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Thanks for this write-up. I'm working on an AC issue right now. I have no condenser fan running up front with the AC on, and the compressor will not engage. If I'm understanding correctly, this means I likely have low pressure? I have tested the relays/fuses and they appear to be good. I had a can of refrigerant from another car so I stuck it on the low side to use the gauge. It shows 14psi on the low pressure side. I know they aren't exact but I feel like its probably within the proper range.
How do I know I don't have a bad fan ballast for the condenser fan? Because the compressor is not coming on?
Thanks, this has been a huge help so far. Florida summer in a black 993 with no AC is brutal!
My AC works great and so does my heat, and i have tested the fans on both sides of of my 1992 964 Turbo and they also work great, , but when the power to the CCU cuts out, and none of the controls work, NO power what so ever except for the back lights on the face, NO AC, NO Heat, NO fan, then a few minutes later everything works great, ??
I pulled the CCU out and cleaned the contacts and everything is plugged in as it should,
I also forgot to mention that when the CCU power goes down so does the power to my oil cooler fan and air conditioning fan... bad ground ? do they share so sort of wiring and where would i find it ?
Please inform me on this, and how to get to the connections. I'm new to the 964 chassis and its electrical system. I look forward to learning
My first plan of attack my intermediate working CCU,
1 check all the fuses 1, 17, 28 and 36. 2 lift the fuse box and check for any lose wires, 3 clean the the connection from the ground strap to the chassis, 4 clean the ground connections to the chassis behind the fuel gauge, 5 check for a strong ground on pin K 1. 6 check for continuity. between pin K 1 and G18 on the CCU, 7 check for 12V on pins K2, G17, G29, G35,
I don't plan on checking the oil cooler sensor or the evaporator sensor or the AC FAN sensor because they all work when I have power to the CCU, which is 75% of the time. because of that I'm assuming it's not my relays. I also jumped the the relays and the fans on the AC and Oil cooler come on only when there is power to the CCU, but when there is no power to the CCU jumping does no good.
If I don't have a strong ground, I'm thinking of running a wire from the battery to the chassis ground connection behind the fuel gauge, I'm assuming that the CCU harness gets it's ground from there, If any one has experienced this before, please chime in
At a glance the pins on the harness look fine as does the wiring, Let the fun begine
Hi Brian, what would be your recommendation for a shop proficient in 993 AC care in the Washington DC area?
Thanks - and thanks for the amazing posting back in '07
Nando
Hi guys. This is a great, informative and thorough thread. My problem though is a different variant. My AC compressor runs continuously, even if the AC is switched off. The Porsche mechanic (Porsche Melbourne) has tried different CCUs and still the compressor runs continuously. So the CCU does not appear to be the issue. I understand there is no shorting issue either. Any ideas that will help with the diagnosis would be much appreciated as my car has been with Porsche Melbourne for well over a week now and they are somewhat perplexed. Anything that can speed up the diagnosis or any similar situation experienced would be much appreciated.
^^^I know it sounds almost impossibly simple and maybe low probability, but did they check the AC compressor relay located in the fuse panel on the drivers side of the engine bay? Might be stuck "on". EDIT- Pulling the compressor relay out should stop the compressor from operating. I don't know if that would or wouldn't be a sufficient test in determining if that is your problem, but it may at least enable you to temporarily stop the compressor from operating, if needed.
Also, there is a chance that your battery has a yet-undetected fault in it, which can lead to all sorts of weird and seemingly unrelated issues. For 6 months, I had all sorts of electrical anomalies (including AC and other climate control switching issues) until one day the battery died a sudden death and the replacement battery solved everything. Later, I mentioned this to a friend who also happens to be a very good mechanic at a Porsche dealership and he said that he has come across that on occasion at the shop as well as on his Ducatti. The battery presents the correct voltages at rest and while engine is running, but ultimately has some kind of fault in it. I did a write-up about it on this forum a few months ago.
My car has never cooled lower than maybe 48 degrees no matter the inside fan speed. It has done that since I bought the car in 2000. Never changes, so I don't think I have a leak.
Now that my compressor or its clutch is making ugly noises at 70K miles, and will be replaced, I am trying to find a way to get the inside vent temps down to the high 30s if possible. (desert duty, global warming, etc....)
My compressor cycles on and off in fairly short cycles, so I am thinking that the temp sensor may be at fault - plan on replacing it along withe expansion valve and receiver/dryer.
Will post results when the job is done in a few weeks.
The compressor normally cycles in 10-30 second intervals with 20 degC ambient temperature. The 964/993 A/C specification and temperature sheet is shown below.
You might have a problem with one or more of the flap servos. A mixer servo could be stuck in the open position, letting heated air from the engine overshadow any A/C cooling . See here for a DIY test procedure.
Cheers,
Tore
I'm currently driving through the Southwest where it is 118F(48C)! The A/C blows cold and works well on the normal settings (small snowflake) - we make our first stop in Baker, CA for lunch and it is hot! We get back on the road and I put the MAX setting on. The car blows cold air but the blower doesn't stay consistently on. I notice that it fluctuates when I hit bumps on the road or when I really put the car under load when accelerating. Am I correct in thinking that this is a resistor connection or some other electrical connection feeding the CCU? Far from home so I am thinking about just taking it to the dealer - if this fails over the next few days, I'm toast...(pun intended)
Thanks!
Originally Posted by Don Magee
Outstanding effort.
Maybe I missed it in the "inside airflow issues" section, but I have the fan speed vary from low to high randomly occasionly. For example if the ac is on and the fan speed is at the second mark, all of a sudden the fan goes on high for a few moments without me touching anything. Curiously, it does not do it if the recirc button is activated. Any thoughts?
In any event, this is a very impressive post.
Using the A/C max button will set to minimum temperature, maximum fan speed and Resirculation on. If you have a vacuum leak, the resirculation flap will close when you accelerate, often with a whomphhh sound, followed by wheezing when the fans try to draw air through closed flaps. The drastically reduced air flow can be experienced as fan failure, but it is not. See this web page for details, chapter Vacuum operated resirculation flap
Cheers,
Tore
Thanks Tore. I will check again in the morning but I don't seem to get the Whoomphh sound with the fan still running. I sense that it is electrical (or electric signal) in nature as the fan cuts out completely. It happens on the occasional bumps on the roads under constant throttle as well.
04-25-2017, 08:11 PM
