Ben in Plano, TX

Randall,

The compressor groan only occurs when the AC clutch is engaged. I can hear it when the compressor kicks in - especially at idle where it coincides with the RPM drop and adjust when it comes on. Noise ceases instantly when the AC clutch disengages. It doesn't obviously change in pitch with engine speed. I noticed in the shop manual that the tolerances on the space between the clutch and the compressor (sorry-don't remember the exact terminology) had to be within tight tolerances and I didn't have feeler gauges to measure it. Could it just be a bit out of spec?

Randall G.

Mike....no point in swapping the relays, if the fan won't run in slow-speed with the #3-#7 jumper installed. The fan runs when you jumper 5 to 7 on the relay because it's really running in fast-speed, skipping around the slow-speed power circuit/ballast resistor (taking the path of least resistance).

Next step is to check resistance across #5 & #7. If you don't get close to 1 ohm, something is amiss. Broken wire or connector, incorrectly installed or faulty ballast resistor.

Ben...the only other thing I can think of that would cause the system to groan would be a malfunctioning expansion valve, or some other blockage. But, since your system is cooling fine, I think the compressor is the likely suspect (as you suspect), and the noise is a typical rotating pump (okay, compressor) sound. But, conjecture on my part here. I kinda' doubt the clutch gap is off, if no one has messed with. Though, it wouldn't hurt to check it.

Other than being worn out, I imagine an improper quantity of lubricant could cause the compressor to groan. But, since you had the noise before your self-recharge, this doesn't seem likely. Even when way down on charge, you don't seem to hear of people complaining of noisy compressors (the low-pressure cut-out is supposed to protect the compressor). Though, I suppose there's a small chance having the system professionally serviced--verifying the proper quantity of oil--will cure the groan.

Carrera Mike

Randall,

I'm sorry, my last post above(which I will delete) was written wrong. My data were incorrect. I actually meant that:

With the relay removed and new ballast resistor installed, putting a jumper on the SOCKET between 3 and 7, the fan does run in slow speed. Jumper on 3 and 5 runs the fan in fast speed.

I also did the resistance test between 5 and 7 and its reading 1.5 ohms. So that seems to be ok.

Let me swap the relay to see if one is broke.


UPDATE: I just swapped the relays and sure enough, the fan works as advertised. With the new ballast resistor installed, the condenser fan now runs in slow speed as I turned on the a/c.
So in addition to a bad ballast resistor, the relay is also bad.

I'll get me a new relay tomorrow for the a/c and as soon as I install that, my a/c should be fully operational.

Thank you very much Randall for guiding me through this. I really appreciate it.

~Mike

Arjan B.

Hey, glad to hear it!

Edit....this is Randall again, logged on as Arjan. I'm not used to checking to see who's logged on when I post. God knows my wife isn't logging on to Rennlist.

a18agy

I was fowarded to this thread by Carrera Mike...thanks very informative.
I have a question, is the replacement resistor a Porsche only part ?

Thanks

Alex

mike cap

Alex,

The ballast resistor looks like an OEM part (made specifically for Porsche). Doesn't remotely look like a gereric part you'd find at the auto parts store.

993tt

Since I started this thread I thought I might tell you what happened

I went to the local air conditioning shop and they plugged som stuff in and found that my system was almost completely empty! How this could be I haven't got a clue since I never saw any leak. Anyway, they filled it up and now I'm cool again! They also put some trace fluid in the system so the next time I pull everythig apart they are going to lend me a UV-light so I check where it leaks.

/E

a18agy

Thanks Mike Cap....also thanks to Erik Phersson for starting the thread.

Alex

Randall G.

Eric,

I'm not surprised your 8 year old system lost its charge. I know the charge in my car didn't make it to 8 years. Yet, I can get 2 summers out of a fresh charge.

Did the shop perform a vacuum test on your system? This will tell you if your system has a huge leak. That is, it won't hold vacuum for a significant period.

993tt

Yep, they did a vacum test and the guy said that if there was a leek it must be very small because he couldn't see anything on his meters.

nile13

this question is mostly to Randall, but to others as well.
My A/C is pretty close to ambient at this point. I made a boo-boo - I charged it today before I read this topic. Now my pressure is at about 30 psi, but I only ran at that pressure for 10 minutes or less. Interestingly, the A/C compressor did cycle on and low side line got cold.I will get a better pressure gauge tomorrow and will bleed by pushing the nipple on the low line until I see about 14.9 psi. Is that correct?

