'94 960 a/c starts out icy cold then blows hot after ten min

ppcgm · Post by **ppcgm** » 08 Aug 2007, 21:05

It's 100 farenheit here in the afternoons so my car is undriveable at present. When I put it in the shop for the heater core replacement ($860) I told them the a/c would only blow cold for a few minutes but they of course couldn't make this happen. They'll soon be out of customers at this rate and I need a much better manual than this useless thing I bought of Chilton's.

I've see on another forum that there is a relay on the back of the a/c compressor that I can just bypass by plugging the power wire directly to the compressor instead of going through this temperature sensor that will shut the a/c down when it sense high temperatures. Is there any reason to not try this ? It doesn't appear to be low on freon as I tried to add R134a and it would only take a little out of the can.

Also, the car is running warm. It never gets into the red on the gauge but I'm thinking of swapping in a new radiator as cheap insurance against damaging the engine. Is this radiator swap as simple as it was on my 240 ?

danr960 · Post by **danr960** » 09 Aug 2007, 09:13

First, you never want the temp gauge to ever be in the red area, that means you have over heated and most likely cooked your engine. If you mean that the needle moves towards the red zone but never reaches it, yes you could need a new radiator, how old is the one you have, if original, then yes do change it for peace of mind, change the thermostat too.
How many miles do you have?

About your A/C, could be a pressure switch, when your car is still at idle, the a/c is on and it is cooling is your coolant fan running under the hood? It should be, if not your system maybe in need of a charge of freon, or one of the pressure switches in the a/c lines is malfunctioning. Also went idling with the a/c on is the compressor turning itself on and off, cycling? You would hear a click and then the engine may sound a little different.

If the compressor just shuts off, and stays off for several minutes it could be a couple of things, the high pressure switch is activating or is faulty. If the coolant fan does not activate when it should pressure builds and the high pressure switch cuts out the compressor. It could also be that the temp sensor on the side of the compressor is faulty and shutting down the compressor for high heat when that is not really what is happening. So this needs to be ruled out before proceeding.

Have you ever changed the vacuum motor in the dash, if not, you may be getting the vents settings changed while driving, causing the feeling the cabin is warming and all that is happening is the floor vents are being activated, this usually happens under acceleration or driving up hills.

Let us know if anything turns up.

DanR '94 964 332,000 miles (98,000 on the new engine)

ppcgm · Post by **ppcgm** » 09 Aug 2007, 10:11

thanks for the response and the info, Dan ... my '94 964 has 185,000 miles on it and has the original radiator so I'll replace it as you suggest, and the thermostat with it ... the gauge hasn't gotten into the red but it's getting too close to it and I didn't know whether the two might be related

the vacuum actuator(s) show replacement about 50k and five years ago, so I'm hoping they last longer than that, the vents all continue to flow air, but they all flow hot air, all the time, once the car has been driven far enough to warm up the engine

when I get home today I'll run the car up on the ramps and watch the compressor to see if it's cutting in and out, but first I'll have a look to see if I can locate that sensor on the compressor ... the electric fan appears to be triggering as it should and runs for some time after the car is switched off, so I'm inclined to think it's working as intended, though there doesn't seem to be any real pattern to when the gauge goes up and down, which reminds me too much of what our 245 was doing before I cooked the original engine out of it and is why I suspected the radiator because that eventually turned out to be the source of the overheating in that car

what killed your original engine at 234,000 ?

Post by **billofdurham** » 09 Aug 2007, 12:20

Is the AC 'Off' button flashing indicating a fault?

The radiator replacement is straightforward.

Bill.

ppcgm · Post by **ppcgm** » 09 Aug 2007, 14:36

there are no warning lights of any kind anywhere, the red surround on the a/c button glows steadily when I depress the button and goes off when I pop it out, same for the recirculate button

started pricing radiators and the miscellaneous parts I'll replace at the same time in hopes of getting all that done this weekend, when I get home this evening I'll delve into Chilton again in hopes they at least tell me where the thermostat is

Post by **billofdurham** » 09 Aug 2007, 15:55

You don't need Chilton for that. Follow the top hose from the radiator to the engine and you're there. The top hose fits onto the thermostat housing.

Be sure to get a seal for the thermostat. Fit it to the stat before you put it into the housing.

Pity about the blue light not flashing because you can read fault codes if it is.

Bill.

ppcgm · Post by **ppcgm** » 09 Aug 2007, 16:56

ok ... good info, Bill ... thanks for the tips on installing the thermostat, I'll replace all that regardless

but I'm not seeing where there is a sensor I can bypass on the a/c compressor ... all I see is one wire coming from the alternator to the compressor and runs right in the front behind the pulley ... is that the wire that runs through a sensor / relay that I can disconnect to see if that's the cause of my a/c shutting down ? there is a tiny rectangular black plastic component near where that green wire disappears into the front of the compressor but I'm disinclined to start tugging on wires until I'm sure I'm tugging on the right one

one bank's thermometer says 106, the one at the local college says 109, so the car is parked in the drive and we're riding in the wife's Honda ... hmmm

DanR · Post by **DanR** » 09 Aug 2007, 17:22

Yes that is it, there is a temp sensitive contact inside.

DanR

ppcgm · Post by **ppcgm** » 09 Aug 2007, 21:04

yep ... that looks to be the demon ... I pulled at it and the wires don't want to unplug from it but the bracket did bend and let me make air space between the sensor and the compressor housing, that made it work for about 20-25 minutes, then it stopped cooling ... I was running 80mph on the interstate so left it on and cut back towards home, popped the hood and put a flashlight on the compressor and it's not running at all, so I'm betting the little sensor has opened the circuit and isn't letting any juice to the compressor to kick it in ... tomorrow I'll pull on the wires hard enough to either unplug them from the sensor housing or break them and then make a splice to hardwire juice to the compressor and see if that makes the a/c run on 100+ degree days ... thanks again for the help

danr960 · Post by **danr960** » 10 Aug 2007, 11:53

You really won't know though if it is that switch or your compressor is actually overheating. Proceed with caution.

DanR