AC/Fuse Box Can of Worms

2003 4x4 MT 3.4L engine

A common issue, AC clutch not turning and have been following along in this thread. I was attempting to follow this video which is straightforward but his fuse box layout is different than mine, I can't switch the horn and AC relays to test. I went to O'Reilly's and replaced the 50A fuses, one of which fell apart on removal, and picked up a "multi-purpose relay" to swap out with the OEM just to test.

BIG MISTAKE. At least I think. Nothing changed, and as you know the relays are difficult to get out, as I was using a plastic body tool to attempt to pry it out from the bottom, I got a BZZT and puff of smoke from approximately the Tail relay area. At first I thought it was me wiggling around getting the relay out, but on further inspection it must have been heating up and chose that moment to fry.

Pulled the battery, dismantled the fuse box, the insulation had melted in multiple spots on the wire from the heater relay wire into the (fusible?) link/harness plug attached to the inside of the box. No other wires were affected, so it wasn't shorting out against another wire. It looks like the exact wire as this member's problem but different M/M/Y. It also blew one of the 50A fuses I just replaced. The wire is safely insulated in shrink wrap now, everything works except the original problem LOL

The questions:

My first guess is this "multi purpose relay" effed up the circuit. The O'Reilly system says it fits, do you think that's it? I'm getting an OEM to be sure before changing anything else. I can't locate any info on properly testing for compatibility.

The second possibility is the new relay is fine and it's the compressor clutch that is shorted out, so by putting in a new relay it allowed the circuit to short out and fried the wire. The heater motor and other components are fine, does that sound like a reasonable assessment? In this case I'm reluctant to put in a new relay until that's resolved.

Still haven't applied power to the magnetic clutch because fiddling around with getting the wires out of the fuse box took all afternoon. :-\ Before doing that, I'll now check if the positive lead on the clutch to see if it shorts back to ground.

For anyone wondering (couldn't find it here) the P/N for the Heater Relay is

90987-04002 (90987-04002-83)
656700-6780

The O'Reilly PN in question is "Import Direct Multi Purpose 5 terminal relay" 25-0134

 

Any marking on the New relay

my 2000 the heater relay pins 3and 5 are the coil pins 1 and 2 are the contacts when the contacts are open pin 4 goes to ground. The pins are labeled on your fuse block you posted. Do you have the AC diagram for your2003 if so you can double check

While the multi fit relay might work the pins might not match the relay socket in the truck.

You would need to know what pins on the relay are the contacts and which are the coil and match them to the truck relay socket with jumpers if they are not a match.

When you plugged in the new relay the ignition was in run the AC switch was on and the blower motor was on??

All the pressures were correct the switches were closed to allow the Magnetic clutch to be energized?

I wish Iwas close enough to help Been doing this type of work at times forever other times seems like a few months.

 

Yes and . . . .

So it's entirely possible the "new relay" was the problem. I should go into studying the relay circuits, haven't done that yet but have a new OEM ordered.

I have the downloadable FSM, it should be in there somewhere.

Nope! Everything was off but the battery was still connected. Fried the wire insulation, blew the 50 amp heater fuse, as soon as I got it all back together everything appears to function normally (except the AC of course.)

Yeah that's the thing, I'm wondering now if the power test on the clutch is okay, it could be something else entirely. First things first, I've been called away on another project, still haven't had the chance to do that. It could be low freon, some other component which I' currently clueless about. If the clutch is good, I'll likely take it to someone to see how much it will cost me. :-\

Yeah me too, probably have it figured out in minutes LOL! This is all very helpful though, thank you for your help and I'll report back as soon as I test the clutch.

 

Remember reach down from the top no crawling underneath .

I have no idea if manifold gauges and vacuum pumps can be borrowed like other tools makes AC work much easier.

If the system is low or empty.

If you take it to a shop on a vehicle this old more then likely to prevent comebacks they will want to change the main components which can get quite expensive. This appears all to common .