I have a 04 lariat. I had a new A/C unit installed. The clutch will stay engaged when the truck is turned off and run the battery down. All the grounds have been checked. I have to pull the relay to disengage the power to it. So I bought a new relay and it will not engaged the AC. When I put the old one back in, the AC will kick in. The CHT sensor harness needs replacing, I don’t know if that has anything to do with it.
Any ideas will help!!

 

Sounds like the compressor clutch needs adjustment... believe there are shims

 

No, the gap will not cause a continued electrical drain.

No. When the ignition is turned OFF, power *should* be removed from the circuits that are needed to energize the clutch relay.

Sounds like the original relay is stuck in the closed position. The replacement relay is either defective or there is some other electrical fault in the relay's control circuit that is preventing it from working.

Have you been able to determine if the clutch cycles during operation or does it always remain activated?

It's going to take either actual electrical troubleshooting or a lucky guess to solve this issue. You'll need a multimeter along with a scan tool and some work to properly diagnose the issue. If you're interested, equipped, and able to follow directions, we can help. If you're not comfortable doing that, it would be best to find a shop with a tech who understands the system and can diagnose it.

 

You need to see if electrical signal is coming to the relay coil . Sounds like the relay is either welded shut or has been jumpered on the pins . The pcm controls the clutch relay . The hi and low refrigerant switches go to the pcm . The pcm will not run ac if it has high cly head temp ,trying to protect engine from further heating . It does other things to stop the overheating short term . The clutch power is on at all times if relay contacts closed . So yes it would run your battery down if relay stuck on . But coil power is only on in run or start and pcm supplies ground if it wants clutch on . So it sounds like the old relay contacts is defective or jumped on . You need a voltmeter or test light to find out . Perhaps your new relay is the wrong one or defective also but it sounds fishy ,like someone had jumped contacts on old relay

 

The clutch runs continuously. I even turned off the the AC in the cabin and it still runs. I can give it a shot to trace it down.

 

After I responded I went out with a test light and checked where the relay plugs in and found that there is a continuous hot on the female plug. With and without the ignition on.

 

1. Well, there's supposed to be ALWAYS HOT on one of the pins (pin 3). With the ignition OFF and the relay removed, the rest of the pins should be without power. Turning the ignition switch to RUN or START should apply battery power to pin 1 of the relay socket.

2. A resistance check from socket pin 5 to ground should be several ohms (through the coil).

3. A resistance check of relay socket pin 2 should be high, above several kOHMS. Do NOT check this with the ignition in RUN or START! I suspect you will find this line shorted to ground which means either a wiring short to ground or the driver inside the PCM has shorted. If grounded, disconnect PCM and repeat to isolate.

 

Thx for info. I’ll check the pins and go from there. I’m leaning towards that old relay being messed up.

 

The old relay being messed up does not explain the problem with the new relay.

 

As I stated previously - "The replacement relay is either defective or there is some other electrical fault in the relay's control circuit that is preventing it from working." I suppose I could have added "wrong one".