No A/C after 7427 conversion

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11-12-2021
Daveo91

1 Attachment(s)

No A/C after 7427 conversion

After I converted to '7427 this summer (from '7060) I noticed the A/C comp was not coming on when selected an A/C mode or defrost. But I had so many things to work out then that I put that problem out of my mind (after quickly checking to make sure that the connector had not fallen off the compressor clutch). Now I'm digging in to see what's going on.

1. A/C worked fine before conversion.
2. In conversion, wired dark green wire that was on B12 of 7060 to E12 of 7427.
3. Had dash apart recently and removed HVAC mode selector switch to test continuity. Appeared to test correctly for all A/C modes and DEF.
4. Fuse is good and HVAC mode switch getting 12v with ignition on.
5. I data logged today and while logging I selected multiple A/C modes and DEF. Exported log and checked: PCM not registering that A/C has been commanded.
6. Just checked and light green wire at pressure cycling switch is getting 12v when A/C mode is selected.

Based on all this the only thing I can see in the wiring diagram would be the pressure cycling switch is bad? Anything else I'm missing? Not sure how to test that switch. I checked continuity and current state is open. Guessing it's stuck in that position and not allowing signal to compressor clutch and PCM?

Attachment 17278
11-12-2021
NomakeWan

Quote:

Originally Posted by Daveo91

After I converted to '7427 this summer (from '7060) I noticed the A/C comp was not coming on when selected an A/C mode or defrost. But I had so many things to work out then that I put that problem out of my mind (after quickly checking to make sure that the connector had not fallen off the compressor clutch). Now I'm digging in to see what's going on.

1. A/C worked fine before conversion.
2. In conversion, wired dark green wire that was on B12 of 7060 to E12 of 7427.
3. Had dash apart recently and removed HVAC mode selector switch to test continuity. Appeared to test correctly for all A/C modes and DEF.
4. Fuse is good and HVAC mode switch getting 12v with ignition on.
5. I data logged today and while logging I selected multiple A/C modes and DEF. Exported log and checked: PCM not registering that A/C has been commanded.
6. Just checked and light green wire at pressure cycling switch is getting 12v when A/C mode is selected.

Based on all this the only thing I can see in the wiring diagram would be the pressure cycling switch is bad? Anything else I'm missing? Not sure how to test that switch. I checked continuity and current state is open. Guessing it's stuck in that position and not allowing signal to compressor clutch and PCM?

Attachment 17278

Correct; the pressure switch should remain closed unless system pressure is above or below its set point. If it is open right now, then first you need to confirm that the system pressure is actually within specification. One of those parts store A/C refill bottles with the pressure gauge on it will do that for you. If you confirm that pressure is actually within the correct range, then the switch is bad and must be replaced.
11-12-2021
brian617

Check for 12v on both sides of the low pressure switch on AC drier. Very common failure. And it maybe obvious, but also check that you have enough charge to close the switch.
11-15-2021
Daveo91

Quote:

Originally Posted by NomakeWan

Correct; the pressure switch should remain closed unless system pressure is above or below its set point. If it is open right now, then first you need to confirm that the system pressure is actually within specification. One of those parts store A/C refill bottles with the pressure gauge on it will do that for you. If you confirm that pressure is actually within the correct range, then the switch is bad and must be replaced.

Quote:

Originally Posted by brian617

Check for 12v on both sides of the low pressure switch on AC drier. Very common failure. And it maybe obvious, but also check that you have enough charge to close the switch.

Thanks to both of you. Unfortunately I have a leak, at or near the condenser. I bought one of the parts store bottles with the gauge. Zero pressure initially and put some in and quickly figured out there's a leak in the line that goes from compressor to condenser, but it's behind the radiator so I couldn't pinpoint it exactly. Putting pressure on that hose can change the leak rate so I'm assuming it's where the inlet tube is brazed to the condenser body. I tightened the connection between the line and the tube just to be sure that wasn't the problem. I will have to pull the radiator to figure it out exactly. And then I couldn't get enough pressure in the system to verify if the low-side switch is working. I had engine running with A/C selected - compressor never came on even though I could get pressure close to the green section on the gauge, but not quite.
11-16-2021
brian617

Here at work I've rigged up a fitting to use regulated shop air with my A/C gauges to pressurize the system to find gross leaks with soapy water. Small leaks are easiest to spot with A/C dye and black light. Most leaks are usually accompanied with A/C oil too, another helpful hint.