A/C Troubleshooting on '82 SC
 

My AC doesn't work but I finally decided to troubleshoot it and give another change after I discovered a PO receipt for some upgrade they did in the recent past.
Like many SC other oddities, I bet AC also has some and it makes it difficult to test things unless someone helps you...

so, here are some facts:

What I know

• I was told by the PO there is no freon, so I need to recharge it
• I know PO replaced all the AC lines going from the compressor to the evaporator (smuggler box)
• I saw there is a Kuehl dryer on the driver's wheel area
• I was also told that the system was working
• The compressor in the back works. it's the old stock model.

What I tried so far

• I used a multimeter to see if there is DC on the evaporator wires, but I'm not sure if I tested the right ones. in both cases the value was 0, with the ignition on, the AC knob in the console turned on to III (3)
• I replaced all the fuses in the trunk and in the back with brand-new ones

FYI I have the Bentley but not super clear to understand

Where would you start? my guess is to check if there is air (not cold) blowing through the center vent right?

some images:
https://imgur.com/zwHpK9g
https://imgur.com/HBtqy91
https://imgur.com/dDfK6m0

https://imgur.com/zwHpK9g
https://imgur.com/HBtqy91
https://imgur.com/dDfK6m0

As a safety measure I would first disconnect the compressor clutch wire, since you said the circuit is empty (no freon). Otherwise damage can result if you try to make the AC components work while the engine is running.
Rest of it is just tracing with the help of proper diagram. Do you hear anything when you turn the AC on (ignition on but engine not running)?
Go through the wiring diagram or current flow diagram for your car and check with your multimeter where the power (+12V) is and where the ground (0V) is when you turn both switches fully to the right. One is the thermostat switch and the other one is the 4-position switch that controls the evaporator blower. If you want to test power for this blower you need to set this switch on position 4 (full blast), which is the only position where you will see 12V, if present. Other positions run through one or two resistors that will make the voltage reading lower. Of course voltage is to be measured on the source side, not on the load (motor) side.

http://forums.pelicanparts.com/uploa...1711277506.jpg

If the system was working (and by this we shall assume it to mean cooling adequately as opposed to the compressor just running) and THEN and now there is no refrigerant in it, that info suggests the presence of a leak. I would start with this because if there is a leak, no matter what else is done to the system, it may run/cool for a while but will progressively fail.

To check for the presence of a leak is relatively a simple matter provided you have a vacuum pump. (Vacuum the system out and see what happens... a vacuum will hold if the system is sealed. It will fail if there is a leak.) If there is a leak, that is the starting place.

thanks. I guess I will start literally from the switches in the cabin console then. I'll check first off if 12DC power goes from the battery to the switches... THEN if all is good, I'll check again if the power goes to the evaporator motor correct?

I don't think there is a leak. the PO simply stated he never used the AC in more than 7 years so I guess new refrigerants like R14 tends to leak no matter what.

either way my problem is not the leaks now. is the motor that doesn't switch on

no, I don't hear anything.

In the past, I think, I heard some buzzing noise coming from the smuggler box, then I removed the AC fuse just in case

then yesterday I spent more time on it, put back the use, and when the key is on position 1 (battery on)
nothing happens if I turn those knobs to max.

btw how I disconnect the clutch on the compressor??

Electromagnetic compressor clutch can be cut off by simply disconnecting the black wire and green wire at connector T1a on diagram. Just follow the only black wire visible on the compressor and you should find this connector.

1) PO said there was no refrigerant? Well, for the moment accept it as a fact.
No sense trying to run the system if you know there is no refrigerant in it.
Its the refrigerant that moves the refrigerant oil through the system and that is how the internal moving parts of the compressor get lubricated... by moving refrigerant.
No refrigerant oil, or no refrigerant and the compressor wears and starts tossing its cookies through the system and the becomes a very expensive "oh I did not know that" problem some personally experienced.

