Turn Off A/c From A/c Button Or Blower

[Nirosha]

What is the difference between turn off A/C from A/C button and turn off from blower? If I turn off using the blower is the compressor still working? Because I heard that turn off and turn on the A/C frequently is not good for the compressor.

[harshansenadhir]

Think of it this way, when it automatically turns off and turns on you dont see any difference on the pulling power of the engine right? but once you turn it off and turn it on you feel like a huge load has been placed on the car isnt it, so such an sudden pressure on your car should affect it somehow.

That won't make any difference, automatically or manually, you shut off the electric coil in the a/c compressor which releases the clutch. It equals to a clutch engage / disengage cycles.

Also Most of modern cars equipped with a mechanism to automate this 'turbo boost' thing many have been discussed. If TPS detects a sudden depress of the throttle, ecu or a/c control module will immediately shuts off compressor temporary and re-engages in a while.

[NRX]

Think of it this way, when it automatically turns off and turns on you dont see any difference on the pulling power of the engine right? but once you turn it off and turn it on you feel like a huge load has been placed on the car isnt it, so such an sudden pressure on your car should affect it somehow.

Dang! Seriously I was always wondering about that. it doesn't feel any significant power difference when the compressor is automatically disengaged. Weirdo!

That won't make any difference, automatically or manually, you shut off the electric coil in the a/c compressor which releases the clutch. It equals to a clutch engage / disengage cycles.

Also Most of modern cars equipped with a mechanism to automate this 'turbo boost' thing many have been discussed. If TPS detects a sudden depress of the throttle, ecu or a/c control module will immediately shuts off compressor temporary and re-engages in a while.

Care to explain the above point mate ? THe power difference bit

[harshansenadhir]

Care to explain the above point mate ? THe power difference bit

What I said was there is no difference whether you switch off A/C button manually or thermostat cuts it off. In both instances what happens is current supply to the coil inside the compressor clutch unit gets disconnected and the coil gets de-magnetize. This makes the clutch to release. When the supply re-connects, the coil gets magnetized and engages the clutch.

[NRX]

Think of it this way, when it automatically turns off and turns on you dont see any difference on the pulling power of the engine right? but once you turn it off and turn it on you feel like a huge load has been placed on the car isnt it,

What I said was there is no difference whether you switch off A/C button manually or thermostat cuts it off. In both instances what happens is current supply to the coil inside the compressor clutch unit gets disconnected and the coil gets de-magnetize. This makes the clutch to release. When the supply re-connects, the coil gets magnetized and engages the clutch.

Harshan. What I meant was I have exactly felt what magnum ( quoted post) has mentioned, Do you guys know the reason for that ?

[harshansenadhir]

may be a placeboo effect. Another reason would be that you know very well at which point you switch off the A/C and may be flooring at the same time and assumes this contributes better towards releasing engine load.

[Magnum]

Dang! Seriously I was always wondering about that. it doesn't feel any significant power difference when the compressor is automatically disengaged. Weirdo!

Care to explain the above point mate ? THe power difference bit

Exactly, i dont think what happens in both situation is the same.

[Fixzit]

Has any one every thought about why car makers never makes cars in a way that the A/C is automatically turned off when you start the car? Obviously not because it's too expensive to do so or it's too complicated...simply because it's not necessary. They can easily put a few seconds of time delay from the start to turn the clutch of the compressor on after a start but it's not needed. Leave the A/C on guys.. I never turn mine off and never had a problem. Your starter motor s got plenty of extra power to turn your compressor as well..

If you are thinking that you can save fuel by turning your A/C on and off manually.. that is a silly thing to do too. Every time you turn it off by hand your cooler gets warmed up because the air inside of your car is still too hot(Otherwise the thermostat must have already cut off your A/C before you did) and put extra load on the compressor when you turn it back on thus using even more fuel than normal because then the compressor will take more power out of your engine to compensate the extra load. As some of the guys pointed out it's a good idea to let the thermostat do it's job and you concentrate on the road . I do like to point out that it's not actually the same if you turn the A/C on and off by hand (manually) and the thermostat cutting it off. Simply , if you turn the A/C off because you feel the temp inside the car is good enough for you, but the thermostat works according to the temp in the cooler. It's not usually the same and the load to the compressor is mainly decided by the expansion valve which works with the temp of the cooler. So you'll be better off letting the expansion valve and thermostat do their work by themselves. What you can control of course is the blower fan speed. Lower you run it the cooler the cooling coil is and the expansion valve closes to maximum taking load off the compressor and thermostat will cut the compressor off.. that's how things works ...

If you really wanna save some fuel money with the A/C... use the following tips..

1.If the inside is too hot while you get in the car, open all windows and let some cold air from outside to come into the car rather than asking your A/C to take all the heat out. You can get this heat out through the A/C but you'll be using extra fuel for that.. (Extra load = Extra Fuel)

2. If your car has a climate control function, put it on Auto and use it !! that's more efficient than using manual blower settings..I've seen lots of people not using this function, can't imagine why. Note that reducing temp setting does not give out more colder air from your air outlet, It will only increase the running duration to get up to the value which you have set. So leave the temp setting around 23-25... tips 3 & 4 below does not apply to you...so go to 5

3. If you have a just 3 or 4 blower settings, while the interior is hot use the fastest fan setting and gradually try to use it on the lowest setting as possible but this does not mean you use fan speed at 1 when there s burning sunlight outside with 34 degrees..because in that case you will be better off not using the AC at all rather than barely using it. Sole purpose of A/C is to keep you comfortable.

