rickjaffe

took the car in for a belt and water pump change.
when I got it back the a/c wasn't working. It was working perfectly before

a/c light goes on; fan engages, has a drop in voltage, but the compressor doesn't come on. Checked coolant levels, ok.

shop said only thing it could be related to in what they did was the cap or wire in the front of the engine above the compressor. They have to swing the compressor to get to the belt or water pump. But upon inspection, it was connected.

they checked fuses; they're ok.

the power is not coming out of the ecu to engage the a/c clutch

they can't tell after this initial check what the problem is, but it isn't from the front of the engine. Something electrical, possible bad switch, bad ecu or something.

Any ideas?

any easy bypass temporary or otherwise? maybe by pass switch, keep a/c on always?

only thing they're recommending is to start digging into the system; might be something in the pod; wire, switch who knows.

Looking for a cheaper solution or fix than paying hundred plus an hour indefinitely until they find the problem.

hacker-pschorr

Is the A/C belt on?

Mark

They broke it - they should fix it!

rickjaffe

not sure I can prove it. don't have an ideal of a connection between a water pump and timing belt change which takes place at the front of the engine and the electrics which run the a/c unit.
that's something I'm wanting to know.
seems pretty conincidental to me, and I don't believe in coincidences but I don't have enough of a mechanical background to see how it could have happened.

rickjaffe

they checked all the easy stuff. connected wires. they think it's back from the compressor; power isn't coming out of the ECU. If it were, then it could be a wire to the compressor, but since there's no power from the ECU, seems like it has to be switch or ecu related; ie before it gets to the wire to the compressor, since that's not live as we speak.

John V

Just a thought - isn't there a thermistor in the alterator duct that plays a roll in the climate control function... could that have been damaged/unplugged by moving the alt? Bad compressor ground or even a slight refrigerant leak that may have tripped the low limit swtich perhaps?

Garth S

You can easily test the AC clutch for engagement by jumpering +12v fused to its connector once opened .... where you looked for a 12v signal from the AC controller head on the other end of that same wire that crosses the right front..
With everything connected, do the fans come on when the AC is switched on? Are other fan operations normal? What I'm getting at are possible other interlock functions that may not allow the AC to energize: while not too familiar with the ac system, I'd check connections on the top manifold switch, right front mounted fan controller, lower right rad thermo switch, right fender lip 'close hood' switch, etc ... anywhere a wire connector could have been touched.

rickjaffe

refrigant levels normal; rest not sure about

928Quest

Single wire back to compressor, towards front of compressor. Mine used to fall off all of the time and had same symptoms. Not easy to see or to reach.

auzivision

This one has already been discussed at length here:

https://rennlist.com/forums/showthre...ferrerid=42802

It does appear to be an obvious and easy fix. If the ‘ECU’ isn’t sending out +12V it’s the famous failed relay syndrome. My guess is the connection was cleaned (intentionally or unintentionally) during the R&R of the A/C clutch wire and it improved the circuit (i.e. lowered the resistance). However, this improvement pushed the relay over the top and it failed.

I really don’t think you have a leg to stand on stating it worked going in and now it doesn’t unless the wire was not connected, connected incorrectly, or severed. Follow the wire back towards the firewall to the freeze sensor and check there for +12V. If it present there then you might have something. Otherwise, I would quit trying to place blame and just fix it.

Sure a jumper or switch can easily be added. Just use the +12v found at the jump-start post and wire in a switch.

auzivision

It most likely would if ignition key in the run position and the A/C button pushed, but I doubt they would be working on the front of the engine with the key in the ignition.

The relay inside the HVAC control unit is only rated for around 3 or 4 Amps. The sad thing is the control unit it self is protected by a much larger fuse (IIRC 20A). So in other words the fuse doesn’t protect the internal relay.

The other sad thing is the A/C clutch often draws more than the rated amperage of the internal relay. This is why this is such a common problem and it’s often discussed on this board.

Many people opt to put a secondary relay external to the controller to prevent this from happening. I will be doing this to mine before summer is here.

auzivision

Push the temp selector to full cold and the system will ignore the outside temp sensor all together. So you can take that out of the equation.

The fact that the fans come on most likely eliminates the A/C switch. The drop in voltage is caused by the in rush current energizing the fans. So you can take that out of the equation.

There are three possible causes for power not to reaching the clutch:

1) Power not coming out of the back of HVAC controller (most likely cause is on the internal relay and I would place my money on this)
2) Freeze Sensor
3) Low Pressure Sensor

Number 2 & 3 are in between the controller and the compressor and can easily be jumpered to take them out of the equation.

rickjaffe

after some diagnostic, they determined that the ecu had failed, and that some of the wires leading to it were corroded. No connection to the bad coolant resorvior which had been leaking

they replaced the ecu, and replaced and cleaned some of the wires.

picked up the car yesterday morning; a/c was working ice cold.
drove about 3 miles to have breakfast. When I started it up afterwards, no a/c; same issue; a/c light is on, but only ambient air is blowing.

drive it right back to the shop. they're still looking.

btw: it's not so much about blame as causation, and diagnosis. As I said, I'm not a big believer in coincidences, but they surely happen. The point about their causing it is more that what more would they have to retrace if it had been related to the water pump and timing belt. They say it's only the wire or cap above the compressor. If so, and that's connected then there is no connection. my orginal question really was what else could have been mistakenly cut, shorted or otherwise interfered with in the process of doing the timing belt.

seems pretty clear to me now that while the immediate problem might have been a failed ecu, there was probably something which made it fail, last time and maybe this time (assuming it failed again). But I still come back to the coincidence thing: what are the odds that the very first time I try the a/c after the t/b belt change it fails, when it had been working properly before. Based on the responses, it does not appear that there is any explanation of a connection, but it still seems odd to me as a non-mechanic.

dr bob

Rick--

The relay in the control head is undersized, and will give you those symptoms when it's on its last breath. Visit any of the tips sites for some diagnostics and a DIY fix option with a replacement relay. Option is a rebuilt or new control head in the console if you don't want to do the relay fix.

docmirror

Rick, it's most likely the relay in the head. I can fix that for you, see Roger at 928sRus for details.