2) If you want to check if the compressor is getting electrical power to engage the clutch:
A) Car parked on flat ground. E brake on. Trans in neutral in case you turn the key too far. Turn ign key to the 'on-accessory' position (that is just before you would feel resistance in the next position that cranks the starter), so 'on accessory'.
B) RH knob in the center console is Evap Fan Mtr. Turn it CW (to right) to any of its 3 clicks, speed 1,2, or 3 for a stock fan speed control. If you feel or hear the evap fan motor running, that's a bonus.
C) LH knob in center console is AC Thermostat. Turn if fully CW. If you hear another fan motor turn on in the front trunk area that's the front condenser blower motor running, that's a bonus.
D) Pull your engine lid lock release lever and go back to the RH rear corner of the engine bay with power check light or VOM. Locate the wire coming from the compressor leading to the area between the oil filter and the RH tail light. It should connect to another wire with 'spade' connector. Unplug the connection and check for power coming out of the male spade terminal (this terminal is power feed coming from the thermostat); red test lead on male connector and black test lead to compressor body or vehicle body ground (powder coating your compressor brackets is not a good idea for grounding). If you have fully charged battery, most do not, the voltage can be less than battery voltage (voltage drop do to the long wire run). If you have power at the male spade you can 'assume' your AC circuit is working. If not then you can get into the schematic and work it back all the way to fuse #2 (blue 25 amp closest to the windshield in main fuse/relay panel in the front).


3) Turn off the ign key and turn both AC control knobs fully CCW (to left). You noted the PO changed all the hoses but you only listed one; evap to compressor. On
a stock system there 5 hoses. Go back to the engine bay and locate the hose from the compressor to the deck lid condenser (RH hinge). Is it new? Is its simply a hose with a fitting at each end or is there a 'pressure switch' with 2 wires attached to in on the hose? Something to discuss later.

4) If you have AC gauges and know how to use them you can check to see what the pressure is in the system without the AC running; knowing that pressure and looking up what it is compared to the ambient temperature around the car outside can give you a very good idea as to how much of a refrigerant charge is in the system. If you don't have gauges or never used them you can ask a fellow Porsche owner to help you or ask a repair shop to do a quick test; some do it for free (toss them a $20). Let the forum know what you find out. You could do a quick 'psssssssstttt' test to check if there is some refrigerant in the system by pressing in a Schrader valve but technically that is illegal and not an empirical method.

5) Pulling a vacuum, with the best pump in the world, at sea level, is only equal to 1 atmosphere of pressure or 14.69 psi. You can have a system that does not leak 14.69 psi but does leak at higher pressures which expand a crack in a hose or expand an o-ring.


Power to clutch

http://forums.pelicanparts.com/uploa...1711290658.jpg

wow, amazing help.

I guess for now I'm stuck at your point 2.B
following the procedure with key on
I cant hear anything going on in the smuggler box
I haven't checked the front fan but I would have felt some sort of noise if it was working...

also, tbh I need to check if every single relay above the fuses work... for full diligence..

to clarify:

if with key on 1, battery on
if I turn the RH to III, should I get air from the central vent or not? I'm still stuck on this question

Yes you should.

If your AC evap motor switch and the Evap Fan Resistor Unit are both working properly, you will get air from the vent above the radio, at any speed.

Based on common failures in this situation, 42 years worth for your car, the common modes of failure are (in no order):
1) #2 25 amp fuse
2) primary AC relay adjacent to the evap box in the smugglers box well in the front trunk
3) evap fan speed switch
4) evap motor

You can simply test the evap motor to start. Unplug the molex connector at the motor. Provide 12dvc to the male spade red wire, and ground to the brown wire. You can run leads from your battery or carefully use a battery charger. If you feel flaky about testing it this way you can put a 20 amp fuse inline of the positive you run to the motor.

If the motor tests good then you can jump back to the #2 fuse and work your way forward.

Btw do you know what is this whirring noise coming from the smuggler box? I disconnected the from ac fan and the evaporator fan, disconnected cluth con compressor but i can still hear it

Here the video of the noise
https://youtube.com/shorts/V7thpVse9pw?feature=shared

there is the fuel pump below on the cross member, but they usually are not that loud!
pull FP relay or fuse

Ooh i see makes sense

Is louder in the video than in reality as i noticed only when inspecting the AC

Good to know!
Thanks

On i finally had time today to start troubleshooting the wires of my AC switches
I tested the right switch (0123) and i dont get any readings of dc voltage here. I tried both with engine on/ and just ignition on. Only few millivolts to be exact.

The green wires seem correctly connected to the ground. The red wires who knows. I know for sure it was working at some point for the PO so i dont see why the wiring to the switch can be cut in some places?

The fuses are all new, same for relays.

What can be wrong or am i doing the procedure correctly?

Check the wiring diagram I posted above, with the current path added later in red by Charlie.

This switch only receive power (+12V) if the relay further down (called Relay AC) is good and energized. Check this point first. If you read any voltage at the switch, the power source upstream is not functional. Follow the current flow on the diagram.

