1988 CV A/C / Electrical Issue

[friskyfrankie]

My friend's AC was working great last week and this week it just stopped working. I have only taken a cursory look at it but the compressor clutch is not operating (haven't checked for power but suspect it won't have any). I see no evidence of refrigerant leaks but I did find the fuse is blown (Fuse 9) and the area, on the fuse box, is almost completely melted! Almost seems like a "short to ground" would be required to do that but haven't looked further. I would think pulling the wires to that fuse and installing an inline fuse would circumvent that issue but is that the only problem? Something had to cause it (I was told a mechanic told him he had seen that before on the car but let it go as everything was working after installing a new fuse). Thoughts on possible causes and repair??

[kishy]

Speaking to the AC clutch circuit, I believe the only things that can interrupt it are the fuse, the low pressure switch, and the HVAC control (e.g. if in an AC mode or windshield defrost, run the compressor).

As for the melted fuse box, that is definitely evidence of a problem. Dead short seems unlikely , but maybe it has had issues popping fuses in the past so higher amp fuses were used, which allowed more current to flow and more heat to develop. The AC clutch coil could have some windings shorted and be pulling more current than the circuit is designed to supply. I haven't seen this happen, but I know it's an issue that can happen with any sort of coil winding - transformers, solenoids, etc.

Maybe give the clutch 12V directly (not using the factory harness to supply it) and measure the current draw. I don't know what's in-spec for our vehicles but if it's something ludicrous like 9 amps on a 10A fuse, that would tell me the clutch coil needs to be replaced (in addition to a functional repair elsewhere to get the voltage to the new clutch coil such as your external fuse idea)

[sly]

If the fuse is blown AND the fuse socket melted like that, it was probably a crusty connection on the fuse itself. That's gonna be a PITA to fix though. I've had this failure on those in-line fuse holders several times and the fuse box once.

[friskyfrankie]

If the fuse is blown AND the fuse socket melted like that, it was probably a crusty connection on the fuse itself. That's gonna be a PITA to fix though. I've had this failure on those in-line fuse holders several times and the fuse box once.

The melting is on the fuse box, itself and that is why I was suggesting replacing that fuse connection with an inline fuse holder. Its been like that, for some time I am told and the AC worked great. I have to see what else is on Fuse 9 and 6 to see if anything else works. The fuses that come out, after blowing are quite hot so I hope it is just at the fuse box. I would think the wires coming into the box can be cut and then reconnected with a fuse holder. Wonder if that will be a PITA? I guess the question will be - is the only issue at the fuse box or is the issue up the line coming into the fuse box?

[sly]

Should just be the connector in the fuse box. in-line fuse holders should work fine. Just know that the ones rated for 30A should not be run with more than 20A for reliability. If you need 30 amps, bump up to a maxi-fuse holder.

[friskyfrankie]

The melted fuse connection (Fuse 9) is stated to be running A/C Blower, Heater and ATC. The spare fuse holder (Bussmann) I have on hand is rated for 30 amps with #12 lead wires. I would think that should be enough but am open to an opposing opinion.

[sly]

that would be enough, but since it is a 30A circuit, best to keep an eye on it or beef it up to a maxifuse holder. I wish those were made with 10AWG instead as that would reduce the heat produced in the connection and use better disconnects. I always pinch the connectors down about half way to completely squished to provide a tighter grip on the fuse that gets inserted into it. The only problem with using the maxifuse holder is the size of the thing and the 8 gauge wire.

[friskyfrankie]

that would be enough, but since it is a 30A circuit, best to keep an eye on it or beef it up to a maxifuse holder. I wish those were made with 10AWG instead as that would reduce the heat produced in the connection and use better disconnects. I always pinch the connectors down about half way to completely squished to provide a tighter grip on the fuse that gets inserted into it. The only problem with using the maxifuse holder is the size of the thing and the 8 gauge wire.

Certainly all good suggestions but I wonder what the gauge of the wiring coming in and out of the factory fuse holder is? Using a maxifuse may then be overkill if they are smaller (which they probably are).

[gadget73]

The blower shouldn't be related to the AC compressor power, or at least it isn't on a Lincoln. The only thing that 30 amp fuse ought to be running is the blower. I once had problems with that fuse, turns out the wire to the blower had rubbed through on the thermactor pipe and randomly popped the fuse. Changed it to apparently some shit one that didn't blow, and it ended up nuking a fuse link while I was driving. That fuse link is all the key-on stuff including the ignition system so it died. I was in some random suburb outside Chicago in a traffic circle. Managed to get pulled over under a street light, found the problem, and cobbled it back together with some speaker wire. Found the damaged fan wiring at the same time and wrapped it up in tape so it wouldn't fail again.

anyway if the blower is dying or the wiring is messed up it eats a lot of current and any questionable connection on the fuse makes a lot of heat. Also make sure its a proper Buss or Cooper or whatever fuse instead of a cheapie no-name. Not all of the generic fuses work as fuses.


as for the AC compressor circuit, there is also the ECM's WOT cutout relay in the mix but I've had a fair number of problems with low pressure switches dying in these cars. If the refrigerant pressure is good, ohm check the switch or just give it a whack and see if it kicks on. if it does, replace the switch. Once they start getting flaky it doesn't get better. For whatever its worth I've had better luck with Four Seasons switches than OE/NOS Motorcraft. Had several of those that were just bad right out of the box. Probably the "Old" part in NOS.

[friskyfrankie]

That #9 Fuse also works the ATC (or at least that is what the Owner's Manual says) so that could be creating the issue? After checking some other items, I could always jump the low pressure switch (I assume you mean the one on the receiver/dryer) to see if that helps. The switch is an OEM that has been in place only since October 2023. For some reason, any aftermarket lp switches I have used ALWAYS leaked. Would be interesting to replace the #9 fuse and then jump that switch just to see what happens. However, either the fuse box itself or something is causing the fuses to get hot as without doing a thing I have replaced them, turned the AC on and they get hot. Funny thing is when I "ohm them out" they test ok. Not certain what to make out of that!

[gadget73]

bad connections or excessive load. It should not be getting hot, something is wrong.

[friskyfrankie]

bad connections or excessive load. It should not be getting hot, something is wrong.

Agree completely. Funny thing is (well maybe not if an electrical issue is concerned) is that the AC was working perfectly just the week before. Now the trick is to find the offending part.....