andrew911

I have recently replaced my HVAC unit with a used/"refreshed" HVAC CCU due to battery drain issue- seemed to do the trick as car was holding its charge, and that unit may not be related to my current situation. In the past few of weeks, I have noticed my car isn't holding its battery charge as long as before (I generally only use the car on the weekends), and after about 1 1/2 weeks of sitting, I needed to jump start the car (I didn't have the porsche battery maintainer plugged in, which I use when the car will sit for a month or longer).

Anyway, I sat in the car when it was off last night and noticed that every few seconds I would hear a clicking sound that seems to be coming from the dash board area. It almost sounds like what I would think is a relay clicking or something. Does anyone have an idea what this clicking noise is? Could it be a motion sensor for my alarm (which I didn't have armed when I was sitting in the car, and I don't leave armed when the car is in my garage by the way), or is there maybe a relay hooked into the CCU for the HVAC that could be turning on and off and causing my battery drain?

Thanks in advance for any help you can offer!

Andrew

Rocket Rob

Was the CCU change the cause of the clicking? Have you tried removing the new CCU to see if the clicking goes away? As far as I know, there are not any relays within it.

andrew911

The sound seems more to be coming more from the gauge area than the CCU itself, but I haven't quite pin-pointed it yet. I didn't know if the CCU could have been related, or the servo motors that move to allow heat in have something to do with it- are there relays for them?

Currently my heat doesn't work, and the place that sold me the CCU is mailing me a relay to change to allow the heat servos to open (when I tried to put the heat on, the A/C fan motor behind the headlight was cycling on and off, and the servo motors were opening and closing) I don't know which relay it is- he said when I get the relay in the mail, I'll recognize it and know where it goes (so much for customer service). He said this is what was causing my problem with the heat. I hope its related so I can sort this out- very strange....I feel like my porsche has lucas electronics in it, not Bosch

Adrian

Dear Andrew,
I would love to know where you are going to plug this relay in. There is no relay for opening the mixing chamber servo valves.
The servo are kaput this is why they are not opening.
The ccu power circuit is timed via the electrical distribution system. I have no idea what coul dbe clicking. The only relay I could think of is the gong relay. It is activated by your door switches. If you have a 89 or 90 model it could be your central locking control unit. I had this problem. Fixed it myself.
Ciao,
Adrian
964C4

andrew911

Adrian- I'm as curious as you to see what this relay is going to be for. If there's anyone who would know about it, its you- so I don't feel too confident.

About the servos- its strange, I took off the cover under the trunk to observe, turned on the heat and watched both servos in parallel open about half way then close, in an endless cycle with the external A/C fan switching on and off in the same cycle. I would think its odd for both servos to go at the same time, but what really gets me is the A/C fan going on and off- its like the car is possessed! Does this sound all inter- related with the servos being bad or CCU being bad or something? I checked the operation of the other servos (the ones that direct air to the windshield, feet, etc.), and they work find. The A/C works fine as well- its just the heat that is doing strange things.

Any imput is appreciated- I'm all ears! Thanks!
Andrew

Adrian

Dear Andrew,
Well first of all you have to have heat supplied to the mixing chamber servo valves. Is your rear blower fan working? Second you have to select heat so turn the temp **** up to the red dot and make sure the rear blower fan is working. If the rear blower fan is not working you have to fix this first.
If the fan is working you should have heat being supplied to the front. Check in the wheel arches to see if the heated air is being dumped overboard. This would indicate a stuck open differential pressure valve.
Another check you can do is turn on the defrost. Make sure the air coming out is heated.
You will have to go step by step on this one. The condesner mixer fan is a two speed fan. This may be a related problem or a separate problem. We need to see. One step at a time starting with the rear blower fan. The fuse and relay are in the engine bay electrical panel on the left. I do not spend all day on the forums so it might be best if you emailed me if you want faster responses. adrianstreather@rennlist.com will get me.
Ciao,
Adrian
964C4

andrew911

Adrian- The servo motors were cycling to a partial open and then closed stated, every few seconds (with the outside A/C fan). What I did to check if I was getting heat was pop the connecting rod off the servo motor, and pull the rod out to open the heat valve for the driver's side. Someone was in the car and felt the heat come on at this point, so I confirmed I am getting heat. (We switched places and I went in to confirm hot air was coming out- it was definitely hot). I will see what relay the place that sold me the CCU sends me, and e-mail you when that fails to fix my problem (which I think it will ). I'll also post the progress here for any interested readers...

