Here in the Phoenix area we hit triple-digit temps about 10 days ago. Son o'Gutz has been doing fine in the AC compartment for a couple of years now and I was just thinking about that when the cabin started warming up on my way home one day. Crap! Recharge time? So of course I went to open the windows, and nothing doing... sure enough, the windows are protected by the same fuse as the the AC. I recalled Art B's comment about passive-aggressive Swedish engineers...

After confirming that even fresh fuses would blow, I disconnected the line to the AC clutch, and the fuse still blew. After a couple more checks, it appears the relay itself is the problem; without the relay installed, the fuse won't blow. What's odd is that the relay coil terminals show open on the meter, which means they shouldn't draw current.

Anyone else run into an AC relay problem like this?

Agree with Sean.

The relay could* do it, but the likely problem is out under the hood. That green wire runs to the low pressure cutout and the fan relay. Try removing the connectors on those to get closer to the culprit. The wiring diagram is a big help: 240 ac notes

Another hint: Use a backup light bulb or similar instead of a fuse to troubleshoot the short, saving on blown fuses.

* have seen upside-down relays filled with rust from water following their wiring
--
Art Benstein near Baltimore

We never really grow up, we only learn how to act in public.

Hmmm... now you and Sean have me scratching my head. But I do appreciate the help!

The initial symptoms are blown fuses. With the compressor clutch wire disconnected, it still blew fuses when the snowflake switch was turned on.

A couple of things I think can be ruled out. First, the pusher fan (in front of the grill) works fine when powered directly. This is controlled by a relay (clipped to the ign coil) in series with a pressure switch in the refrigerant line near the condensor, but I have jumpered that switch so the fan works all the time with the AC. So unless the relay coil is drawing

The pressure switch on the dryer is isolated from ground. I checked the green wire from the dryer to the clutch, and I see over 200k ohms - not zero, but a pretty poor path to ground.

The other line from the dryer (gray?) shows about 88 ohms to ground, which I think could be the lamp in the dash switch.

Maybe it's too hot for me to think straight. Any suggestions on what else I ought to check?

"Maybe it's too hot for me to think straight. Any suggestions on what else I ought to check? "

Probably the method is what needs checking. You're not going to find the fuse blower poking around with an ohmmeter, or by focusing on components that might need replacing. The short is not likely to be hard and fast: Does it kick the fuse if you just turn on the ignition and wait for the delay (10 sec) to cycle? Probably not, because the short is on the other side of the low pressure switch.

Look for wiring damage. Insulation worn through by vibration. It won't necessarily show up on your ohmmeter, because it won't be actually making contact when you've got your head under the hood. The better method with shorts is always divide and conquer. Replace the fuse with a 21W bulb, and remove components in the path. Start with those I suggested earlier because it is easy -- the low pressure switch, for instance. Just pull the connector off. Does the light come on then? No, 240K ohms is not going to blow a fuse. Guaranteed. Neither is 88 ohms.

Here's one alternative to kicking fuses while looking for a short.




--
Art Benstein near Baltimore

A grenade thrown into a kitchen in France would result in Linoleum Blownapart.

Thanks for keeping me on track, Art.

I like the test lamp idea; I've used one for years but the low-watt bulbs I used wouldn't be much better than a fuse, so now I have a freshly-made one that looks remarkably like yours. Finally found a use for a dual-filament halogen lamp with one filament burned out.

Armed with the new test lamp I proceeded to work from the compressor back to the dash, unplugging each component in turn; no change, and the AC works fine. Then I realized that yesterday's trouble-shooting may have unknowingly removed the problem. Recall I've bypassed the low pressure switch by removing the connector and jumpering across the connector terminals. When I was poking around yesterday, I unwrapped the connector, checked the jumper, then re-wrapped it all and re-secured it with a tie wrap. I suspect the problem may have been with that arrangement. Although nothing looked arced or corroded, the spring clip on the connector was exposed and it may have contacted the jumper and allowed a short to ground.

So all's well for now, but if the problem recurs, I'm better armed and educated to diagnose. Thanks for the help!

I do not currently have a wiring diagram handy, Smitty, but is it possible that it is not the relay itself, but the wiring that it energizes which is blowing the fuse? Perhaps under hood wiring on which the insulation has finally failed?