Somebody please give me some advice on this, i need help.

My A/C compressor clutch will not engage.

I have charged my A/C system to the right amount of refrigirant.

I have tested my A/C pressure switch at the reciever/dryer, it is working.

My A/C thermostat inside my car is working correctly because my ECM is getting the A/C signal to bump up my idle and turn my fans on.

I have checked all of my fuses concerning the A/C and they are not blown.

I have tested my relays for continuity on the switch side of the relay while running power through it. They tested good.

However, I checked the ECM at pin 17 i believe at connector A, which is the ACC( A/C compressor clutch) with the A/C off in the car, and it tested at 13.06 V which is normal. I also checked it with the A/C on in the car and the voltage went down to 12.96 V which is not normal. With the A/C on I should read 0.00 V at pin 17 because the computer grounds the circuit.

I also checked for power at the compressor clutch itself and there is no power going to it. .

I should also mention that the red/blue wire coming from the ACC relay that goes to the ECM, I grounded that wire coming out of the relay and the compressor clutch engaged, and i went to the ECM and grounded that same wire and the clutch engaged again.

So I know I don't have a open circuit between the ACC relay and the ECM, and i know that my compressor does work with power going to it.

Do I have a bad ECM? Is it not grounding out the circuit like it is suppose too, which in theory is not sending power to the compressor clutch? I have checked all there is to check or so i think..

If I have missed something or you have had the same problem then PLEASE let me know what you did or how you went about fixing this problem.

THANKS in advance.

 

It must be voluntarily not turning the compressor on. How did you test the ac switch ? What do your manifold readings look like throughout ?

 

i tested the pressure switch for continuity after i charged the correct amount of refrigirant in the system. And I don't mean to sound dumb or nothing, but what do you mean by manifold readings?

I have access to ALLDATA at the shop I work at so i printed off a schematic of the air conditioning system, and I know the engine coolant temperature sensors are in this schematic, but my temperature guage on my cluster is reading operating temperature when warmed up, so that must mean my ect sensors are working correctly.

 

I believe what holmes is asking is...did you use air conditioning gauges to charge it. was it vacuumed out first ? did you weigh the charge in from a scale...into a completely empty system? a system can be overcharged and be held off by the high pressure switch. I'm not an expert but it sounds like you have a relay, or a pressure switch holding it off.

 

well I used a A/C machine and evacuated the refrigirant from it, put a 30 min vacuum on the system, and then put the spec amount of refrigirant back in it.

What other relays control this circuit? I know the compressor clutch, condensor fan, and radiator fan relay are good. Are there any more that I'm missing?

 

I am, by no means, an ac expert. I really only know the basics. It sounds like the system itself appears to be running fine with the exception of the something is telling the compressor not to turn. Two possibilities, but not the only possibilities I suppose, is the ac pressure switch is signaling too much or too little pressure or the ac thermostat is signaling that the evaporator is too cold.

You need to take pressure readings on the low and high side with the ac off and with the ac turned on. You need readings also while the compressor is cycling on and off but since it's not, obviously you can't do that.

 

That is two possibilities that I have thought about, but also when i turn on the A/C button in the car, my fans come on and my idle bumps up a bit. That tells me that power is going through the pressure switches and thermostat and sending the A/C signal to my ECM.

I checked the voltage in the car at the ECM at the A/C signal pin, and with the A/C off I had 12.96 V. When I cut the A/C on, that pin dropped to 0.00 V. That is normal.

I don't think that the power would get sent to that pin of the ECM if the pressure switches or the thermostat was bad because it would cause a break in that circuit. If I'm wrong though please correct me.

I will check the pressures though with the A/C off and let you know what they are.

 

to answer your question...i'm not sure

let's see what your pressure readings look like

 

I think you're on the right path. Power is going from the switch inside the car, through the thermostat, pressure switch, and then to the ECM to tell the fans and compressor to come on. Have you tried switching the compressor and condenser fan relays? If your fan is coming on, but the compressor isn't, there's a possibility that the AC compressor relay is bad and isn't sending the voltage to engage the clutch.

I've got a similar issue with mine, pushing the button inside turns the radiator fan on and increases idle, but neither the compressor nor the condenser fan come on. I checked the car side of the relays and have ~12 volts. Checking the condenser plug with one relay I have ~10 volts and with the other, I don't have anything. I just ordered a couple replacements on Amazon which will be in Thursday, so we'll see if that fixes my problem.

 

BTW, replacing the relays fixed my issue.

 

thanks for updating

 

i appreciate the help but i have already tested my relays and they are both in working order, i believe the ecm is my problem in this case.

 

I would not be surprised at all. I have two ECUs and they both throw CELs for different things. One doesn't like my distributor and the other doesn't like my EVAP system.
I fix either problem by swapping ECUs.
Time for a third ECU.

 

oh wow that's crazy, do you know a good and cheap place to buy one?

 

Thanks my dad is having ahell of a time with this. He has replaced everything checked fuses jumped switches but when i mentioned ecu he found it and it wws blown. Hes switching it noe it will probanly work.