The relay for AC in the trunk is good and tested.

so, should the 12v reading be at the switch/wires when engine on or is sufficient ignition on?
i tried both but nothing...

Ok lets do some baby steps. I found onBentley a diagram that is a bit more clear.
And tell me if this procedure makes sense:

1. Check if fuse 20 is hot (12v)
2. Check if AC relay works
3. Start the engine
4. Check AC control switch: connect multimeter to FULL RED wire and the Green/white wire (ground) to check if they are hot (12v)

Does it make sense? I literally just want to know only if the power arrives to the switch then we will cross the bridge weather the switch needs replaced or not

Thanks!http://forums.pelicanparts.com/uploa...1712539918.jpg

To answer your first question a couple of posts ago: "should the 12v reading be at the switch/wires when engine on or is sufficient ignition on?". Yes, ignition on is sufficient, this is what the "Hot in run or start" means on your last diagram.
What Bentley calls Run position is when you turn the key to ignition, and Start position is when you crank. These powers are called 15 in automotive. Permanent hots (battery positive, or "Hot at all times" as it appears on your diagram) are called 30. You will find this on all diagrams, whether factory or Bentley.
So, you are saying that the AC relay is good but don't tell us how you tested it. When ignition is on, no matter if engine is running or not, you should have power (12V) on terminal 85 of this relay, that is the black wire coming from the "Hot in run or start". In this situation, relay's internal switch closes and provides power to the plain red wire. So you should find power on the plain red you circled on AC switch.
Then this power should be found also on the green/white when you turn AC on position 1, 2 or 3.
You should also find power on red/green when AC is turned on 1, red/black when AC is turned on 2, and red/white when AC is turned on 3 (full blast).
Just follow the diagram, whether the factory diagram or Bentley diagram.

If you don't find any power on AC switch, not even on plain red, then the issue lies upstream at the relay. You need to check if you have a ground at relay terminal 86, the other leg of the coil. This is the yellow wire. But beware, this wire becomes hot (12V) when cranking the engine.

Also, when checking power presence, make sure you do it with a known good ground as a reference, meaning you apply red probe at the point to be tested for power (+12V) and the black probe at a ground point nearby (group of brown wires connected to body).

Thanks very clear now! Im learning lot of terminology thanks!


The way I tested my relay is simply switching them to the horn relay position then, bump the horn on the steering wheel. I did for all 5 black relays. Engine off, ignition off.

Does it make sense or something else may hide in those relays?

So you know your relay is good, but that doesn't say that the socket where it plugs is good too. Problem may lie there. Test voltage at the relay socket terminals and see if power is present at terminal 85 (coil) and 30 (power source from fuse box) when ignition is on. This can be more easily done with the relay removed. This way you can probe the relay socket female terminals with your multimeter. Again do these tests with reference to a known good ground.

Oh very interesting, havent thought about that!
Thanks again for these super useful suggestions!

i finally tested today the socket for the AC relay, the relay itself, and fuse again for the AC and everything seems ok.
I tested again the switch in the cabin, and between green/white cable and the red cable i have only 7millivolts (strangely not zero though...)

it seems is literally missing the power going to the switch from the battery/fusebox...

is there any other fuse or whatnot between the switch and the battery?
i guess i need to locate the entire wire... and see if by any chance it was cut/ got loose at some point...

this part is something i have no idea where to look for... do all these wires pass through a firewall?where?

thanks again for helping me

Sorry but your description is not very clear. There seem to be some confusion about what you are testing and how. From what you describe I understand you tested voltage between red and green/white at the AC switch, but you don't mention on what position the switch was when you did that test. Assuming the switch is on position 1 through 3 and not 0, what you are actually measuring is power (+12V) against power (+12V) instead of power against ground. No wonder why you get near zero voltage (7 millivolts). Check the diagram. When this switch is engaged on one of the rotary positions, red and green/white are in contact, ie. they are at the same potential. Therefore no voltage between them.

I suggest you disconnect car battery and switch to continuity testing with an ohmmeter. Testing voltages in various points is only valid if you know what to expect. Continuity/ohm testing is safer and less prone to meaningless results.

I tested the ac switch in all position. But in theory the most important is just the green and red (just red) wire which measure the voltage coming IN correct?


If I had voltage coming IN and not out I would know the problem is the switch but in my case it seems zero in any position. Im gonna try again.


Btw im testing both with ignition on / engine on.

The PO must have done something because some parts are relatively new (3-5yrs old) so i bet it was working.

