[fripco]

I had the a/c compressor replaced on my '92 Corolla a few weeks ago. I drove it for about 2 weeks when the fuel gauge, temp gauge and the entire ac/blower system quit working. There's a 7.5a fuse labeled "gauges" that had blown. I replaced it and everything came back to life. It's burning out about every week now.

The a/c was down for about 6 months and this never occurred before.

My mechanic thought it might be the a/c condenser relay - it's on the same circuit. I found a used one and put it in, but with no success. I haven't taken it back yet to be looked at and was hoping to get some suggestions here. Is there anything connected with the compressor that could be causing this?

Thanks!

[TxGreaseMonkey]

My gut is to focus on the compressor clutch relay. I'm sure it's on the same 7.5A circuit.
The compressor clutch relay and condenser fan relay are usually mounted (side-by-side) next to the condenser fan. It would be simple for you to replace the compressor clutch relay yourself. Be sure to disconnect the negative battery cable first. There's also the possibility that the A/C Switch is bad. The worse-case situation would be for it to involve the ECM's A/C functional area, which undoubtedly is in the circuit.

If the problem persists, check out:

. Compressor clutch--there could be a short. Also, check related wiring and connectors.

. Condenser fan motor.

I would expect the compressor clutch and condenser fan motor to be tied into a 20A circuit, in the under-hood fuse box, not the 7.5A circuit in the under-dash fuse box. Therefore, I'm leaning toward the compressor clutch relay and A/C Switch being the source of the problem.

Without knowing more, this is the best I can do.

[fripco]

Thanks for the reply. The thing that puzzles me about this is that I ran the a/c for a year before the compressor went out with no problems. That makes me think that the problem is with the new compressor/clutch. How would I check to see if there's a short in it? Would that explain why it's so intermittent? Can a relay go bad if it's not used? That seems like a dumb question...

I know I can take it back to the mechanic who installed it and he'll make it right for me if it is the compressor, but it would sure be fun to find it myself!

[TxGreaseMonkey]

Relays can go bad from lack of use--they can start to hang up. It may try to actuate the solenoid and it can't do it effortlessly; then, it draws too much amperage and blows the fuse. Most things work better and last longer on cars when they are used regularly.

I hear what you are saying about the compressor clutch. However, I don't think Toyota would run this through a 7.5A fuse. You would need to hook a multimeter up to the field coil and check its resistance. Proper readings may be something like 3.2 ohms +/- 0.15 ohms at 68 degrees F. You would need to get the specifications for your coil.

[TxGreaseMonkey]

Kitch428 is our Toyota expert. You might want to PM him.

[kitch428]

The gauge fuse is directly tied in to the a/c. According to my wiring diag, the most direct tie in would be the heater/blower switch. (page 171 below in the pdf attach)
The switch gets hot and melts/shorts with age. I'd be looking there, or the integration relay.

If memory serves me correctly, I recall replacing more than a few Junction blocks with the integration relay built in due to 'hot spots'. Do a wiggle test and tap on the block to try and duplicate short.
As I recall, you found a donor car for picking parts off eh?

ac gauge.pdf

[fripco]

Thanks for the quick reply! "Integration relay" is a new one for me. Where would that be found?

Orlando has some great junk yards - lots of parts for the picking!

[kitch428]

J/B #1 is the fuse panel where you found the gauge fuse. That panel IS the relay. It's part of it. On the back side there's a long connector plugged into it. On the front side is all the fuses.
Many many things pass through it as part of integration. The gauge circuit is one of the most important. Of course, low amperage current is all that it needs.
You'll see it in page 19/20 below.

relayloc.pdf

[fripco]

Well, here's what I found tonight -

I knocked things around like you suggested - the fuse box, switch (all different settings), wiring, etc... and couldn't get a short to occur. One thing I did find, though, was the connecting wire from the compressor clutch to the wiring harness was not secure. It pulled loose when I was jiggling the wires. Could a loose connection there cause the problem that I'm having?

By the way, Kitch428, I saw your reply concerning the Camry door handles and the bad feedback. If I ever come across like that, take a 2x4 to the side of my head to get my attention and then straighten me out! I deeply appreciate all you guys that give of your time on these forums...

[TxGreaseMonkey]

It's a possibility. I would look over the connector and wiring carefully for anything that looks suspicious. Check for any possible breaks in the insulation.

[fripco]

You guys are the best! I wasn't able to look at this any more until a couple of days ago. We removed the switch and it nearly fell apart when we opened it. Definite heat damage. We installed a new switch and I think we're set - Thanks again for sharing your expertise!

Alan.

[kitch428]

You're welcome!

[fripco]

AARRGH! I spoke too soon - Here's what happened tonight...

1. I was driving with the a/c on and the fuse blew. I replaced it and it blew within a couple of minutes.

2. New fuse - I continued driving with the a/c turned off, but the blower still on. Fuse blew.

3. New fuse - Continued driving with the blower turned off. Blew.

This seems to eliminate anything to do with the a/c, blower, switch, etc... The fuses seemed to blow tonight whenever I was accelerating from a stop.

You had suggested earlier about checking the integration relay. Is that a plug and play piece? Is the relay the actual fuse block? Would I replace the whole block?

Any more input is greatly appreciated - this is frustrating!

[kitch428]

You will have to replace the whole block. Not a big deal. It will be obvious where the hot spot is on the block by inspecting it carefuly. The blower switch probably caused it.
Go back to post #8 of this thread, read and look at the pdf I attached.

[fripco]

Well, it's time for round 4. I replaced the integration relay and the blower motor relay and it still popped. It seems that all the components have either been replaced or tested. It only happens when I accelerate from a stop - within 2 seconds after I step on the gas.

Could there be some component upstream of the fuse that's sending a surge to the fuse. I'm good with nuts and bolts, but am really out of my element here.

Thanks!

[kitch428]

Sorry to hear this. Electrical gremlins can be nightmares sometimes. It seems that every time the engine is torqued from acceleration this causes the short.
So what I'd do from here is check the engine harness. To do this, first try this from the drivers seat. Set the hand brake, foot on brake, put in drive, and torque the motor against the brake to duplicate short.
If it blows, then we'll do a wiggle test of the engine wiring harness. Most likely where the harness comes off the injector rail and goes into the firewall. The place where it flexes and bends the most.
Try that first.

[fripco]

Well, Kitch - I think I found it! I did what you suggested and tap danced on every wire and component that I coud find under the hood. There are 2 sets of wires coming off the distributor area and feed down to the main wiring harness. I very gently tugged on one of those wiresets and the fuse blew and then was able to duplicate it every time. We exposed all of the wires leading into the harness and couldn't get it to blow. Our theory is that two wires with bad insulation were touching and we separated them. We couldn't find any wire that looked suspect, so we taped it all back together. We'll just wait now and see if it goes into remission.

Thanks again for your expert advice - as always, it's deeply appreciated!

[kitch428]

Cool! A tip to try when you narrow a search like this. I made a short finder by using 2 wires with male ends and soldered a side marker bulb (194 bulb) between them.
I place the 2 wires in place of the fuse and the bulb is used as the bridge. Very low amperage runs through a 7.5A circuit so the bulb is very dim without short.
But if the short is created, even for a brief second, the bulb will glow very bright. Saves on using a waste of fuses.