4. Adjust the vents towards you. If you are the only person in the car, and if you close your other vents and just leave the vents directed to you open, you can run the system under a lower fan speed.

5.Some cars comes with a return air filter or a cabin filter. It's a good idea to get it cleaned or if it's too blocked then replaced once every 6 months or so.

6.Keep your Condenser clean and do not let it clog. This will decrease the efficiency of not only the condenser but the whole system which puts extra load on the compressor. It's a good idea to check whether the condenser fan is working properly and also check the tension of the A/C compressor belt too. Slipping belt will decrease performance.

7.Do not turn the fresh air setting on because in SL, fresh air is hotter than recycled air most of the times which puts more load to the system and also fresh air will bring in dust with it which will eventually becomes mud inside the cooler and clog it, also it will rust the cooler to leak it.

Hope this will help to save you some fuel while using your A/C

Edited May 29, 2012 by Fixzit

[Nilantha]

oh!!!!! no have time to read.......................

[NRX]

oh!!!!! no have time to read.......................

He has mentioned some valid points, you should have read

BTW, I'm not entirely convinced by the first paragraph.

"Has any one every thought about why car makers never makes cars in a way that the A/C is automatically turned off when you start the car? Obviously not because it's too expensive to do so or it's too complicated...simply because it's not necessary. They can easily put a few seconds of time delay from the start to turn the clutch of the compressor on after a start but it's not needed. Leave the A/C on guys.. I never turn mine off and never had a problem. Your starter motor s got plenty of extra power to turn your compressor as well.."

[Fixzit]

A Little Correction...

Actually NRX is right !! I did some research and had a chat with one of my friend who's and auto electrician. He said, Just like when you start the car..all your accessories get turned off for some milliseconds (Lights, CD Player etc), your compressor clutch gets disengaged as well to minimize the load on the Battery. So regardless of the swich status (On/Off), It's the same thing..

[harshansenadhir]

A Little Correction...

Actually NRX is right !! I did some research and had a chat with one of my friend who's and auto electrician. He said, Just like when you start the car..all your accessories get turned off for some milliseconds (Lights, CD Player etc), your compressor clutch gets disengaged as well to minimize the load on the Battery. So regardless of the swich status (On/Off), It's the same thing..

Correct, this was the old school method. When the ignition key turned to the Start position, supply to all other accessories will be cut-off by the ignition switch itself. However, most of modern cars are now equipped with BSi s to handle such activities. In simple terms, they are capable of handling logics by considering multiple parameters (inputs)

A/C compressor switch on/off (engaging/dis-engaging compressor clutch) is one thing controlled by the BSi by considering certain logics.

Following is a list of such actions and the first one replaces the activity carried out by ignition switch.

1. After engine starts engages the clutch after about 10 seconds

2. If the compressor needs to be engaged, sends a signal to ECU to increase RPM and once engine revs up a little, engages the compressor clutch (avoids temporary vibration if compressor engages before RPM goes up )

3. If the TPS reads a sudden depress of the throttle, dis-engages the A/C clutch and re-engages after a while

4. if there's a critical system failure/ risk (limp-home mode, refregirant over pressured/heated, etc) dis-engages the compressor clutch.

Having said that, as VVTi also mentioned once, switching off the A/C prior to switch off the engine always helps the longevity of the entire system.

A/C system always runs with high pressure (280 psi and above) during the day time of a tropical country, specially these days. If you shut down the entire system at once, heated, pressurized refrigerant will be trapped on the high pressure side. If you first shut down the compressor (A/C switch) and then switch off the engine, it gives some time to cool down the trapped heated refrigerant as auxiliary fans still be running, or you give sometime to the system to run auxiliary fans and further reduce the temperature of refrigerant.

Some vehicles do equipped with auxiliary fans which will continue to run if required, even after taking the key-off but mostly it’s not the case. So best is to switch off A/C when you’re approaching the destination/parking-lot etc.

[Nirosha]

Wow. Thanks guys. Never knew such technical stuff.

Also thank you all for making this thread so informative. Peace without trolls.

[Fixzit]

Pressurized refrigerant will be trapped on the high pressure side. If you first shut down the compressor (A/C switch) and then switch off the engine, it gives some time to cool down the trapped heated refrigerant as auxiliary fans still be running, or you give sometime to the system to run auxiliary fans and further reduce the temperature of refrigerant...

I'm not so sure about this.. regardless of when you turn off the A/C compressor or the complete system, the pressure inside the system will always come the standing pressure of the system and this will be the same through out the system because high side starts from the outlet of the compressor till the very end of the expansion valve. When you turn off your system your cooler will get warmer thus opening the expansion valve more than before which balance the system. When you are not using the system, expansion valve is fully opened. You can even hear the refrigerant flow through the TX valve as soon as you turn the system off,,,but then turning your A/C off few mins before your final destination is a good idea...to remove some of the moisture trapped inside your cooler.. that will increase the longevity of the cooler considerably specially in a country like SL where there s lot of humidity in Air. No need to worry about the switch when you are starting up.. that's what I reckon !!!