A/C pressure out of range issue

[LSCaddy]

Hi
I've got an issue where my A/C relay will not turn on. I'm running a pressure sensor, 12212156 OS and 12212156 OS - V.9.0.xdf from here. Both are attached.

My A/C is set up as a non cycling analog system, with a pressure sensor and low temp cycling switch in series with the request signal. My low pressure cut in pressures are set around 60-70psi, max pressure around 350psi.

When I try to command the A/C relay with a scan tool I get an A/C pressure out of range error. The scan tool wont show A/C pressure as I'm running a truck OS and VIN, but I can see over 100psi using the logger that comes with universalpatcher.

Does anyone have an idea what my issue could be?

[darkman5001]

Hi
I've got an issue where my A/C relay will not turn on. I'm running a pressure sensor, 12212156 OS and 12212156 OS - V.9.0.xdf from here. Both are attached.

My A/C is set up as a non cycling analog system, with a pressure sensor and low temp cycling switch in series with the request signal. My low pressure cut in pressures are set around 60-70psi, max pressure around 350psi.

When I try to command the A/C relay with a scan tool I get an A/C pressure out of range error. The scan tool wont show A/C pressure as I'm running a truck OS and VIN, but I can see over 100psi using the logger that comes with universalpatcher.

Does anyone have an idea what my issue could be?

Greetings LSCaddy. On all of the different cars and trucks I work on, and I mean ALOT, if the PCM sees a pressure that is excessive, it will deny the compressor on request. You said that your cut pressure is set between 60-70psi. If you are seeing 100psi using the Universal Patcher Logger, then I would say that is the problem right there. The PCM is seeing 100psi and is preventing the compressor to come on. I would suggest you hook a set of gauges up to both your high and low side and see what the gauges are actually reading. Also if you are able to view live data, then you want to look at if A/C is requested and then if a/c is either granted or denied. I use a Snap-On scanner most of the time so I would go into the PCM, then Data, then usually A/C data is located under the Accessory list of data pids.

Also if you want to absolutely confirm whether or not the PCM is preventing the compressor from coming on, try this.

1. Pull the A/C compressor relay. (Typically it is a simple 775 relay)
2. Use a jumper wire and jump pins 87 and 30 momentarily while the engine is running and see if the compressor comes on. If it does, then your compressor power circuit side is good.
3. Check pins 85 and 86. One should have ignition power and the other pin is your control circuit, which the PCM controls to ground the relay to power the compressor.
4. If PCM denies compressor operation, then it will NOT turn on the control circuit ground. If PCM is allowing the compressor to operate, then ohm out the control circuit from the control circuit pin of the relay all the way to the pin in the PCM connector to see if the wire is broke or has high resistance.

If you need any wiring diagrams for your vehicle then let me know.


Hopefully this helps. Good luck.