Jims928s4

My 87 S4 had the a/c converted to R134 by the PO.
I have found that one of the electric cooling fans don't work (r/h fan works ok but 2nd does not come even when a/c switch is activated) and front flaps did not appear to activate but they do stay open all the time.
While the a/c pumped out cold air it was'nt very cold. In the last week the cold air just became ambient temperature only.
I had it check out by my auto elec./air con. guy who regassed it and added a dye to check for leaks.
Results: a/c works intermittently on day one ie.
very cold air coming through.....check out again a few miutes later, system not activating......check again about 1.5 hours later a/c working again. Day 2...compressor not coming on system not activating BUT no gas leak, system fully charged. Interestingly I now notice that when cooling fan starts flaps open...when fan stops flaps close.
Sorry for being so long winded....
1) Would the R134 gas affect the actuation of the fans/flaps? (lower boiling point than R12)
2)What would cause the compessor not to start?
3)Would someone have an a/c wiring schematic for this model.
Thanks for any assistance.

lunchbox

Who charged up your system? Could it be overcharged? It takes a lot les r-134, than it does freon. If it is overcharged, the compressor will not come on. The low pressure switches like to stop working on those also. It is located next to the reciever/dyer. The flaps are vacume acctuated as soon as you hit the a/c button. Also if you have too much oil in the system it will cause weird happenings. That is good to have it evacuated by an a/c evacuation machine. Hope that helps...

Jims928s4

Thanks for that.However, the flaps I refer to are the ones located under the front bumper.

dr bob

[quote]Originally posted by Jims928s4:
<strong>My 87 S4 had the a/c converted to R134 by the PO.
I have found that one of the electric cooling fans don't work (r/h fan works ok but 2nd does not come even when a/c switch is activated) and front flaps did not appear to activate but they do stay open all the time.
While the a/c pumped out cold air it was'nt very cold. In the last week the cold air just became ambient temperature only.
I had it check out by my auto elec./air con. guy who regassed it and added a dye to check for leaks.
Results: a/c works intermittently on day one ie.
very cold air coming through.....check out again a few miutes later, system not activating......check again about 1.5 hours later a/c working again. Day 2...compressor not coming on system not activating BUT no gas leak, system fully charged. Interestingly I now notice that when cooling fan starts flaps open...when fan stops flaps close.
Sorry for being so long winded....
1) Would the R134 gas affect the actuation of the fans/flaps? (lower boiling point than R12)
2)What would cause the compessor not to start?
3)Would someone have an a/c wiring schematic for this model.
Thanks for any assistance.</strong><hr></blockquote>

1) The flaps and fans are actuated by engine coolant temp, and also by the freon hi-side pressure in the AC system. The sensor for this is on the little tubing manifold that's part of the receiver/drier assembly. On US LHD cars, this drier is located in front of the radiator on the right side (looking from the back of the car, right is right). It's a cylinder about 3" in diameter and maybey 8" tall. The pressure sensore for the fans and flaps is the one that has the little screw terminals with rubber caps over them.

As another responder points out, the R-134a has a different hi-side pressure, usually a little bit higher than the original R-12. The higher R-134a pressure will cause the fans and flaps to actuate a tiny bit sooner I guess; On my converted '89, they both go to full open/high speed immediately on AC start no matter which gas I had/have in there.

If you have one fan operating differently from the other, the problem is either in the fan controller module on the front apron, or you have a fan motor problem. Isolate the motor problem by swapping the two fans on the connectors; If the slow/erratic fan is the same with the plugs swapped, you have a fan problem. If the problem moves, go after the controller. The controller in this case is that black finned module up on the front apron by the hood latch. There is a tip somewhere about rebuilding this part, including some generic part numbers for the FET devices that seem to fail in there.

2) Three common posssibilities:

a) You are low on freon and the pressure safety switch is doing it's job.

b) You have a blown AC system fuse. Does the light in the AC button come on when the button is pushed and the engine is running? If so, the fuse is fine.

c) There's a little relay in the dash controller that is underspec'd for the duty, and they like to fail. I have a complete replacement procedure in a writeup that applies to your car. If your correct e-mail is attached to your Rennlist profile, you will soon have a copy of that in your inbox.

3) I have a CAD repredentation of the AC wiring for my '89, and might assume that the wiring for yours is the same. I don't have the manual set handy so I can't verify that for you. The diagram wil be sent also, along with the relay procedure.


As far as cold but not really COLD from the AC: I did this conversion a few years ago, and saw freezing temps (22f) from the center vent with the freeze protection switch not working. This is with 85f ambient, so the R-134a really will freeze you out of the car if you let it. Work with your tech, and appreciate that you will want to undercharge the system by about 10% for best/coldest performance. This is a steady but light stream of bubbles in the sight glass if you are charging by the 'visual' method.


