Need some help troubleshooting my A/C
 

Going through my A/C on a 78 911 SC - Euro. It may not be a factory install because the "front" condensor is in the back behind the driver side rear wheel.

I am trying to figure out if the compressor clutch is functional.

Here is what I have right now.

System not run since I got it in 2009. Have not hooked up the A/C belt since motor installation. I checked for pressure by pushing in on one of the fill fittings and it still has pressure (so maybe just needs a recharge).

According to the schematic from the bentley (dwg 970-12):
Ignition in run should pick up the A/C relay (have not found it yet - not in the fuse box as it should be - another indication that it was not a factory install).

Turn the A/C fan switch to postions 1, 2, or 3 - Evaporator fan blows with increasing speed. This tells me that A/C relay (where ever it is) is working.

That should put power to the A/C switch which should pick up the clutch - got nothing.

Either switch or clutch is suspect at this point.

Placed twelve volts onto the wire leading to the compressor (down stream of the temperature switch - heard a relay pick up and then the condensor fan started. Did not hear anything at the compressor; spun the pulley and it moved freely. This gives me an indication that the A/C temperature switch may not be functioning, but I am not sure if it tells me the compressor clutch is not functioning.

Did some resistance checks and found the following:
from the power line to compressor case - 3.4 ohms - looked reasonable for a coil.
Compressor case to ground - 90 ohms - Shouldn't the case be a solid ground? Thought I would ask before I make it a solid ground and then fry something in the process!

Thoughts?

Sounds like you have the same system on your ROW '78 that I have on mine! I just bought the car and was looking all over for the condensor and found it back there where yours is.
Haven't figured out the wiring for the AC yet, or even if it works.
Getting ready to drop the engine and fix the oil leaks next.

I'll be watching this thread for info for future reference though, we can't have the only 2 '78 ROW cars set up like this on this forum...LOL

Although you have pressure at the service port, you may not have enough pressure to trip the low pressure cut out switch, which is usually located on the reeceiver drier. On my '79 the receiver drier is located behind the front drivers side wheel. I would jump this switch with the engine not running and see if the clutch engages. If it does, then you will need to add more refrigerant to the system. In order to get the low pressure switch to close.

Id check with Griffith's as they are the ones who make the condensor setup by the rear wheel.

Thanks for the replies
 

Timmy2 - always comfort in numbers - glad to know I am not unique in my setup. I have heard that the Bentley manual is good but does not accurately reflect all setups, so maybe this is simply one of those cases. or maybe we both have the same aftermarket install. either way, good to not be completely unique!

Crow - was not aware of the pressure switch on the receiver - I will try to locate and see if I can do as you suggest. However, the schematic does not show such a switch (does not mean it does not exist) and when I applied power directly to the wire at the compressor would it not have done the same thing as bypassing the switch? The griffith's site RSTarga recommended did address that a pressure switch exists so this is something that I will need to look into as I am not currently getting twelve volts to the compressor without using an external voltage source. So, even if I fix the ground connection, it still may not work until I get some more pressure in the system.

RSTarga - your recommendation to go to Griffith's gave me both some good basic information which I could use and some troubleshooting guidance. They indicated a good coil was between 2.9 and 3.2 I am getting 3.4. They also indicated I should have a good ground on the compressor case and I currently have 90 ohms which would definitely reduce the current below the necessary 5 amps needed to pull the clutch in. I will pursue improving the ground connection on the compressor and go from there.

ThanksSmileWavy

Do you know what kind of refrigerant you are dealing with? If it is R134, and you have pressure, you might try adding a can to the system or just having a shop "service" it. If it is R12 a bit more complicated. Picture of the compressor with the line in/out and service ports helpful.

It is almost the end of the season. I would drop a ton of $$ into it right now. A can of 134 at NAPA won't cost you much and often times comes with a gauge. The engine fan pulls air through the rear condenser on the engine lid (if you have that) so it has to be closed as much as possible to keep the high pressure side "reasonable". You have two dials on the AC panel. One has to be turned all the way clockwise and the other is the fan which has 3 speeds.

You can check at the compressor for 12v at the plug which is either on the compressor or at the end of the wire that comes off the compressor.

Hope this helps some.

So I took a better look at my A/C system tonight and it appears to be some kind of hybrid, probably constructed when the car was imported as described in some A/C articles here on the site.
It has a Seiko compressor R-12 model # SS-170PSV, with a BEHR unit in the smugglers box, and a fan in the engine compartment ducting air into the drivers wheelwell to an evaporator that is shrouded behind the wheel. The controls are mounted to the dash between the steering wheel and the ashtray as I have no console. They consist of a single dual rotary switch with 3 speeds on the inside and a spinning dial on the outside with 2 stops 370 deg apart. The Drier is in the Driver's front wheel well and has a sight glass on top, it has porsch numbers on the mounting straps but no other visible info.

current status
 

Pretty sure I am dealing with an R12 configuration.

