So last week my a/c speed selector switch was finicky. There would be no air, I'd wiggle it, and it worked again. Anyway today it went out-out. No speeds work no matter how much I switch and jiggle it. I thought maybe it would be the blower since those seem more prone to failure but it tested good by shorting the high speed blower relay red/purple wires together. So I'll get a new head unit because of this issue, the hissing (even with the screw fix), defrost position not turning on radiator fan (weird??) and the light bulb socket is broke on the head unit side of things.

I welcome input on those issues though that's not my actual question. I figured I could bridge the high speed wires every to/from trip to work/home after I start the car just for the rest of the week to have a/c but I realized the compressor also does not engage since this problem started today. 1. Do you think that's expected with the current head unit condition and 2. is there an easy way to get high speed blower/compressor engaged for the rest of the week easily? I'm not sure how dangerous shorting the pins at the accumulator would be in 95 degree heat for 3 days since I don't think it cycles even once on my way home usually.

Thanks!

 

Probably not the control head.

Pull it out of the dash. Follow a lone brown wire about a foot or so in. You'll come to a connector of the stoooooopidest design EVAH. That's what failed. You'll see, it'll be obvious.

 

I remember you posting about that wire connector! I was definitely going to fix that brown wire once I had the unit out. Would the symptom of the connector failure be everything not working except for the radiator fan control? That's the only thing that works. (Though defrost doesn't kick the radiator fan on like I said)

Thanks Sofa!

 

Yes. It feeds power to the whole thing.

The radiator fan is completely separate. It will still work fine even if the control head is removed from the car.

 

Great news thanks! I'll update the thread afterwards so hopefully we'll have another confirmed fix in the books.

 

Ok closing the loop on this one. Got my newish hvac control unit Friday so I pulled my old one out today. The infamous brown wire connector was only about 6 inches in and actually looked ok for its age. It only had some brown imprinting on the plastic where the metal beneath it had pulsed for 27 years. I cut it off and put some solid connectors to replace it. Connected everything else and tested the controls....5 seconds delay of nothing.....and then fan blowing. Ok so, what?

After a lot of wiggling and jiggling I discovered the problem. What was it? The brown wire! Though, not the infamous problem connector but the actual connection to the hvac unit itself (far left if you're looking at the front of the unit). The brown wire connection inside the long connector that plugs onto the top middle back of the control unit had melted itself free over the years and somehow become overly spread at the "lips" that grip onto the terminal on the hvac unit side. The terminal on my old hvac unit for that wire was black compared to the copper color of the rest. The new unit terminal was still copper colored which was a good sign as a replacement. So I scraped the black off of the wire connector, bent everything back tight on it and actually connected it to the hvac unit terminal first (since it pulls out of the connector now) and slid the connector back over it and the rest of the terminals. I may revisit a full repair of it in the future but as it stands now everything looks and works great. Thanks Sofa for leading me to the problem!

Somewhat related, I was amazed at the new unit's lack of vacuum hissing and the immediate mode changes when I slid the top selector switch. It's been so long since I've had that. Even after the bolt/nut fix for the vacuum dial on my old one it hissed all the time and would have problems switching to vent or heat without waiting 10 minutes for it to work or having to find the sweet spot millimeters left or right from where it was supposed to work. Totally worth $100 dollars.

 

I guess that other connection had protected the usual one from going bad by burning up first.

 

Yeah really. On a related note, that exact same connector type was being used on a green wire that was held just above the brown one but it was being held in place against the metal. I wonder what that was for?.

 

Not sure what a single green wire would be, at that point.

If it's not something that draws real high power the way the blower motor does, it probably will have less tendency to burn up. If the wire is a small gauge, it's probably not in any danger.

FYI - the lower 3 speeds of the blower send power to the blower motor directly off of that brown wire. That's what burns up everything in that circuit. The 3rd speed draws around 20A if memory serves. High speed is different; the only current going through the brown wire for that, is the high speed relay coil. Less than ½A. The current that the motor draws in High (about 35A IIRC) comes from a big red wire that runs along the windshield cowl, bringing hard battery to the relay; there's a connector right about directly above the pass side valve cover that burns up the same way as that brown wire one does. Some cars also route the motor ground connection through that same connector, meaning in those there's 2 places under the hood that can burn up. Might not be a bad idea to take a look at that one too.

 

Thanks. I saw your posts about that but for the life of me could not find any connector on the driver's side firewall area. It's possible I did it years ago but already forgot and stuffed it somewhere in that thick bundle of wires. That thick bundle is the only thing over there on my 92.

 

Not the driver's side.

Various cars have had different arrangements for it over the years and models... some have only a red wire, some have some green wires too (AC compressor), and some have a black wire as well.

 

Doh! I misread "towards the driver's side" as driver's side. Thanks I'll check it too!