Why does the A/C compressor run continuously?

Neil,

Low Freon won't cause this. My first guess would be the compressor relay is stuck and needs to be replaced.

I attached the wiring schematic below. It was one page, but I cut it in half, so you read it. I did overlap the two so you can follow from one to the other.

Here is what I need you to do: Pull the A/C relay in the under-hood fuse box. See if the compressor turns off. If it does, I would normally tell you to switch it with a different relay having the same part number. However, if I am correct and the relay failed internally, it will send power to whatever component you switch it with. So, let's just test the relay.

Here is a link that explains how it's done:

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

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

Take care,

Joe

See pics below. Pic 3 shows the relay.

Hi Joe.

Hi Joe,

I swapped the relay with the horn relay - no change. I tested the compressor relay. It tested 89ohms across the coil 85/86 and open from 87/30 - okay.
The female pins inside fuse box with relay removed read:
85/86 had 13Vdc in three scenarios: with A/C button pressed, when in defrost, and when air flow is on recirculate.
The clutch engages and never disengages in those positions. Is this supposed to cycle on and off like newer cars?
I need to get a manifold to see what the pressures are at.
The LP and HP cutouts are working as intended.
I found an air leak where the filter dryer / evaporator came through the engine compartment.
There is no insulation on the filter dryer as well.
Thanks for your time and thoughts.
Neil

Hi,

When you checked 85 and 86 was the relay installed? If the relay was out, only one side should have had power. You also mentioned that power was there when the A/C or one of the other modes was requested. So, I'm not sure if there was power at any other time.

As far as it running at all times, the system should turn on when the high side pressure sensor signals a drop in pressure, indicating the compressor needs to run. So, in theory, you could be low on Freon.

Also, if the compressor clutch overheated, it could simply be stuck. If you remove the accessory drive belt, see if the pulley spins freely. Obviously, everything needs to be turned off for this.

You indicated the high-side pressure sensor is good. If neither the high side pressure nor the A/C clutch are an issue, chances are you have a short to power at some point before the relay which is causing the relay to stay energized.

Let me know if you are able to check the things I suggested.

Take care,

Joe

Hi Joe,

Yes, the relay was out, and I was testing for power on the terminal block. Constant positive battery voltage present and switched negative that comes from the load side of the high-pressure switch in the three modes only.
I believe that’s normal.
I did not check the high side switch. I thought it was next to the radiator on the passenger side. Maybe that is a recirculation switch?
I will have to check freon pressures and then HP switch and clutch as you suggested and hope it's not in the ECM.
Thanks again for the guidance on operation!

Hi,

If you had power on both pin 85 and 86 with the relay removed, that doesn't make sense. One should have power and the other is open until a ground path is provided to actuate the relay's secondary switched side.

If you have power to both, that indicates the PCM isn't providing ground, but instead, it is sending power. That would indicate a short to power. I may ask you to disconnect the connector at the PCM and inspect the connection pins.

I may have misunderstood what you meant, so let me know.

Joe

I only had positive power at all times on 85. I had potential (13Vdc) in the three positions from the negative 86 to pick up the coil.
The switch side of relay also had constant positive and would engage when the relay energized as normal, sending positive 13V down to the clutch.
The clutch is not stuck, I can move it by hand. The A/C relay never drops out. As you’ve written before, it may be that the high-pressure switch never gets high enough to cycle, but enough freon to keep the LPS closed.
I will get some gauges and check pressures. What should they read?
Thanks

Hi,

At this point, I think that's a good idea. Let's see if it appears we have a low/weak charge.

Let me know what you find.

Take care,

Joe