Coolant Temp Switch

sira · January 21, 2011

Dear All

This question is related with my previous question of AC condenser fan.

My EK3 had a modification for the AC unit with bigger condenser. The radiator fan also modified with grounding the coolant temperature switch with relay circuit. When the AC is on the coolant temperature switch short with ground and both fans start working. and if the AC is off, and the Thermostat on the radiator fan start working.no issue

My question is , is this modification send the signal to ECU unit as soon as I switch on the AC? witll the ECU thinks the coolant circulation across the engine?. as far as I’m aware when the coolant start circulation thro engine the idle speed also will increased.

any way AC is on then also idle Speed will be incresed.

If this signal not going in to ECU then no issue. I ‘m having 98-00 Service manual for civic which is USA model(I don’t have Asian model). And it says it goes to ECU see the attachment. Any body familiar with this ECU here?

your ideas are most welcome

96_-_00_Honda_Civic_Service_Manual.pdf

The Don · January 21, 2011

Sira, no expert in ECU's and this particular model, so I guess we'll have to use logic here.

1. I'm not sure why the radiator fan had to be activated in this way. I mean you could have always used the relay just to turn the radiator fan on, or just rely on the car to turn the fan on when needed depending on the temperature.

2. When the engine temperature reaches a pre set point the thermostatic valve opens letting coolant flow more freely through the engine. I do not think the engine idle speed goes up at that point (I don't really see a need for it since the coolant circulation is controlled by the thermostatic valve, not idle speed), but I could be wrong.

I'm not an expert man, just sharing some thoughts. I actually have a similar problem, My car is a JDM and the radiator and condenser were both quite small and the AC guys replaced the condenser with a bigger one, which in turn covered the radiator. Now if I leave the AC on idle during a hot day the engine starts to boil (hence why people always need to take care when messing with the original design of a car). I think I'll have to pump up the cash and invest on a new bigger radiator and probably a radiator fan with a higher CFM rating ! The AC is ice cold though

sira · January 21, 2011

Sira, no expert in ECU's and this particular model, so I guess we'll have to use logic here.

1. I'm not sure why the radiator fan had to be activated in this way. I mean you could have always used the relay just to turn the radiator fan on, or just rely on the car to turn the fan on when needed depending on the temperature.

2. When the engine temperature reaches a pre set point the thermostatic valve opens letting coolant flow more freely through the engine. I do not think the engine idle speed goes up at that point (I don't really see a need for it since the coolant circulation is controlled by the thermostatic valve, not idle speed), but I could be wrong.

I'm not an expert man, just sharing some thoughts. I actually have a similar problem, My car is a JDM and the radiator and condenser were both quite small and the AC guys replaced the condenser with a bigger one, which in turn covered the radiator. Now if I leave the AC on idle during a hot day the engine starts to boil (hence why people always need to take care when messing with the original design of a car). I think I'll have to pump up the cash and invest on a new bigger radiator and probably a radiator fan with a higher CFM rating ! The AC is ice cold though

thanks for your reply, i think the radiator fan of your car is not good.

i have checked few of my friends who using EK3 JDM and lots of them said they have modified the AC with biggher condenser and it dose not affect other engine systems. how ever i spoke to Honda agents and they aslo said they have modified with the biggher Condenser, but dont know the coolant switch wire go ECU or not ,before the EK3 i had nissan FB13 and that car idle speed will changed doring cooland circulation.

The Don · January 21, 2011

I see Sira, then you're probably right, the engine idle might go up when the radiator fan is activated.

I thin if the switch is activated by relay (which is what grounding does) then the ECU must be informed as well. But like you say in real life this is not an issue as idle speed is up anyway during AC operation.

Yes my fan is problematic, but what really caused the problem is before the radiator was open to air from the front so cold ambient air could come in and cool it. Now there is a condenser in front and the fan is actually pulling in warm air not air at ambient temperature as before. Either I need a smaller condenser, a bigger radiator, or a more powerful fan ! I think I prefer the bigger radiator, as long term it's the best option, plus there is a factory made bigger radiator for my car. Mine was small because it is a JDM.