Take a look at the diagrams and you'll get an appreciation for one of the more common problems, the relay. I was experiencing symptoms similar to yours, with erratic operation of the compressor. The relay fix did the trick for my car, and has also helped more than a few others keep their cool.

For those reading at home, the diagram and instruction are archived at the Nichols website and also on the Owners Club tips library.

Good luck, and Stay Cool!

WallyP

I seriously doubt that whether your system is R-134a or R-12 has anything to do with any of your problems.

dr. bob had a great deal of good info, but I would like to add one more bit. Your cooling fans have a separate fuse for each fan. Carefully check fuses 28 and 29.

Jims928s4

Doc
The info. you've provided has been fantastic.
I will check it all out and report back.
Wally,
I was aware of the dual fuses...both are OK.
Thanks for you're assistance in any case.

dr bob

[quote]Originally posted by WallyP:
<strong>I seriously doubt that whether your system is R-134a or R-12 has anything to do with any of your problems.

dr. bob had a great deal of good info, but I would like to add one more bit. Your cooling fans have a separate fuse for each fan. Carefully check fuses 28 and 29.</strong><hr></blockquote>


Thanks for the help, Wally.

I seldom think of fuses, since in my case, the
component usually fails first, protecting the fuse.


My name is Edsel Murphy, and I have a problem....

Jims928s4

Well.....Dr Bob has done it again!! The relay in the console was faulty as predicted, and the rectification procedure fixed the problem.
While it is stated endlessly, this forum is truely gold plated ( with the exception of some recent sniping) and truely keeps, and will keep these great cars on the road for ever.
Thanks to all who selflessly help novices like myself keep their cars running like they were originally designed.
(Now that my air con is OK....its back to fixing that fan problem!!)

PbFoot

Dr. Bob, regarding your Item (c) in the above post does that apply to 86½ 928S too (with only single fan)? Now that it is truly HOT here in FL I found that my car tends to run on the upper side of the temp gauge. When I turned on the AC, the electric fan does not come on. I bridged across the terminals and the fan comes on, so I know the motor works. Any idea where I should start? If it the the relay, please email the procedure as well. Much thanks in advance.

Greg86andahalf

I'll add one more FYI.

Usually, when converting to R134A, the original low pressure cut-off switch is replaced with one with a lower threshold. This prevents having the compressor cycle on and off, over and over again due to the lower low-side pressure of R134A.

Since I'm still R12, I don't know the absolute necessity of changing the low pressure cut-off switch on a 928, but it's standard practice on most R134A conversions. If I was to convert, I'd change the switch.

Greg

WallyP

The pre-S4 cars use a different fan switch on the A/C. The S4-up switch is a pressure switch, which triggers the fans as soon as the compressor comes on. The pre-S4 switch is a thremal switch, dependent upon the freon getting hot at the receiver/dryer. Doesn't work as well.

I still like the idea of fixing two things at once by adding a relay at the compressor. The small relay in the controller should last much longer triggering only the new relay coil. And, you could wire the fan to the relay so that it comes on with the compressor.

Shark_gts

The relay contacts are no doubt properly sized for the load. The problem is with a heavy inductive load like the clutch coil, there is a reverse voltage spike when the coil circuit is broken, causing an arc that degrades the contacts.

A simple diode from the A/C compressor lead to ground (current flow -ve to +ve) at the A/C compressor should prevent this.

Paul Jager

Shark_gts

I put a more detailed explanation on our site in the top ten tips page....

&lt;href="http://www.jageng.com/topten.htm"&gt;

WallyP

I still think that the tiny relay inside the A/C controller is too small for the load. I agree with Paul that the inductive kick is bad news.

If you check the wiring diagrams, you will find that Porsche has included a surpressor in the system. For the '85 & '86 models, for example, check Relay XI - it isn't a relay.

dr bob

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Shark_gts:
<strong>The relay contacts are no doubt properly sized for the load. The problem is with a heavy inductive load like the clutch coil, there is a reverse voltage spike when the coil circuit is broken, causing an arc that degrades the contacts.

A simple diode from the A/C compressor lead to ground (current flow -ve to +ve) at the A/C compressor should prevent this.

Paul Jager</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">The contacts in the relay are definitely NOT properly sized for the load, even assuming that there is no inductive kick when the contacts open. Clutch seems to draw about four amps across contacts rated for less, not withstanding the AC rating and the DC duty. Maybe we need a pre-fab DIY relay fix, prewired, that can plug in the spot on the board where the old relay sits. This makes it a reversible repair should you decide to go back to original later. Wally's idea about adding a relay under the hood is fine, but... I'm not a big fan of cutting into a perfectly good factory wiring harness to add a relay that's exposed to the underhood elements, etc. More than a casual amount of thought went into the published relay fix, especially the factors I stated.

Paul, do you want to package a "relay fix kit" or should I? <img border="0" title="" alt="[Wink]" src="wink.gif" />