A/C Troubleshooting on '82 SC

[francesconyc]

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

[wazzz]

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.

[Discseven]

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.

[francesconyc]

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?

[francesconyc]

Originally Posted by Discseven

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.

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

[francesconyc]

Originally Posted by wazzz

Do you hear anything when you turn the AC on (ignition on but engine not running)?

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??

[wazzz]

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.

[kuehl]

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

[francesconyc]

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..

[francesconyc]

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

[wazzz]

Originally Posted by francesconyc

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.

[kuehl]

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.

[francesconyc]

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

[francesconyc]

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

[kuehl]

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

[francesconyc]

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

[francesconyc]

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?

[francesconyc]

[wazzz]

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.

[francesconyc]

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...