prescott

Driving home this afternoon I turn on the AC as usual and everything works as normal....cold air. Stop for gas. Startup, no fan (on max), no AC (light is off, button is pushed in). I think, crap! 2 miles later, after turning off fan and AC, multiple on off with those, suddenly! it works again. Get it home and shut down. Turn back on. No fan on any setting except defrost (max)! and no AC light either on or off.

I pull every fuse labelled AC, fan. All good. Deoxit all and reinstall. My AC was serviced less than 12 months ago so I assume that within 2 minutes my compressor didn't just die. It must be the AC relay right?

Where is that relay? Anybody got a photo so I know where to replace the D@m# thing!?

Brian

The Forgotten On

The relay is in the head unit and in order to be replaced, the head unit has to be rebuilt.

It could very easily be the blower pack inside of the system that controls the blower speeds, as you have it working fine one minute then acting up the next I would assume that is the issue.

Search "Magic Blower syndrome" for more info.

prescott

I'll check that thread! Thanks for the help!

Brian

Bertrand Daoust

You can try this:

https://www.google.ca/?gws_rd=ssl#q=...lower+syndrome

Lots of info.

dr bob

The relay in the head unit manages only the compressor clutch and the signals to the various brains to tell them that the AC is on. Your symptoms point to a couple other relay possibilities on your '88 car.

I'd replace the Fresh Air Blower Relay at position X, and check fuse 17 and the fuse holder. The relay is a standard 53b type. It's activated by several options in the control head, so it might also be worthwhile checking to make sure the "edge" connectors that slide on the rear of the controller itself (front face as it is installed in the car, front is front of car), accessible in place by removing the left (driver's) side panel from the center console.

I'd also replace the X-bus relay prophylactically in position IV, since it indirectly switches primary power to the control head, and "relay IV" shown on the wiring diagram but location not identified, which is switched by the X-bus relay and actually supplies the power to the head via fuse 6. Alan may have a better clue on this "relay IV" at coordinates 38F on the diagrams. All these relays are 53b type.

If you haven't done so already, the LH (at XXV), EZK (at XVI), and fuel pump (at XX) relays are the same 53b type, and are the ones most likely to strand you. Easy WYAIT to replace the relays for the AC system.

Buy good relays. Our supporting vendors have identified replacement relays that are durable enough for 928 service. Most local parts places sell the lowest-cost pieces they can find without much regard to quality, so I tend to use them only as a stopgap when the "real" parts are on their way.

Alan

This is NOT a likely cause - the blower resistor pack only controls speeds 0-3 - speed 4 is direct drive from the blower switch.

Alan

Alan

Relay "IV" is the X-Bus relay in position IV. I guess someone got confused in the labelling while doing these diagrams and swapped position for ID... one of many minor mistakes.

Make sure the head unit (main PCB) connector is fitted correctly. Also when you check fuses don't just look at them - test with a DVM. Visual evaluation can often tell you that they are blown but it can't really tell you that they aren't...

Alan

Randy V

Had the same issue last week.

Wiggling the associated relays indicated Relay X (type 53) was balky. Replaced and all is good now.

dr bob

This was a head-scratcher since the coil is energized by the X bus per the drawing. The connection points on the CE overview show only the fuse 6 connection, which would otherwise lead me to believe that this is not the X-bus relay.

[still scratching...]

prescott

Here's the update. Battery disconnected. Replaced both relay X. reconnect battery and restart. No change. Disconnect battery. Replace IV. Reconnect. Start. No change. Blower blows full blast on defrost, nothing off of defrost on any setting. AC light does not come on, compressor does not engage when "on". Fan does not work in any position but defrost. I'm going thru the fuses again. I checked them yesterday with the volt meter before reinstalling, but with the new relays who knows? Things that make you go hmmmmmm.

prescott

Disconnect battery. Replaced old fuses with new fuses from Roger in 6, 13, 17. Tested all old ones, they are mildly black corroded but test ok. Reconnect. Restart. No fan on any setting. Turn to defrost, fan blows full blast hot. Push AC button. No light and compressor does not engage. Wondering if I have a blown relay in the AC unit itself. I looked at Dwaynes write up today and it looks a little tricky! Any ideas?

prescott

BTW, I replaced all the fuel system relays after buying the car. Got stranded once without replacement 53 relays, but NEVER again! I have 4 in the glove box just in case!

Alan

The CE representations (inside the dot/dash boxes) on the individiual WD sheets do not show ALL connections to CE components that are shown there - only the ones that are relevant to functions on that sheet.

So for example in this case the CE panel diagram itself (page 11) lists the relay IV 87 connections to Fuse 6 (shown on its own in WD page 5) on and to the fog lamp relay VIII 30 (shown on its own in WD pages 1 & 2). Neither of these references the other content.

This can be quite confusing, and is a reason why you always need to x-ref to the CE page listing to determine all possible connectivity within CE.

Alan