I saw some earlier posts and followed them. I too am an electrician and did my due diligence troubleshooting. I jumped it out and it will engage. Checked fuses, relays, power returning on 85 terminal, changed low pressure cut out switch, checked pressures. Still not engaging. What now? HELP
Last edited by JPitt (10/16/2017 12:49 AM)
Before we go any further, what are the pressures on the gauges? The compressor clutch will not engage if the low side pressure is below 28 psi and the high side pressure is above 39 and 425 psi.
Did you check the clutch coil with an ohm meter?
The following conditions must be met in order for the ECM to turn on the compressor clutch:
Battery voltage is between 9-18 volts
Engine coolant temperature (ECT) is less than 123°C (253°F)
Engine speed is greater than 600 RPM
Engine speed is less than 4,760 RPM
A/C high side pressure is between 2929-269 kPa (39-425 psi)
Throttle position is less than 100 percent
Evaporator temperature is greater than 2°C (34°F)
ECM does not detect excessive torque load
ECM does not detect insufficient idle quality
The ambient temperature is above 1°C (34°F)
Below is the trouble tree from Alldata automotive information website. I hope it helps.
Ignition OFF, disconnect the A/C relay.
Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 and ground.
If the test lamp illuminates, test the control circuit for a short to voltage.
Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground.
If the test lamp does not illuminate, test the ignition circuit for a short to ground or a open/high resistance. If the circuit tests normal and ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary.
Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground.
If the test lamp does not illuminate, test the B+ circuit for a short to ground or a open/high resistance. If the circuit tests normal and B+ circuit fuse is open, replace the A/C clutch relay.
Disconnect the harness connector at the A/C clutch coil.
Test for less than 10 ohms between the ground circuit terminal 2 and ground.
If greater than the specified range, test the ground circuit for an open/high resistance.
Connect the harness connector at the A/C clutch coil.
Connect a 10-amp fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87. Verify the A/C clutch is activated.
If the A/C clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the A/C clutch.
Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
Command the A/C relay output function ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. A scan tool is helpful if you can get one to use.
If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.
If the test lamp is always OFF, test the control circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM.
If all circuits test normal, test or replace the A/C clutch relay.
Get back to me with your results when you can. We can diagnosis the problem further if needed.
Some information is from the Alldata information website.
Low side pressure was 45-50, clutch coil 4 ohms, battery voltage 14, don't have gauges to check high side pressure. All fuses are good, relays good, new pressure switch installed. Can remove relay and jump it and clutch will engage and cold air blowing, put relay back in and clutch does not engage. Don't have a scan tool, only multi-meter. Measured 14 volts across coil for compressor, got 14 volts on 85 to ground. Could it be a bad wire connection at pressure switch? I didn't check voltage there. Or could it be on the inside controls? All lights on panel show correct function.
If you jump out the low pressure switch does the compressor come on?
When you command the clutch to turn on at the control panel; check the terminal 86 at the relay for ground. This is the ground from the ECM to turn on the compressor. As long as all sensors are working inputs to the ECM it should command the clutch to come on.
It is possible you have a bad A/C control or ECM.
I am sending you a wire schematic for the clutch circuit I hope it helps. There are two of them I not sure which system you have.
I read once that the A/C module was electrically locked up and all the mechanic did was disconnect the battery for about 30 seconds and everything worked properly after. I know this seems far fetched but it wouldn't hurt to try. You never know you may get lucky.
I'm sitting here giggling over your last statement. Disconnect the battery. I did that yesterday, thinking the same thing. Far fetched but worth a shot. It didn't work. Thanks for the schematics and input. When my son gets home I will get back to it. I'll let you know.