AC has me baffled…

T4Rscott

T4Rscott

New member
Hey all,

I’m an completely baffled by my AC system.

I have gone through the entire factory service manual section on the AC system, and I have done all the diag, and it still won’t engage the compressor clutch at idle.

I had the the system flushed and refilled, I have replaced the pressure switch, the thermistor, the TPS, the IAC. Everything up to and including the ECU has been probed and tested.

The shop I used to evac and refill thinks it could be a weak magnet, I’m not buying into that. Someone else hypothesized to could be a pressure issue in the compressor.

Can anyone give me some usable advice? The next thing will be to swap in another compressor, and I’m not willing to undertake that without knowing if it’s going to solve the problem.

Thanks,
Scott
 
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Is the pressure the same on both high side and low side? If it does the compressor is blown. Does the pressure switch test properly?

If you supply 12 volt directly to the magnetic clutch does it engage?

If it engages this way, you getting cold air.

I haven't heard of a weak magnet. Mostly they engage or they don't.

All fuses good?

Sent from my SM-A505U using Tapatalk
 
The shop I took it to said the pressures were good. The switch is new. The clutch does engage when powered from the battery.
 
Then the clutch is good.
Does your ac button light up?

Maybe that Removable button and the ac circuity. These have either a analog or digital circuity depending in the years. The early years have a relay in that circuit. The kicks on and off with the compressor.

Sent from my SM-A505U using Tapatalk
 
T4Rscott said:
The shop I took it to said the pressures were good. The switch is new. The clutch does engage when powered from the battery.
Click to expand...
Will the ac function with the ac clutch on? You get cold air cooling off?

Sent from my SM-A505U using Tapatalk
 
Yes the AC button is working. It gives copious amounts of cold air when the accelerator is depressed and the AC amplifier kicks in.

And yes the amplifier is new as well.

I have literally done every test and diag for all the items that are most common and some that are not.

I’m leaning toward replacing the compressor and clutch
 
It’s hard to diagnose the ac system without knowing what the low and high side pressures are at idle and at 1500 rpm’s. Is the ac compressor clutch engaged at idle or does it only engage at higher rpm’s?
 
T4Rscott said:
Yes the AC button is working. It gives copious amounts of cold air when the accelerator is depressed and the AC amplifier kicks in.

And yes the amplifier is new as well.

I have literally done every test and diag for all the items that are most common and some that are not.

I’m leaning toward replacing the compressor and clutch
Click to expand...

Wait, you need to accelerate the engine to get the A/C system to blow cold air? If that's the case, either your pressures are too low or you have a restriction somewhere in the system (likely the expansion valve). Chances are that the vehicle is not seeing the pressures it needs to see and is turning the compressor off to preserve itself.

I would want to see pressures after it sits a couple hours, at idle w/o compressor engaged, at idle w/ compressor cycling, and at 1500rpm w/ compressor engaged. That should give you an idea of what you're dealing with if everything else is electrically good and functional.
 
Crazy problem, but try this,
Key on, engine not running, turn AC system on. AC clutch should engage even though the engine is not running. You should here a click. If not try advancing the accelerator by hand under the hood and see if the clutch will engage then- should hear the clutch pull in. If that is the case then it could be related to the throttle position sensor. Usually the TPS will turn off the AC when the throttle is at the wide open position.
 
Last edited:
kevincva said:
Crazy problem, but try this,
Key on, engine not running, turn AC system on. AC clutch should engage even though the engine is not running. You should here a click. If not try advancing the accelerator by hand under the hood and see if the clutch will engage then- should hear the clutch pull in. If that is the case then it could be related to the throttle position sensor. Usually the TPS will turn off the AC when the throttle is at the wide open position.
Click to expand...

Nothing happened.
 
Man extremely odd that it only engages at high rpm only.

So what happens if you manually just keep in engaged via 12 volt bypass to the magnetic clutch. Will your evaporator produce cold air out your vents?

Or warm air.. As your expansion valve can plug from debris.

Will all that new it cant shouldn't be the ac circuit. With new pressure switches it shouldn't be those. your getting down to the ac button and your compressor clutch. As everything else has been changed... :/
 
brillo_76 said:
Man extremely odd that it only engages at high rpm only.

So what happens if you manually just keep in engaged via 12 volt bypass to the magnetic clutch. Will your evaporator produce cold air out your vents?

Or warm air.. As your expansion valve can plug from debris.

Will all that new it cant shouldn't be the ac circuit. With new pressure switches it shouldn't be those. your getting down to the ac button and your compressor clutch. As everything else has been changed... :/
Click to expand...

The AC button lights up and is not flashing. I have not tried the bypass while running, only to actuate the magnet, which works. Would assume it would give cold air.

I’m going to try to run a bypass from the input for the original clutch to a newer unit and see if that makes any difference. If it doesn’t, I’m going to look into replacing the expansion valve.

I have even gone to the extent of replacing the IAC and TPS to rule that out.
 
T4Rscott said:
The AC button lights up and is not flashing. I have not tried the bypass while running, only to actuate the magnet, which works. Would assume it would give cold air.

I’m going to try to run a bypass from the input for the original clutch to a newer unit and see if that makes any difference. If it doesn’t, I’m going to look into replacing the expansion valve.

I have even gone to the extent of replacing the IAC and TPS to rule that out.
Click to expand...
The expansion valve has nothing to do with your compressor clutch not engaging at idle
 
I agree with Bad Luck, the expansion valve has nothing to do with it.
You already proved the clutch is good by connecting it to a 12 volt source, so rule out the clutch, problem sounds electrical. Look at the source of voltage- what controls the system to make the compressor clutch engage. If power for the clutch comes from the relay, check the control side - ie- what makes the relay activate, and check the power side of the relay-ie voltage to the clutch.
Check the ground circuit for the clutch, you can also look for a high resistance in the circuit from the relay to the clutch and on the ground side with and ohm meter. You should be able to do this without running the engine. When checking for ohms make sure power is off or you may get bad readings
If the control side of the relay is not making the relay work, then it could be the low pressure switch, or wiring, could be the on/off switch in dash or wiring
The low pressure switch turns the AC system off if there is a low charge - typically below 20 psi.
Find a wiring diagram and trace the system out.
 
kevincva said:
I agree with Bad Luck, the expansion valve has nothing to do with it.
You already proved the clutch is good by connecting it to a 12 volt source, so rule out the clutch, problem sounds electrical. Look at the source of voltage- what controls the system to make the compressor clutch engage. If power for the clutch comes from the relay, check the control side - ie- what makes the relay activate, and check the power side of the relay-ie voltage to the clutch.
Check the ground circuit for the clutch, you can also look for a high resistance in the circuit from the relay to the clutch and on the ground side with and ohm meter. You should be able to do this without running the engine. When checking for ohms make sure power is off or you may get bad readings
If the control side of the relay is not making the relay work, then it could be the low pressure switch, or wiring, could be the on/off switch in dash or wiring
The low pressure switch turns the AC system off if there is a low charge - typically below 20 psi.
Find a wiring diagram and trace the system out.
Click to expand...

I’ll be digging into my FSMs this weekend.
 
Yes agree with the others that the expansion valve only has to with cooling in the Condenser.

Sent from my SM-A505U using Tapatalk
 
Do you have 12+ volts at the connection on the compressor at idle? Is it possible the air gap on the clutch is too wide? it should be about .025".
 
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