A/C electrical problem

JLPARK1

MEMBER
1995 ISUZU TROOPER
3.2L
V6
4WD
240,000 MILES

After having a auto shop remove and replace AC compressor dryer and expansion valve power to the clutch relay did not work. Technician diagnosis says Addie relay PCM is not supplying ground to the compressor so they used a jumper wire on the compressor relay. Before the remove and replace everything work, but not very well. The clutch was going out in the compressor was going bad also. That is why I changed it out. I am going to supply the schematic that he is giving me see if you can make heads or tails out of this.

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Thursday, July 5th, 2018 AT 7:09 AM

5 Replies

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Hi and thanks for using 2CarPros. Com.

I looked at the schematic and yes, what he says makes sense. However, since the compressor engaged prior to repairs, I question that the PCM is bad has gone bad. There is an AC pressure switch mounted on the left front (near radiator) to the accumulator. I would ask if that has been checked. Also, do you think they would provide the low and high side pressure readings when the system is engaged? If pressure is too low, the pressure switch will not allow the PCM to provide ground. If you provide power and ground, it does not have a choice but to engage.

Now, I have looked through my schematics and it shows the compressor ground is through its mount. It does not go to the PCM/ ECM. I have attached my schematic for your review. Basically, what I see is ground is not provided by the PCM/ECM but rather, it comes from the compressor mount which is attached and grounded to the engine.

I hope this helps. Let me know if you have other questions.

Take care,
Joe

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Thursday, July 5th, 2018 AT 6:04 PM

JLPARK1

MEMBER
6 POSTS

Thank you for the help on my problem. I have two questions; first off do you have to evacuate the system to check the pressure switch? Exactly how do you check the pressure switch on or off the vehicle? Thanks again you been a big help. By the way I am hoping that they checked the switch, but it does not show up on the bill. All they were going to do was the remove and replace the compressor the dryer and the expansion valve. I am sure hoping they would check it to make sure, but I cannot guarantee it so I am going to have to call them. Thanks again.

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Thursday, July 5th, 2018 AT 8:09 PM

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Hi again. No, the pressure switch is usually checked when the system is charged. With manifold gauges attached to the system, the low side and high side pressures can be checked. The purpose of the component is to protect the system. If pressure is too low or too high, the circuit shuts down the system to prevent damage.

So, no the system shouldn't be evacuated; it should be fully charged. To determine if the switch is working, usually the pressure in the system will indicate an issue. In my first post, I mentioned it would be helpful if the mechanic would provide the low side and high side pressures. By any chance, is that information on the receipt?

Let me know. And remember, there is no such thing as a bad question. I am here to help.

Take care and have a good weekend if I do not hear from you.

Joe

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Friday, July 6th, 2018 AT 7:28 PM

JLPARK1

MEMBER
6 POSTS

Thanks again Joe for all your knowledge. As for the hi and low numbers on the receipt, no there was not any. But As I was following the schematic wire colors I came across the pressure switch connector which on my year trooper is attached to the top of the dryer. One of the female leads that plug into the switch was off the switch, funny thing is that they were stand-alone wires all my other connectors that I can see are plug in type. I replace the jumper wire with a brand new compressor relay and so far ice cold air! I am still going to take it to the place that fixed my Trooper in the firsthand. I will keep you posted.

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Friday, July 6th, 2018 AT 9:58 PM

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

You are very welcome. I actually enjoy having a chance to help. I am glad you found the issue. I had a feeling it was something simple like that. And, I am glad you got it working.

Take care, have a good weekend, and good job.

Joe

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Saturday, July 7th, 2018 AT 8:11 PM