I wonder if there is a loose connection between vattery and switch at this point.
Also i just bought a spare battey 12v 7a to test separetly all the fans in the trunk

Will report back

oh wait a second... are you saying that the green/white is not ground??
I thought the full red was giving power to the other "red-striped" wires...

where is the round then? ugh I'll test tonight again then...

i check ohm between the green/white wire and a random nut on the seat, or body.. and they seem connected (0.00 ohm) so I thought green = ground...

update: i tested again the AC switch inside the cabin and this time I connected the multimeter's black wire to the car body, then tested each wire of the switch. No 12v at all. tried all 0-3 positions. nothing. maybe I'm doing something wrong.

Anyways. in the meantime. I was wondering, can I at last test the evaporator fan (inside the smuggler box) by connecting a battery (I have a battery 12V 7.2A) directly to the switch (RED/WHT wire of pos 3) instead of in the trunk? should I remove any fuse first ?

if it works I can test the other red wires (pos 2 and 1) which would at least tell me that the fan and the resistors work.
thoughts?

No 12V? Not even on the plain red wire (terminal C) when ignition is On? Then you are back to following the path between AC relay terminal 87 and AC switch terminal C. Check the diagram.
In short, you are saying that power (12V) is present at the AC relay output (terminal 87) but not downstream at the AC switch input (terminal C). Please confirm.

Now if you want to test the fan motor I would suggest you do it right at the motor connector by disconnecting it from the car and plugging it to your external power source. No matter what polarity, motor should run in both directions.
Don't connect the external power source at the AC switch or you are going for trouble. Or at least disconnect car battery and remove fuses. But this is more complicated and will not help. Test the blower with an external battery.

correct.

I have no 12v at the switch in any of the wires reds&green in any 0-3 position
but if I understood correctly the most important is the plain red wire that is the one that brings the power into the cabin console switch.

also If I understood correctly the power goes from
battery to > relay to > fuse to > AC switch right?

In my smuggler box, I have two cables, left and right of the black housing fan. I have no idea which is which, also I don't know if I have to test the female or male plugs

I will disconnect the battery and also test from inside the cabin/switch, so at least I can confirm that the wiring from the switch to the fan (if the fan works) is also good.

is a motorcycle batter 12v 7a enough for a short test? is guess so right?

Update: the AC center fan is working.
How I tested: disconnected the clutch in the back, removed ac relay and inside the cabin, the AC switch, i connected a battery to the red/white wire (corresponding to pos 3) and the fan worked!!!
I tested the other red/blk and red/grn wires and the both worked: which should tell me that also the resistors at the passenger feet work.

At this point i bet the other fan and the clutch will work when connected.

It seems the culprit is the wiring between the fusebox and the switch inside the cabin.

Now, tomorrow I’m gonna remove the center console again to see if by mistake the previos owner made any mess with the wire.

I was wondering that in the worse scenario i can simply commect a new wire and pass it via a firewall hole no?

Any other recommendations/thoughts?

I cannot understand why you still haven't checked continuity between terminal 87 of AC relay and terminal C of AC switch. Told you to do this test. Simple.
Use an ohmmeter and nothing else. Disconnect the battery first.
You may need to extend one of the multimeter probes with a length of wire to reach both points to be tested. Please simply do that test and report.

Tested today. Confirmed there is no continuity whatsoever between the plain red cable inside the center console in cabin and the fusebox or relay (tested all 5 holes) with inigiotn off (and on just for diligence)

there is continuity between the relay and the fuse. The fuse is brand new. The relay works.

now essentially we are down to understand where the wire is loose or has been cut by mistake

does it pass via the passenger's feet by any chance?

After inspecting the wires, the plain RED wire goes along with a bundle of other wires that go through the firewall to the trunk are, I have no idea what's their route specifically.

but assuming is impossible that someone cut the wire in the past, I can only think the problem is between the plain RED wire (C) and the relay (87)...

Should I remove the entire fuse box? how do I inspect it? maybe the wire behind the relay is loose? it's literally the only thing I can think of

Check the factory official diagram I posted on previous page, there's a connector point (ref. T4b) in between along the way. The plain red is not one continuous wire. Check this for continuity. Disconnect battery first.
The factory diagram is more accurate than the Bentley, which is more like a simplified current flow diagram.
Also if you suspect something wrong with the relay socket, you can pop it out, as it is only held by the rubber lip, and see if it is correctly wired.

oh I now see the T4B connector... maybe that's the culprit! will check both that and the relay socket asap...

any clue where I can find that terminal in the jungle of parts between the fuse panel and the cabin?