I am trying to recharge the ac in the car but the compressor won't turn on. I jumped the 2 terminals on the low pressure switch in the front. There is 12 volts at the plug. There is no voltage at the compressor plug for the clutch. The harness is made by Phonedawgs who doesn't answer his phone. Can someone give me some ideas as what to check. What are the typical wire colors for the relay?
I was doing some testing and found I'm not getting the negative from ac relay control. If I add a negative to the dark blue wire on the relay it will run. Now to trace the wire to the PCM. (Which that's where I think it goes) anybody confirm that?
There is two wires for AC on the PCM the wire from C203 pin D goes to one I believe PCM C2 21 it is a dark green with white stripe and PCM C2 39 again same colour is what supplied power to the compressor relay when the PCM is happy. To bypass the PCM control remove these two wires and short them together. This also eliminates the high pressure sensor though but is a good starting point. Double check the pin numbers though as I am going from memory. When AC is selected =12 volts goes to the low pressure sensor up front if good there it goes to C203 pin D then to the AC system
DARN Cars now open with Over 30 years wiring experience between cars and trade as an avionics technician in both Canadian Air Force and civilian aviation. Over 25 years experience building and modifying cars. Over 10 years of full Fiero engine swaps and harnesses building and still going.
It would tell if the PCM is commanding the compressor on or not by bypassing the circuit that the PCM controls. If it comes on then you know that the PCM is seeing a request signal but isn't doing anything with it. He is giving you your first steps to diagnose it. The A/C request signal comes from the climate control switch(Off, MAX, A/C, Vent, Heat, Defrost) will be on at MAX, A/C, and Defrost. If the PCM sees a request, good signal from the high and low pressure switches and your foot is not too far into the throttle and is not overheating, it sends a signal to the compressor clutch relay to turn on. When it gets a signal from the low pressure switch, around 20lbs, it turns it back off, around 50 back on. Cycling as normal. If the engine is overheating, by coolant sensor signal, or high side pressure is too high, or you just stomped the pedal, it also will turn it off. By bypassing the PCM compressor relay control, you can determine, if it is a relay, compressor clutch or related wiring problem before determining if you have a signal problem. If it does turn on, then you start looking why the PCM did not command it on. Example: ambient temp around 80. Low switch should be on. High switch should be off and if shows A/C request. PCM should command compressor on. At that temp if the hi switch is closed check for bad switch or grounded wire. At that temp if it shows low switch open look for broken wire or bad switch. Again an Example, I would have to look at a schematic to determine normally open or closed for the switches. You can also connect a scanner and see if you have A/C request, low and high pressure signals. Or something else the PCM don't like.
If the A/C compressor was working last year and it isn't working now, two immediate possibilities come to mind...
1) The outside ambient temperature read by the IAT sensor is too low for the PCM to permit A/C clutch operation. There is a minimum outdoor temperature threshold that has to be met in order for the PCM to allow for and command the A/C clutch on.
2) The pressure reading from the 3-wire A/C hi-side pressure sensor connected to the OBD2 3800 PCM isn't high enough to permit A/C clutch engagement. Possible causes for this could be too cold of outdoor temps or too low of A/C system refrigerant charge.
Of course you could have other issues, but these are the two that I could think of that could occur if the system was previously working (last year).
The scanner I am using doesn't show any a.c. info. I am lost...I get a negative output on #39 on the pcm. I get a negative at the relay on the dk/blu wire and a positive on the lt/blu wire but the relay won't pull in unless I add a negative directly the the dk/blu wire on the relay.
The OBD2 PCM (which I assume you are using) doesn't even look at the low pressure cycling switch. Instead, it looks at the voltage reading coming from the 3-wire hi-side pressure sensor - which it uses to determine actual system pressure. You should not try to "jump" the 3-wire pressure sensor.
30psi of refrigerant pressure in the system may be insufficient to permit A/C clutch activation. You need a proper A/C system refrigerant charge for the system to work properly. But I wouldn't just charge your A/C system now because obviously there was a leak and that needs to be repaired first.
Any time there is an A/C system leak, the oil in the system is usually the first to leak out. And charging up the system without making sure it has the proper oil level could lead to component failure because of an incorrect amount of A/C oil in the system.
The good news is usually when there is an A/C system leak, there will be evidence of such because there should be some A/C oil residue in the area where the leak occurred. The common places for Fiero A/C systems to leak are:
-Around the shaft seal to the compressor -Compressor half body seals -Any connection where there is an o-ring seal (lines) -Condenser core (usually caused by a road debris strike) -Corroded body lines running along side the fuel tank -Connection where the rubber flex lines are mated to the aluminum hard lines