A/C clutch not engaging

Hi,

On the relay, there is a primary and secondary side. On the primary side, pins 85 and 86 will get power at all times but the circuit isn't complete until the PCM provides a ground path. When that happens, the coil in the relay is energized closing the secondary switch and sending power to the compressor.

We know if you jump pins 30 and 87 the compressor engages, so that's good. However, I need you to check if pin 86 has power when the key is on. If it does, you need to check if there is a ground path provided by the PCM when the AC is requested.

I attached the schematic below for your reference.

Let me know what you find or if you have other questions.

Take care and Happy 4th of July.

Joe

See pics below.

Hi Lou,

The schematics are for the diesel model. The only thing that I can think of that could be different would be if this is a 2500 or a 3500. Even then, they should be the same.

Also, let me know if you have automatic climate control or manual. Same with this; it should be the same.

For me to confirm things, let me know the 8th digit in the VIN, there are two different listings for the diesel. If you look at the pic below, it shows the connector and pin number are different based on the engine code (VIN).

Let me know.

Joe

Hi,

The VIN changes a couple of things. To answer your question about the switch, no, the PCM provides the ground. The HVAC control module sends a class 2 serial data message to the powertrain control module (PCM) for A/C compressor engagement. The PCM will provide a ground for the A/C compressor relay enabling it to close its internal contacts to send battery voltage to the A/C compressor clutch.

On your vehicle, the ground path at the PCM is provided by connector 3, pin 41. The serial data wire is white from the controller and changes to dark green at the PCM. This is in connector 1, pin 15.

Remember, the ground is provided by the PCM when it receives a signal via the serial data link that A/C is requested.

If you look below, I attached the entire HVAC wiring schematic. It was two pages, so the first 4 pics below pertain to it.

The last 2 pics are specific to the AC compressor circuit.

Let me know if this helps or if you have other questions.

Take care,

Joe

See pics below Note: There is a splice in the serial data line which changes the wire from white to dark green. If the splice has failed, that will prevent the PCM from providing a ground path to the compressor relay. I added the last pic late. It explains where the splice is located.

The codes are all related to an issue within the serial data communication lines.

The U1016 is the powertrain control module. It is identified as 016 in the code. See pic 1 below. However, you indicated continuity to ground via the PCM.

Now, if you have a ground path provided by the PCM, you have power on both sides of the relay, and the power supply between the relay and compressor is good, the compressor should run. Are you certain the relay isn't an issue?

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Let me know.

Take care,

Joe

See pic.

Hi,

Yes, but there could be an issue with the PCM. Have you checked connections to make sure there is nothing causing it such as corrosion or a damaged pin/wire?

Joe