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COMPLETE A/C Diagnosis

 
Old 04-24-2010, 08:12 PM
  #46  
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i am speechless ..

a masterpiece ..
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Old 04-25-2010, 04:48 AM
  #47  
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Zingari, I suspect you have a leak in the evaporator. Take a close look at the rubber drain hose underneath between the front wheels to look for dye. If the evap's OK, say a prayer that it will stay so. Replacing it is not for the faint-hearted: http://www.p-car.com/diy/ac/
Regards,
Tore
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Old 04-25-2010, 07:17 AM
  #48  
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Tore - That is my worst fear and will take a good look.

The P-car evaporator DIY looks do-able as it doesn't rely on any specialist tools - just a damn good memory, plenty of time and patience. And at least if I do it myself I know that all the parts will be going back OK.
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Old 05-03-2010, 10:03 PM
  #49  
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Brian your COMPLETE A/C Diagnosis is one the best I have seen this is going to help a lot of us with our 993. I thank you for such nice work. I also have a 1989 964 do you know what the high high pressure an the low pressure should be on a R12 system? Again Thank You for your help on Rennlist. Vernon
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Old 05-06-2010, 01:01 AM
  #50  
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My A/C compressor stopped working a few weeks ago, and using Brian's comprehensive diagnosis, along with several of his other threads from years back, I've traced the problem down to an open circuit at the 3-level pressure switch. Once I get a system pressure reading tomorrow, I'll know if the issue is actually low system pressure or a faulty switch.

In any case, during my diagnosis I checked the resistance of all of the sensors that feed into the CCU against pin G18, the common ground for the sensors. Everything checked fine. I noticed one of Brian's comments was to check pin G18 to ground to ensure that it has a strong ground connection. What I found was that G18 had no connection to ground at all. This really bothered me and I spent hours looking at the wire harness on the car in different locations, checking my crappy scanned copy of the wiring diagram, and searching the internet to see if I could figure out where the ground point for this harness is. Finally after a while, I noticed a small arrow on the wiring diagram that seems to indicate that pin G18 is an output from the CCU (this arrow is on the line from G18 down towards point a point labeled 2 on the wiring diagram). This lead me to believe that G18 provides a ground to the sensors from the CCU, rather than G18 at the harness itself being connected to any ground on the harness side. I confirmed this by checking that the case of the CCU indeed is strongly grounded when mounted into the dash. Apparently the sleeve that the CCU mounts in is grounded. In any case, if my understanding is correct, G18 provides a ground to the sensors when the CCU is connected and installed. When connector G is not connected to the CCU, the sensors are not grounded, and if you check for a ground at pin G18 on the connector, you won't find one.

If someone can confirm that my conclusion is not correct, please let me know. Otherwise, for anyone going through Brian's diagnosis, know that you cannot check for a proper ground by checking G18 on the harness. A good way to check that the CCU itself is grounded is put the removal tool (whatever you used, nail or small screw driver) back into the CCU when it is installed and check for ground to it (the tool), as the tool will contact the metal case of the CCU.

Hope somebody finds this useful and is spared trying to track down a ground point that doesn't exist.

-Ruben
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Old 05-06-2010, 03:41 AM
  #51  
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That's interesting information Archilla, and I agree on your conclusion on G18 being a ground output. That is probably done to obtain a common and good reference point for all sensors. There's an arrow on the 993 electric diagram, but not on the 964 version.
I see your findings regarding grounding of the CCU, but find it very unlikely that our german engineers rely on that risky kind of connection. That would rule out any HVAC function when having the CCU out of the dash opening.
Pin K1 (brown) is the main ground connection for the CCU, (going to ground point 3) so I also regard Brian's excellent DIY as somewhat unclear on this point.

It would be interesting to follow up on your measurements on G18, I'll have a look inside the CCU next time it's out of the car to see the output circuitry here.
Regards,
Tore
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Old 05-06-2010, 01:03 PM
  #52  
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"Pin K1 (brown) is the main ground connection for the CCU"

That's correct. And G18 is the sensor/actuator feedback ground which is
connected internally to K1 in the CCU.

A problem occurs if the harness fails (993 harness insulation recall) and power shorts to G18. This will in many cases destroy the CCU. Also, if the engine
has a poor main ground and one of the sensor grounds (G18) shorts to the
engine, this will also potentially destroy the CCU.

Bottom line: Pins K1 and G18 (@ the CCU) must indicate continuity (~ zero ohms) with the CCU unplugged.
Also, with the CCU unplugged, G18 should not indicate any continuity to chassis ground.
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Old 05-06-2010, 01:57 PM
  #53  
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Tore, Loren,

Great information. Thanks to you both for clarifying this. This makes complete sense, and now that I look more closely to the wiring diagram, I can figure out the grounding of K1. Deciphering the ground point locations on the wiring diagram is not that simple.

