating one as I can probably source one for you if you need and ship it to SL.

thanks for the offer Don; let's see what the AC folks say tomorrow...

[MadMMX]

Hi Sifaan,

Just to add, generally its a good thing to service - ie evacuate and regas the a/c system once a year or once in two years. You would replace the dryer when doing this. The general opinion of the a/c fellows is that at a certain point the silica gel in the dryer gets saturated with the refrigerant oil and becomes non effective over time. Have seen this first hand when I recently serviced the bmw a/c. One good option which I did is re-gas the system with R134 and UV coloured refrigerant oil. That way if there is a leak you need a black led torch and a pair of uv glasses and you can definitively find the leak. Easier than using a sniffer. Found a good chap close to pepiliyana who serviced my BM, replaced the cooler in my bro's BM and now has serviced a no of my friends BMW's. Decent fellow and quite economical and knowledgeable. PM me - can pass on the contact of you want. Got down the Behr dryer quite cheap from the US but the dryer's here are generally 2-3k so not a major cost. Had a look at the one that was pulled from my car and surely it was sorta very oily looking and dripping oil. The BMW TIS (tech cd) also recommends the use of UV refrigerant oil so no issues there and the oil is imported only by a couple of fellows from USA. Total cost for the servicing and gassing was about 5K which also included removing the condenser and giving it a good pressure clean, pulling the compressor out and giving it a good clean and re-oiling, so was very happy with the result.

Cheers,

MadMMx

[Sifaan]

Just to add, generally its a good thing to service - ie evacuate and regas the a/c system once a year or once in two years. You would replace the dryer when doing this. The general opinion of the a/c fellows is that at a certain point the silica gel in the dryer gets saturated with the refrigerant oil and becomes non effective over time. Have seen this first hand when I recently serviced the bmw a/c. ...

Had a look at the one that was pulled from my car and surely it was sorta very oily looking and dripping oil.

interesting about replacing the dryer; I'm in touch with a mechanic at a citroen dealership in australia, and he says in 10 years of working with citroen's he's only replaced the dryer twice. of course, their usage (only summer?) may be less than ours and that maybe has a bearing.

Or could it be that whenever oil is added locally (together with gas recharge) it is a hit and miss measurement (since most people don't seem to have/use an evacuator) and the system ends up with too much oil?

BTW in case anyone is interested in servicing AC compressors, found a Sanden service manual here

[MadMMX]

interesting about replacing the dryer; I'm in touch with a mechanic at a citroen dealership in australia, and he says in 10 years of working with citroen's he's only replaced the dryer twice. of course, their usage (only summer?) may be less than ours and that maybe has a bearing.

Or could it be that whenever oil is added locally (together with gas recharge) it is a hit and miss measurement (since most people don't seem to have/use an evacuator) and the system ends up with too much oil?

BTW in case anyone is interested in servicing AC compressors, found a Sanden service manual here

I do agree it is strange but the BMW TIS also recommends that if the A/C system is leaking over a few days to replace the dryer. Essentially its just a big can of silica gel by the looks of it so it would be correct in that silica can only absorb so much moisture I guess.

[The Don]

MadMMx, post the details on the forum. I keep repeating this over and over, if it's somebody good you have experience with just post the details It will help everybody !

[Sifaan]

AC folks looked at the compressor and said it has to be replaced. maybe if someone else looked at it they might be willing to attempt a repair, but I'm disinclined to pursue that. now it's a case of sourcing a compressor locally or from abroad...

one good thing about these AC dudes is that they work quite closely with frontier (on landrover more than citroen of course) but have said they'd want to use the diagnostics kit at frontier when installing a replacement (since I may still have a problem with the mixing flaps and the diagnostics can read those out).

[MadMMX]

AC folks looked at the compressor and said it has to be replaced. maybe if someone else looked at it they might be willing to attempt a repair, but I'm disinclined to pursue that. now it's a case of sourcing a compressor locally or from abroad...

one good thing about these AC dudes is that they work quite closely with frontier (on landrover more than citroen of course) but have said they'd want to use the diagnostics kit at frontier when installing a replacement (since I may still have a problem with the mixing flaps and the diagnostics can read those out).

Hi sifaan,

Sorry to hear that - but sometimes its better to bite the bullet and replace and save yourself from hassle later. Strange that the compressor was Sanden, a lot of the german cars still use only Denso and Calsonic (the bm's use only those as original equipment really) and Behr produce all the condensors, dryers and evaporators. Actually its true that you need the diags to check out the system - the diags in the bmw will tell you the internal pressure, flap positions, motor conditions ..etc and its easy to diagnose with all the information.

For all you wanting to pump in the UV dyed refrigerant, the guys name is Sudesh. Phone no is - 0773 595 971. You can call him and get directions to his place - fairly easy to find.

