AC Compressor only works when jumped.

2004 GTP. This ac is kicking my a$$. I have recently replaced the condenser, drier, compressor......

My issue is that my compressor only works when jumped. I checked the relay and 10 amp fuse located in the engine bay fuse box and both seem fine. I replaced the pressure switch and put a new pressure switch connector on it. I got it to take a full charge by jumping the compressor. It blows very cold when jumped. The outside temperature on the dash is reading correctly. Any suggestions???? I have limited knowledge on electrical diagnostics so any help would be appreciated.

With a/c commanded on- gently pull the a/c relay in and out- does it click each pull? If so, problem is between relay socket and compressor, or bad relay (swap it with horn relay).

If not, then problem is that computer is not allowing compressor to come on from a bad input or sensor. The pressure sensor you replaced should have been the 3 wire pressure transducer- were all three wires good? one is ground, one is 5 volt, one is reference voltage corresponding to refrigerant pressure- use your volt meter with sensor plugged in to monitor.

A Tech II scan tool would really help- other things like a bad engine temp sensor reading really hot will not allow compressor to engage- does your car have other issues?

No other issues. I replaced the relay with the horn relay and it did not work. Is there a way to test the sensors? On the oe connector it had a red wire with black stripe, a white wire and a black wire. The new one had a blue wire, grey wire and a black wire. I connected black/ black, red/ blue and white/grey. Thanks for the help.

The new sensor should have just plugged into your oem connector- why are you splicing? You may have gotten the wrong part. I would have tested sensor first- as described above.......

You may be wired wrong as well- you could fry the PCM (or at least make it unhappy) doing this wrong.

Where did you tap into compressor circuit to "jump" it?

I replaced the switch and connector. I replaced the switch first and then the connector. They sell a pigtail connector. I removed the relay and used a wire in between the top two pins.

Ok, I assume you have enough refrigerant in the system.....

The pressure sensor has 3 wires.....black is low reference....grey is 5.0 volts.....and red w/black stripe is you signal voltage.......since the new connector had different colored wires, did you reference the colors with the actual positions of the connectors of the old harness connector...black is #1, grey is #2, and the r/b was #3 terminal...

What you can do is check the red/black line.......for the AC to start, there should be around 1.5 volts on the signal line....if too high, 5.0 volts or too low, under 1.0 volts, the PCM will not ground the relay....have also seen bad connections at the UBEC(what the relay plugs into).........

Since the colors differ on the connector- then you ave to be sure the positions of the wires were maintained and wired in accordingly- hopefully you did that okay--- what made you decide to replace the pressure transducer?

Good that you jumped at the relay- much easier that way- no pin probing and the ground is always proved good as well.

Time for a TechII to tell you what input is unhappy...

I did have the connector wired wrong and rewired it :o .Unfortunately it still does not work. I will check the pressures again to see what they are. I could have used the air last night sitting in traffic for two hours at the Paisley concert :)

Ok I have some pressure readings.
when the compressor is not running the Low side reads 110psi and rising the high side reads 150 psi.

With the compressor jumped at the relay and running the low side reads 45psi and the high side reads 250psi.

It is about 90 degrees outside.

Do any of these readings mean anything to you guys? Unfortunately i do not have a tech 2 scanner just a plain old obd2 and my aeroforce gauge. I will have to take it to RadAir if i need to get it scanned. Thanks

You might try unhooking battery for 10 minutes - If there is an a/c code set- it may reset. Worth a try.

Ok I have some pressure readings.
when the compressor is not running the Low side reads 110psi and rising the high side reads 150 psi.

With the compressor jumped at the relay and running the low side reads 45psi and the high side reads 250psi.

It is about 90 degrees outside.

Do any of these readings mean anything to you guys? Unfortunately i do not have a tech 2 scanner just a plain old obd2 and my aeroforce gauge. I will have to take it to RadAir if i need to get it scanned. Thanks
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Would a code not allow it to run? Going by that chart it looks like the pressures are almost dead on, maybe low side could be higher but I think the compressor should be running where its at. I put about 37 ounces of freon so it should be ok. The pressure switch shouldnt be the issue because the pressures are ok.
Do the pressures matter when the compressor is off???
Maybe I should replace or check the other temperature sensor in the air duct??

Is your temp sensor reading properly? When they freak out and say it is 40 when it is really 90 the compressor won't run because it thinks it knows what you want. That's one of the reasons I hate digital climate. Like one time I was coming home one evening and it was a really cool 55* so I wanted a little heat. I set the heat to 75 and the car still blew cool air because it thought I didn't really want heat.

Yeah the temp on the DIC is accurate. Today it read 95 and it sure as heck felt like it. I think there is another sensor for the interior or evaporator temp somewhere. I may have to break down and get it diagnosed one of these days.

There is no other sensor- the system has a variable stroke compressor that adjust the refrigerant flow- so no evap sensor needed. A code could have been set when you had it wired wrong- or unplugged- and can only be reset by a scan tool or perhaps a battery unhook- worth a try in my opinion. Sure the pressures are fine on your gages- but what does the computer see? that is what the high side transducer is producing.

A Tech II scan tool will tell you what input is amiss- and whether or not it is commanding the relay and/or relay driver on or off.

If you are friends with a dealership- ask them to let you borrow one for a minute- sure would get you to your answer a lot faster than guessing.

You replaced the sensor and the harness at the sensor......but what if there is a wiring problem closer to the PCM or at the PCM?

You don't need a scan tool to check the signal voltage....have you checked it? If ok, then you need the scan tool to see if the PCM is reading the same thing....if there is a signal problem, causing the PCM not to ground the relay, a code should be set.....Could be P, B, or U......as the guys said, the Tech II scan tool will tell you if a code is set, if there is an AC request set, and if the PCM is commanding the AC relay on.....

I will unhook the battery to try and clear any codes. I have not checked the signal voltage. I do not know how or where to check, or what the voltages should be.
Does the scanner have to be a tech2 or will any scanner work? I appreciate the help guys!!! I do not know much about electrical or ac. I can do everything else though. Thanks again!!!

Once again- transducer input voltage is 5 volt, return signal voltage should vary according to pressure- but static pressure of 80 psi should yield a voltage near 1.0 volt- the other wire is ground- back probe the connector with it plugged into transducer to test. If you run the a/c return signal voltage should rise to 2-3 volts if working correctly.

Usually only a Tech II works for a/c codes- can't guarantee any others.