Well, it's getting cooler here in Vegas so no worries yet!

I tried to use a little Air today, but when I pushed the button, no light and no worky. What's the most probable cause for this "out of the blue" problem?

 

When this happened to me I made the ASSumption it had to be the infamous relay in the control head. So, I replaced it with the RadioShack relay other have used successfully. My sense of accomplishment was shattered when I switched the AC on and still got no cold air.

So, I went up to the front of the car and pushed in the high pressure valve fitting....nothing came out. DOH!!

What I do now with failed AC is go observe the compressor clutch. If it fails to engage when the AC is switched on, I jump the low-pressure and freeze switch plugs. If the AC compressor clutch kicks in then, I pull the low pressure jumper. If it stops running, you know where the problem is. Could be a low charge or a bad compressor. Get gauges. If it continues to run, I pull the freeze switch jumper. If it stops then, it is a bad freeze switch.

If jumpering the low-pressure and freeze switch plugs does not engage the compressor clutch, I test the clutch by applying 12V to the clutch wire (has a connector near the air pump bracket. If it engages then, the headunit has a problem - most likely the infamous relay.

 

On S4+ If you jumper the low pressure switch on the top of the "low pressure switch canister thingy" attached to the side of the reciever/drier and then the cooling fans come on full with a cold engine and the AC switch pressed you know that the gas pressure is low. Doesn't PROVE a whole lot else though.

The low pressure switch that prevents the compressor kicking in is on the bottom of the "canister thingy"

 

When you say "low pressure switch" is it related to "freon" pressure, or is it a compressor cutout like many cars have related to manifold vacuum? (cuts compressor under full throttle reducing engine load)

 

The low pressure switch is mounted on the side of the drier in front of the radiator. It responds to the Freon pressure. I don't think any of the 928s have a compressor cutout like you mention.

Don't run the compressor long when doing this - just a few seconds to see if the clutch kicks in.

If the clutch works initally without any of the jumpers, then there is no need to jump either of the switch plugs. This would indicate a dead compressor or blocked expansion valve or just a low charge.

 

Bill,

Did you have the light in the switch illuminate while you were t-shooting?

 

One other note... I beleive this is the first time selecting AC since I was on the backside of the stereo. Is there anything in that area that I could've hit?

 

Darien-

Start off with the easy stuff-- the fuse.

Then--

In my '89, the switch panel for the AC and the door locks and the dash 'reset' button has a little multi-pin connector on the back, with no real retainer on that connection except friction. If you've been doing anything in the dash near that panel, you may have dislodged the connector. It only takes a little! You can reach the connector if you have radio announcers' hands (wee paws for station identification...) by removing the side panel on the center console. Otherwise, that little panel comes out from the face of the console with some screws loosened.

 

Oh, the light. Not sure how it is fused (if separate from the rest of the instruments). Do what Dr. Bob says. Maybe it is that simple.

 

If your ignition switch is tired, it may not energize the circuit that runs the climate control

 

This sounds like a problem I was having. I would push in the button and it would work until the next pothole (which is about 2.46 feet in the Houston area). The problem was actually one of the wires grounding on the radio chassis under the center console. I found that out after dukin' it out on E-Bay for a replacement control head.

 

Potholes do serve as a useful diagnostic tool from time to time.

 

My '86 A/C blows cold, but I didn't know there was a light for the button. Is it a replaceable bulb?

 

https://rennlist.com/forums/928-forum/312635-using-led-bulbs-in-the-928-fitments-size-etc.html

1. Courtesy lights (doors, hatch, overheads)--39mm, 6 led, festoon bulbs
2. pod switches-- #74 wedge base bulbs
3. shifter indicators on console-- 44mm festoon, I think 8 led. I drew power from cigarette lighter.
4. HVAC control head-- #74 wedge base, wide angle (flat head). Not perfect, because it's a little dim, and provides little light to the sides to illuminate the fiber optic threads for fan speed and sliders. There's a 3 led, #74 from www. autolumination.com that may work better than the single, wide angle bulb.
5. door marker lights (the red squares on the trailing edge)--BA9 bulb

 

My vote is what Dr. Bob said. Just went through this myself when I replaced the evaporator core. That little plug on the back is notorius for popping off the back of the AC switch. Remove the drivers side trim panel to the center console and look/feel behind there. If you were mucking around with your stereo as you said that is probably the problem.

Good luck,
Constantine