Cheers,

MadMMx

[The Don]

Hi sifaan,

Sorry to hear that - but sometimes its better to bite the bullet and replace and save yourself from hassle later. Strange that the compressor was Sanden, a lot of the german cars still use only Denso and Calsonic (the bm's use only those as original equipment really) and Behr produce all the condensors, dryers and evaporators. Actually its true that you need the diags to check out the system - the diags in the bmw will tell you the internal pressure, flap positions, motor conditions ..etc and its easy to diagnose with all the information.

For all you wanting to pump in the UV dyed refrigerant, the guys name is Sudesh. Phone no is - 0773 595 971. You can call him and get directions to his place - fairly easy to find.

Cheers,

MadMMx

Thanks for posting the details. I've noticed that VW use Sanden quite a lot as well.

[Sifaan]

Sorry to hear that - but sometimes its better to bite the bullet and replace and save yourself from hassle later.

would've thought I'd bitten enough bullets already - some of the suspension stuff (spheres etc.) were quite expensive to replace

Strange that the compressor was Sanden, a lot of the german cars still use only Denso and Calsonic (the bm's use only those as original equipment really) and Behr produce all the condensors, dryers and evaporators.

umm, not sure what you meant (my car is french)

Actually its true that you need the diags to check out the system - the diags in the bmw will tell you the internal pressure, flap positions, motor conditions ..etc and its easy to diagnose with all the information.

indeed - car specific diag tools open up a whole new world... I was actually positively surprised that these guys wanted to use the system because I didn't think they were that sophisticated!

I've noticed that VW use Sanden quite a lot as well.

yep, was searching on ebay US site and (almost) all the sanden compressors are for VW/Audi - but they use different model numbers than PSA so it's either local or from UK for a replacement... have so far located 5 on ebay UK ranging for 60 to 95 pounds

[MadMMX]

I was actually referring to euro cars. Actually be very careful when getting down second hand compressors. A friend of mine got down a 2nd hand compressor for his E46 from UK and while the surface looked good because the compressor had been kept uncapped for several weeks and not filled up with some ref oil so the inside was totally stuck. Fortunately Sudesh was able to take certain bits from his old compressor and couple it with the clutch and some other bits of the recon one and get it going again. He said the 2nd hand one cost him about 40 pounds from UK whereas BMW wanted 360 pounds for a genuine new one from a dealer there. Not so bad considering that Pre*t*ge wanted over 1 lakh for the compressor but even in Europe ac compressors are pricey. If you're getting down a second hand one from say uk, ask them to fill a little ref oil into it and plug the pipe paths before shipping it.

Cheers,

MadMMx

[Sifaan]

He said the 2nd hand one cost him about 40 pounds from UK whereas BMW wanted 360 pounds for a genuine new one from a dealer there. Not so bad considering that Pre*t*ge wanted over 1 lakh for the compressor but even in Europe ac compressors are pricey. If you're getting down a second hand one from say uk, ask them to fill a little ref oil into it and plug the pipe paths before shipping it.

so... update is I got down a Sanden 1242 compressor off a 2006 car (cost 46 pounds inc. postage in UK) - the seller refused to send it with oil though

when I took it to the folks who "diagnosed" that the compressor was faulty, they discovered that the gas was low (turned out there was about 250g of gas, when it should be 650-700g). they then pumped it up with nitrogen and said there was a leak but they couldn't detect where from, and so it could be the evaporator housing (which means a dashboard removal).

How they came to the conclusion that the compressor was faulty when the gas was indeed so low is yet to be resolved, but I took it to Sudesh.

He disconnected the tubings and separately gassed up with nitrogen the evaporator, the compressor and the condensor - no leaks. he then put everything back together and checked, including soapy water on the joints, and there was a leak from the low pressure end of the compressor. Why the earlier guys couldn't spot it, is yet another question to resolve (soapy water doesn't seem rocket science)

anyway, the double-lip seals that PSA use are not (readily) available (Sudesh said even carmart doesn't stock it) so he tested it with 2 regular rings of same diameter, and it seemed to be holding pressure. So we decided to charge it with gas, including the UV dye (in case there was still a leak elsewhere), and when everything was hooked up, the compressor didn't switch on. He fiddled with some wire (I thought it was the power to the compressor) but turned out it was the pressure sensor on the condensor pipes and the AC kicked in; gassed the system up and cool air was blowing from both sides - so would suggest that the flap motors are not faulty. (also subsequently another guy on UK forum had similar issue - warm on driver side - and a regas helped him as well).

however, driving home, I discovered the AC was not working so drove back - gas pressure still OK (no fantastic leak for 700g of gas to disappear in 10 minutes); but AC doesn't stay on - can hear the clutch kicking in, but almost immediately disconnects. as there cannot be abnormal pressure (390 PSI is the safety cutoff, guage shows ~250) and it's also not the engine temp (normal) it would appear to be a faulty reading from the sensor... As I drove home, I "tested" the AC every now and then, and once it did engage long enough to give some cold air from the vents. I'm hoping it was just because it was disconnected when pressure testing the condensor and that some contact cleaner will help it behave again. Otherwise I have to get it hooked on a lexia to figure where the cutoff signal is coming from...

thanks all, will keep you posted as the saga develops :S

[The Don]

So you didn't actually use the recently acquired compressor ? I think the two points where the signal can come from is the pressure cut off (it could be faulty and kicking in way too early) or the temperature sensor on the evaporator to prevent ice on the evaporator (again this could be faulty). Other than that I can't really think what it could be rather than an issue with the compressor (the signal is there but clutch disengages) or an electronic issue (faulty control unit).

