AC Relay Buzzing on Tow Vehicle

[KeithO]

In January, I had a mysterious persistent battery drain on my 2004 Suburban. I went through the exercise of putting my multimeter between the positive terminal and positive battery cable and saw that something was pulling about 5-6 amps continuously. I went through the exercise of pulling fuses one at a time until the amperage dropped to zero. This happened when I pulled the AC fuse.

As it turned out, the AC compressor relay failed closed and this was what was killing the battery. I replaced the relay and the problem went away, or so I thought.

Now that the weather is warm, the wife tried to use the AC and it didn't work. When I got home from work last evening I had a look and I found that the no-name autoparts store AC relay was clicking and when I fiddled it, it clicked even more. Today, while I was at work I had my wife go to the Chevy dealer to get a new Delco one. I just installed it and went around the block - viola! AC works. However, the new relay emits a buzzing sound. I turned off the car and removed it and it was smokin' hot.

My theory is that something else is wrong with the AC system which caused the original AC compressor relay to fail closed, engaging the compressor clutch and draining the battery. The no-name one just failed open, which is why I had no AC but wasn't draining the battery. I didn't beat the new one enough to make it fail but clearly something is wrong.

Anyone have any idea what I should be checking?

[roundel]

Sounds like too much current being drawn through the relay, arc welding it shut.  I'm guessing something that is shorted to ground (motor with the insulation melted on a few coils?)...

[Hunter]

Compressor clutch is most likely bad

[KeithO]

I got to the bottom of this.  A family of mice set up a home under the underhood fuse block.  I guess they couldn't resist chewing on some wires while they were in there.