Now, I checked the resistance of teh ballast resistor (pins 87 and 87C on teh relay). It's at 12.4K Ohm, so resistor is dead (oil cooler resistior is at 1.1 Ohm for comparison).

Now, can a dead ballast resistor be the cause of the problem? Should I replace it, or should I take R14 out and jump pins 1 and 6? I assume the relay has no other functionality so it can be kept out then? I don't mind doing that if it makes A/C work properly.

Interestingly enough, when I turn A/C button on the fan in the driver's side fender seems to be running and running on high. Still, A/C blows fairly warm air.

Any other ideas would be greatly appreciated.

PS. One more weird thing. Only one of my center vents blows full bore. The other one gives very little airglow. I played with it's wheel and it seems OK. Why?

Randall G.

>Yep, they did a vacum test and the guy said that if there was a leek it must be very small because he couldn't see anything on his meters.

Eric....that's the same thing the shop told me after converting my R-12 system to R-134a two years ago. The charge they put in lasted about 18 months (2 summers). So, indeed, the leak is slow.

Mike....yup, I would shoot for about 15 psi on the low-side. Did you also charge oil with your R-134a?

Rather than just blasting R-134a all over the engine compartment, see if you can find a kit that includes a hose with shutoff valve, without an integral can-tap/check valve (which prevents back-flow), but with an integral pressure gauge. At least then you can direct the discharge into some sort of container (an old milk jug, or similar?). Of course, make sure you don't contaminate the end of your hose with milk while doing so. And, don't forget your gloves, long sleeves and safety goggles.

>Now, can a dead ballast resistor be the cause of the problem?

I don't think a failed ballast resistor/in-op condenser fan will make the system blow completely ambient air. And, it should have no effect at all when driving at speed (natural air flow across the condenser). Though, it surely will keep the system from running as cool as possible in stop and go traffic.

>Should I replace it, or should I take R14 out and jump pins 1 and 6? I assume the relay has no other functionality so it can be kept out then? I don't mind doing that if it makes A/C work properly.

Actually, you need the relay for the #1-#6 jumper to work. Remember, #1 and #6 are only control signals--the relay is needed to route (relay) switched power to the fan. If you do use the #1-#6 jumper, the condenser fan will always run in fast-speed with the A/C. Not a bad thing, having increased cooling of the condenser. But, it is much louder.

>Interestingly enough, when I turn A/C button on the fan in the driver's side fender seems to be running and running on high. Still, A/C blows fairly warm air.

The system pressure may be high enough that it's causing the condenser fan to run in fast-speed for an extended period (instead of cycling, which is what most people see when the ballast resistor fails). And, similar to Ben, your system pressure it probably so high, it won't cool. I once read that being overcharged by 10% reduces the system's cooling ability about the same as being 50% low on charge. Or numbers close to that.

>PS. One more weird thing. Only one of my center vents blows full bore. The other one gives very little airglow. I played with it's wheel and it seems OK. Why?

If you're comparing the driver's side center vent to the passenger side center-vent--with the driver's side flow being much higher--this is normal. Not sure why--e.g., you can shine a flashlight through the vents, and see they're connected. But, this is a common phenomenon. If you want to equalize flow between the vents, you have to throttle down on the driver's side. This will force more air to be passed through the passenger-side vent.

Let us know how things work out for you!

nile13

OK, little update and cry for help:

I blead the system down to 15 psi with running A/C. Took a _looong_ time for some reason, about 10-15 minutes. Very strange.
Now the air is _really_ ambient, while it was a bit cool before, when pressure gauge was showing about 65-70 psi (don't ask). The funny thing is that compressor was kicking in then and is now.

So, tomorrow I'll have the shop evacuate and refill the system. I want to confirm that they should fill until 15 psi is showing at the low pressure side. Anything else I'm missing?

TIA!!

Randall G.

Mike,

I don't have any other ideas just now. Though, I'll add that the shop may first evacuate your system, then charge by weight (and volume, wrt oil), verifying that the pressure is within the specs.

Carrera Mike

Nile13 & Randall G, Could it be the CCU? It's the brain of the a/c system.