[Sifaan]

So you didn't actually use the recently acquired compressor ?

well, the folks at wimal motors had installed the new compressor anyway.

I think the two points where the signal can come from is the pressure cut off (it could be faulty and kicking in way too early) or the temperature sensor on the evaporator to prevent ice on the evaporator (again this could be faulty). Other than that I can't really think what it could be rather than an issue with the compressor (the signal is there but clutch disengages) or an electronic issue (faulty control unit).

well, I'm hopeful it's a contact issue on the pressure sensor since that was disconnected in the checking process; but there is also an interesting observation that the AC worked this morning on the (short) drive to work - must run it for a while and see if the gremlin has worked itself out.

btw sudesh was saying that as compressors, etc. age the amount of gas needed can increase beyond the recommendation; weighing the cylinder before/after the operation showed 770g of gas used, which is ~10% more than the 650-700g recommendation. of course some of that 770 was lost in the gauge. I'm not sure if I buy the "used compressor" argument;

was wondering if tropical countries need more gas as we're trying to create a larger temperature difference between inside/outside than in temperate climates, however I think that's what the compressor duty cycle is for.

[The Don]

well, the folks at wimal motors had installed the new compressor anyway.

well, I'm hopeful it's a contact issue on the pressure sensor since that was disconnected in the checking process; but there is also an interesting observation that the AC worked this morning on the (short) drive to work - must run it for a while and see if the gremlin has worked itself out.

btw sudesh was saying that as compressors, etc. age the amount of gas needed can increase beyond the recommendation; weighing the cylinder before/after the operation showed 770g of gas used, which is ~10% more than the 650-700g recommendation. of course some of that 770 was lost in the gauge. I'm not sure if I buy the "used compressor" argument;

was wondering if tropical countries need more gas as we're trying to create a larger temperature difference between inside/outside than in temperate climates, however I think that's what the compressor duty cycle is for.

Well if the compression is not as efficient as it used to be, then having more gas might actually make the situation worse as that would make the gas more difficult to compress even more !. I would thing the missing 70g can probably be explained via weighing inaccuracies, gas lost in transport etc ....

Actually the problem you describe has been experienced by me, when my car was wrongly fitted with a Townace compressor and the car was gassed up to the maximum. The pressure cut off kicked in straight away and disengage the clutch. That is unlikely in your situation.

I wonder if there is actually too much gas in the system triggering the pressure cut off. This would actually be worse during the day when the sun is out as warm gas is a lot more difficult to compress than cold gas !

[Sifaan]

Well if the compression is not as efficient as it used to be, then having more gas might actually make the situation worse as that would make the gas more difficult to compress even more !. I would thing the missing 70g can probably be explained via weighing inaccuracies, gas lost in transport etc ....

missing 70g? I have excess 70g (less whatever was lost in the gauge), scale measured 13.785 and 13.015 so the weighing errors are likely insignificant. not sure what you meant by transport?

Actually the problem you describe has been experienced by me, when my car was wrongly fitted with a Townace compressor and the car was gassed up to the maximum. The pressure cut off kicked in straight away and disengage the clutch. That is unlikely in your situation.

I wonder if there is actually too much gas in the system triggering the pressure cut off. This would actually be worse during the day when the sun is out as warm gas is a lot more difficult to compress than cold gas !

I took it back to Sudesh that day and he hooked up the gauge, and the pressure certainly wasn't rising high (cutoff 390 PSI); actually it wasn't even reaching 250 cos the compressor kept cutting out.

unless it is thermal related (i.e. work when cold, not when warm) I think it's not a problem with contacts (although will try contact cleaner on it just in case) - ac switched on when I left work; then cutoff after a while; subsequently it was possible to get AC back working (for a while) by either switching ac off for a while before turning on again, or turning off the engine (a 1 minute timer on the safety cutout for pressure is reset by engine off).

[The Don]

missing 70g? I have excess 70g (less whatever was lost in the gauge), scale measured 13.785 and 13.015 so the weighing errors are likely insignificant. not sure what you meant by transport?

I took it back to Sudesh that day and he hooked up the gauge, and the pressure certainly wasn't rising high (cutoff 390 PSI); actually it wasn't even reaching 250 cos the compressor kept cutting out.

unless it is thermal related (i.e. work when cold, not when warm) I think it's not a problem with contacts (although will try contact cleaner on it just in case) - ac switched on when I left work; then cutoff after a while; subsequently it was possible to get AC back working (for a while) by either switching ac off for a while before turning on again, or turning off the engine (a 1 minute timer on the safety cutout for pressure is reset by engine off).

What happens if you disconnect the safety cut off ?