In any case, combining all of this information, the correct way to confirm the sensors are getting a solid ground would be to: a) confirm that K1 on the harness side has a strong ground, and b) confirm that K1 and G18 on the CCU side show continuity.

-Ruben
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Old 05-29-2010, 12:46 AM
  #54  
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Default Wow. I'm in awe!

Thank you Brian and all other contributors. I'm pretty new to the forum and have been hugely impressed that so many of you are willing to contribute the time in order to help guys like me. You know, semi-clueless.

Can any of you answer a simple question re: my wife's '95 993? I've traced her A/C problem to a partially frozen RH dash blower that keeps blowing the 25amp fuse. I've had success replacing the bushing/bearing in the engine compartment blower and am hopeful I can perform a similar feat for the dash unit....assuming I can get it out! I realize that there are a cople of torx screws behind the fan blades that must be removed. So assuming I get those out will the fan/motor come out and clear the firewall? Or do I have to remove the firewall first?
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Old 05-29-2010, 06:21 PM
  #55  
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For any of those interested, I answered my previous post. The RHS fan has been removed, lubed and reinstalled on my '95 993. A couple of notes to those needing to repeat my efforts.

1. I removed the firewall after the fuse box and heat sink were first removed. Slipped out pretty easily in fact. This provided the much needed room in front of the blower/fan. I don't think I could have done it with the firewall in place.

2. Removing the two torx screws has been discussed elsewhere on the forum. I took the advice of others and used a long skinny screwdriver to release the plastic tabs on the fan housing that lock the housing to the rest of the blower apparatus that stays with the car. Note! These two tabs are at 12:00 and 6:00

The fan spins freely after some engine oil was applied to the back bearing. If it craps out, next time I'll disassemble the motor and use a better lube. The cost of a replacement fan is now $740+/- so it seems worth the gamble.
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Old 07-02-2010, 08:24 PM
  #56  
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This thread delivers...

Cold air that is.

My a/c was "repaired" before I got the car, according to a receipt, it worked OK until this last insane heat spell. Thanks to this thread I traced it to a goofy resistor and an overcharged system, that manifold and gauge set paid for themselves in the first use.

This thread is a keeper. Thanks again to the members of Rennlist.
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Old 08-06-2010, 01:17 PM
  #57  
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Default Can you hold you engine @ exactly 2000 RPM?

Mis-post...Moved to new thread.

Last edited by TMc993; 08-06-2010 at 02:00 PM.
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Old 09-07-2010, 06:39 PM
  #58  
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Sorry to bring back a very old thread, but I just fixed a troubling AC issue.

Everything worked fine, until I would turn on the AC, it would blow for about 10sec, then stop, I would hear a HUMM/whooshing sound. Like the fan was stuck in a closed box.

Put on my Durametric scanner, it told me my fresh air servo was out. Replaced it, all worked well again.

This summer my AC started to do the same thing. Thought it was the servo again. Nope, servo worked fine, no codes stored.

I started to track down vacuum lines. Turns out there was no vacuum in the trunk @ the solenoid. From there I went back into the engine bay & started to test vacuum with a pump. one "T" would not hold vacuum. Then I started to see if all the lines were attached, NOPE! one was off, & I could not find out where it went. Pulled out the aux blower fan & started to feel around. I found the AC Vacuum line, it is on the drivers side running with the wireing harness, it goes to the bracket that holds the AUX fan, then goes under the intake plenum to the "T" (accually it's a 4 way T).

Turns out, there is a big black round canister attached to the intake plenum on the drivers side, right next to the 1 cylinder. On the back side of it, on the top there is a vacuum attachment. Mine was off. Attached it & ALL IS WELL!!!!!

I think mine fell off when I was doing my 90kmi service 2 years ago during the plug wire swap!!! Feeling a bit stupid & happy @ the same time.

here are some links that helped me....
http://privat.bluezone.no/toreb2000/ccurepair.html
http://porsche964.co.uk/technical/servos.htm
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Old 04-22-2012, 10:51 AM
  #59  
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Ever get stuck on the Philly Skucul ? The city built an in and outgoing road with two lanes and well, you sit forever; they event allow semi's and their manners suck. No AC on a unusual warm hot day. I checked everything and ended up trying to charge the ac. After about 10mins, and reving the engine over 2k, the compressor at last kicked ON ! I emptied one can of 134. After I turned off the engine and disconnected the charge hose, I tried the AC again and the compressor clutch refused to spin; although after reving the engine up the clutch at last spun. So now I have some AC for the Sckul.
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Old 09-26-2012, 06:00 PM
  #60  
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my fan on the ac only works in the max position, cannot get the fan to work on the heater or defroster.
can anyone help
thx
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