924Board.org

[RK924]

The AC hasn't cooled for a couple of years. I had it checked at a sevice station. They pulled it out and tested it and weighed it and reloaded the correct amount, it is R134a. I am guessing the conversion consisted of adding an adapter to pump in R134a and nothing else as there doesn't appear to be anything new on the system and there is no R134a conversion sticker. It still doesn't work and I didn't want them spending my money trying to fix it. After all I have a Maxima to drive when it's too hot and humid; at least I did until two nights ago when it was totaled''. Now I want the AC in my 924 to work.

When I turn on the AC switch the fan comes on but no cold air.
If I am driving and I turn on the AC fan there is still no cold air and the car begins jerking violently. Any idea what's happening?
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81 924 na Weissach Edition #182 - 924COUPE
06 G35 sedan

[gohim]

The ac system in the 924 never worked very good to begin with, and conversion to R134a makes the the system work even less efficiently.

The fact that you can feel the engine run worse when you turn the ac on, tells me that the ac clutch must be engaging.

Make sure that the heater valve is working and is closing completely, otherwise all you are doing is cooling, then heating air, before it is pumped into the passenger compartment. The heater valve Located under the hood behind the engine at the firewall corrodes and often seizes, and will not open or close (stuck open will heat all the time, stuck closed, no heat, stuck part way open, always puts out warm air).

81 and later 924 cars have electronic idle stabilization (black box located above the "ignitor module" on the left inner fender). You say that the car "begins jerking" when you switch the ac on? This would lead me to conclude that the electronic idle stabilization is either disconnected, or non-functional, or the idle speed and idle mixture are so far out of adjustment that the electronic idle stabilization cannot compensate for the change in the idle speed due to the additional load on the engine.

The ac is not going to work correctly, if the engine is not running correctly. While the ac is never going to work like the ac in any later model car, you can probably get it to work better if you get your engine running/adjusted to run correctly.

I would start fixing the problems by replacing the old vacuum lines and any rubber boots or elbows that are cracked and leaking. Then I would replace the spark plugs if they have over 10K miles, or you don't remember when they were changed last. If the spark plug wires look old, or have become brittle or cracked, replace them as well.

Then, you will be ready to test the idle stabilization module, replace it if necessary. The same idle stabilization module is used on some VW Jettas and Golfs of the same period, and you could get one from a salvage yard at amuch lower cost than a new one from Porsche if yours turns out to be defective. When you have the idle stabilzation working properly, temporarily disable it (there is a quick disconnect on the left inner wheel arch for that purpose, or you can bypass it by plugging the two round connectors on it into each other), so you can finally adjust the ignition timing, idle mixture and idle speed.

[dpw928]

Or the bearings in the AC compressor are shot and are about to seize. Wrong oil mixed with R-134 can cause this.

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

[gohim]

dwp928,

Good point, I don't think the electronic idle stabilization has the range of adjustment to overcome an ac compressor in the act of total seizure.

[Ozzie]

For a system to be changed to R134a the rubber hoses and o rings have to be replaced as well as the system flushed out with a cleaning agent similar to white spirits.
This flushes out all the old oil.
New oil and a new drier are fitted along with a new gas charge.
If this is not done then the system will not work properly and IIRC the old oil reacts acidic with the new gas.
The seals and bearings on the compressor could be shot a swell.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[gohim]

I would think that a competent shop would have done all that was necessary for a sucessful R134a conversion. Mechanics don't always tell the customer everything that they do or don't do. And the Member that posted this thread may not have told us everthing that was done to the ac system.

I would also expect a competent shop to test the entire system by after evacuation, and make sure that everything was working correctly after completion of the work.

We all know the original 924 ventilation system is a poor example of Porsche Engineering/Design to begin with. Maybe the ac system is working as well as it can with R134a installed, there is nothing wrong with the ac, and the owner is just spoiled/used to working ac from a newer car.

[gohim]

Oops Double Post.

[RK924]

The a/c blew cool air two summers ago. Last year nothing and I suspected a leak because when I turned on the AC fan only warm air came out. And as I said when I turned on the A/C fan and the car was moving the car began jerking violently - i.e a danger on the road and no control of the speed, it just starts slowing down as it heaves. I assumed the compressor was kicking in and shutting down over and over due to low pressure (what do I know). I took it to the service station who said they would have to evacuate the system, test for what it is and put pack right amount along with a dye. They did for only $120. They told me it was r134a but then the a/c would not even start so they wanted to know if they should pursue it. I said no, forget it, it's 24 years old and I can do without the A/C.

This year I started thinking about it and thought it would be nice to have some cool air in this and maybe I can track down why nothing is starting, not even the fan for the A/C was blowing. I worked on other things and one day while upside down under the dash I decided to replace the fuse (which wasn't popped) for the A/C fan and BAM! it started kicking on. Now I am back at the point of warm A/C and a jerking car. That is all I know about the A/C.

Gohim got me thinking about the middle lever of the heater controls, it does not go all the way to the left so maybe the heat vent is corroded and perhaps the A/C is cool but hot air is overpowering it. But does that explain the jerking? Not really. I will make sure the heater valve is closed, I will look at it today.
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81 924 na Weissach Edition #182 - 924COUPE
06 G35 sedan

[RK924]

It's not the heater valve -- that closes fine. I also pulled the additional fuse box, no corrosion just a lot of dust, I soaked it with electric contact cleaner and replaced all the fuses.

I'll just be happy that only the driver is overheating and not the engine.
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81 924 na Weissach Edition #182 - 924COUPE
06 G35 sedan

[gohim]

To go any further trying to figure out what is wrong, you need to find out what is happening inside the system.

You need to get a ac manifold gauge set so you can monitor the pressure on both sides of the ac system (high and low pressure sides). Seeing the pressures inside while the system is running can tell you much about the health of an ac system.

Since the car was converted to R134a, you can get a ac manifold gauge set with the hoses and the valves you will need to connect and fill the system if necessary for $40 from Harbor Freight.