I put power across the input line and the compressor casing - Clutch engaged.

Now I have two challanges yet to solve:

1. How to get a solid ground to the compressor. There are three mounting bolts - 2 are on the mounting plate and appear to have insulator/shock mounting systems which would inhibit a good ground. The third is on the adjustable arm used to tension the belt - it also has a insulator/shock mounting system. So, if those are the three contact locations, I would figure that one of them needs to be assembled such that there is a good ground connection using washers designed for continuity purposes. Either that or I am missing a wire or a concept some where. Here is a picture of the compressor.

http://forums.pelicanparts.com/uploa...1314676581.jpg

2. Continue to trouble shoot the voltage path through the temperature switch because even if the clutch will work, I have to succesfully get power to the clutch via the normal circuit. Off to pursue this path as I ponder the ground issue.

Sounds identical
 

Timmy2 - your description with the exception of the console is identical to mine.

What I am challenged by is the wiring, I only have 18 fuses so I know it's not connected as the factory units are to Fuse 20 so it's a game of trace and chase...
I have a power relay mounted below the fuse box that feeds the unit and controls. Just need to figure out the relay in the engine compartment to build my own schematic.
I'd have you drop by so I can look at yours with you, but it's a 4 1/2 hr drive down the gorge!
Nice scenery but A\C sure would be nice at the "hot" end where you live...
:)

ditto on the wiring challange. As I progress through this I will take some photos and make some drawings for myself. Will get you some as I go. I know the condensor relay is in the back because I can here it pick up when I power up the compressor clutch - just haven't searched for it yet. The main A/C relay and fuse I have not figured out at all yet, just know that it must be working because the evaporator fan runs.

Looks like your service ports are R-12

Any thoughts on how the compressor is grounded?

Timmy2,

OK, learned a few more things about our set up.

First, the relay and fuse for it in my set up is in the engine compartment. Here is a picture of it:

http://forums.pelicanparts.com/uploa...1314763264.jpg

The relay is a square relay in my set up with an in-line fuse holder providing the power.

I went to try to short out the wire at the drier to see if I had an operational system and looked behind the drivers side front wheel and found nothing. Then I recalled that there was something installed above the thermal valve for the oil system and sure enough, it was the drier - back in the passenger side rear wheel well.

So, as it turns out, the system has some pressure, but not enough to trip the switch at the drier.

So, once I get a solid ground on the compressor, I think I will wait to spring and have the system evacuated and filled and go from there. That will give me the winter to ponder putting in the newer hoses and potentially go to the R-134 set up.

Case is probably grounded through the bolts to the motor. If you really want a solid ground you need a wire from a bolt to the engine block or even the car's chassis. I am an electrician so I just happen to have a supply of the braided flat wire the rest of the engine to body grounds are made of. I will make one up tomorrow for mine and take a picture, If you want one I'll make one for you, just tell me the length you want if you like mine. Should look real nice.;)

Timmy2 - sounds like a plan. I came to the conclusion last night that it probably does need an external ground and seeing how all three of my mounting bolts are vibration/insulated I would have to ensure that one of the bolts was making good contact or use an external wire. A braided strap sounds like just the ticket.

Life got in the way today, didn't get a chance to make anything. Also need to get the right connectors that will work well for this application. Guess I used them all up on previous projects...
I'm going to get a couple made up by the end of this weekend.

Ok, Life was better today and I made up a strap for you.
I thought you could mount it to a bolt holding the compressor on one end and attach the other end to the stud holding the fuel runner below it right where the ac bracket bolts up.
PM me with a mailing address and I'll throw it in the mail this weekend if you want it.
Here is a picture of it sitting on my mirror so you can get an idea of the size.
I used the braid to match factory style spark plug wires.


http://forums.pelicanparts.com/uploa...1314930299.jpg

Put it in a mailer and addressed to you. My wife will mail tomorrow.
The ends are soldered, not crimped, so it will last.
Interesting thing is the stuff I used appears to be identical to the cover for the spark plug wires! I threw a small piece in for you to look at.
I might just buy a less expensive wire set and cover them myself when I replace my wires.

I looked at my AC wiring again and my relay is different. It is steel and mounted to the firewall
behind the black cold start relay, next to the 2 stage heated rear window relay, on the left in the picture. (You can't see it from this pictures angle)

http://forums.pelicanparts.com/uploa...1314935382.jpg

mycastle.
Let me know if the ground strap is helping, I know it's 100 degrees where you live right now!:eek:

So I looked under my car today before I put it on my new (used) scissor lift and I couldn't believe what I saw. There is a condenser that is ****** huge mounted to the bottom of the front floor. :D
It measures 14 by 40 inches! :eek:
If my system is fully charged this car is gonna be a fridge!
Here I was thinking that all I had was a condenser in the rear wheelwell and the air would be crappy. This Monster must have been installed when the car was in Arizona!
Have to wait until I'm done my engine drop for leaks before I know for sure if it works.
I'll post a picture later.