Thanks-
Andrew

Adrian

Dear Andrew,
The ccu controls the servo motors directly. There is no relay. Your experiment proves to me that both your servo motors are kaput (not uncommon) or your CCU is failed. Either way installing a relay where one is not fitted is not going to help anything which I feel you already understand.
There are only three relays involved with this system directly 5 if you count aircon and rear window heating.
Oil cooler fan relay (2 speed package)
Condenser mixer fan (2 speed package)
Rear blower fan (2 speed package)
Aircon compressor
Rear window demister
Ciao,
Adrian
964C4

PS: What is the part number of the ccu they sent you?

andrew911

Adrian- first off, I will say I think I figured what the clicking noise was I mentioned earlier- when I'm in the car when its off and I don't move there is no clicking, but once I move my hand in the car or make some type of movement, there is a quick 2 clicks- it must be a motion detector from the aftermarket alarm system, so that's OK with me.

I do have 2 questions for you though regarding the CCU/ HVAC:
(1) Would both of those servo motors cycle back and forth together if they were both bad, or would they not move at all?
(2) I speficied that the unit I needed was the part number with prefix 993 (the updated CCU) and "00" in the number. The shop that sold me the CCU said they would make sure it was an "00" unit and not the "01" unit which is used for the 993. Oddly enough, the unit did not have a part # sticker on it (it was a used and supposidly tested unit), which made me suspicious. Would the "01" unit still control the fan speed, air location and A/C fine, or would it not work at all in the 964? Or is it just a glitch that using the wrong unit would cause the weirdness I'm experiencing with the heat? Does it seem the A/C fan outside the car would cycle on and off if the was the wrong CCU? I don't see the relay listed in your list in the prior post above, unless its the "condenser mixer fan".

I didn't think anything would really work with the wrong CCU, but it may be the case that the place intentionally (if they didn't have any 993 prefix "00" units for the 964) or unintentionally sent me the wrong CCU unit.

Thanks for your help with this- I know this seems to be a specific case to my car, but I hope some others get some insight into this topic they can use if they have trouble with their HVAC/ CCU.

Andrew

Adrian

Dear Andrew,
Answers to your questions,
1) Yes quite common. They should not cycle they should modulate. When you select heat they should drive and stop. This allows heat to flow and then they will modulate around the first drive position to keep the hot air and cold air mixed to provide the correct temp. This is controlled by the mixing chamber temp sensors whcih I have never heard of failing.
2). Again this could be a yes. I know this is hindsight but you never accept a part without a part number. The 993 -01 units cause horrible things to happen to the 964. I have a number of examples. Without a part number you cannot be sure what you have and you may actually not have a real problem just the wrong part number ccu. It would partially work but the earth connections are not correct on all the pins for the 964 and this causes immense problems. The other issue is that I do not know your model year. The 993 units will not work in a 89 or 90 without wiring mods carried out. If you started with a 964 -00 unit then a 993 -00 unit will not work either.
Ciao,
Adrian.
964C4

andrew911

I have a 1993 964. The unit I requested from the shop was 993 659 047 00- I speficied with them NOT to send me a 993 659 047 01 unit. I am not home, so I don't know the original number on the original CCU from my car right now, but being as my car is a 1993, I think the part # above would work. You right about using a part with no number- and it threw up a red flag when the unit I received had the sticker removed.

Anyway, the two heat servo valves continually open and close when I turn on the heat- without me adjusting the temp they will keep opening for a second or two then close, and no heat ever gets in the car. I'll have to play with this more, and I'm going to call the dealer that sold me the CCU once I try this relay he's sending me.

I could believe it that my heat flap servos are bad, I just can't figure out why the A/C fan outside is turning on and off as well though- that's what's making me wonder if the whole problem is with the CCU...

Adrian

Dear Andrew,
The servos should not cycle like you desribe. They are not opening the mixing chamber valve enough to let the heat in. It could well be the ccu. Is the frequency of cycling of the servo valaves the same as the fan. If it is I suspect the power supply circuit of the ccu. I might point out that my faith in refurbished and repaired electronic units is very low. Especially Porsche 964 stuff, in fact anything Porsche. The simple reason being that there are NO service manuals for this stuff. Bosch do not even offer a repair service anymore. Haven't for years actually. I wonder how people can actually claim they are fixed when there is no documentation. Well none I have seen anyway.
Ciao,
Adrian
964C4

andrew911

Adrian- the cycling of the two servos is at the same as the A/C fan motor- you may have hit the nail on the head with the supply circuit of the CCU being the problem. What can I do to fix that- does the whole unit get rebuilt again, or do I just need to buy a new CCU? The reason I didn't buy a new CCU initially was that the Porsche dealer wanted something like $1,200 (US$) for it vs. $350 I paid for this unit. Of course as we discussed earlier, the unit I have could be the 01 993 unit and that could be the problem too.

Once I at least give this relay they are sending a try, I will contact these people and see what they can do for me assuming that doesn't do the trick- maybe they can send me another unit to try or give me money back....I agree with you that refurbished electonic units like this are a little shaky, but to save $850 I was willing to give it a shot anyway

Thanks for your help Adrian by the way, as I struggle through this project!

Andrew