A/C Troubleshooting on '82 SC

[francesconyc]

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!

[wazzz]

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).

[francesconyc]

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?

[wazzz]

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.

[francesconyc]

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

[francesconyc]

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

[francesconyc]

[wazzz]

Originally Posted by francesconyc

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.

[francesconyc]

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

[francesconyc]

Originally Posted by wazzz

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.

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...

[francesconyc]

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?

[wazzz]

Originally Posted by francesconyc

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.

[francesconyc]

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?

[francesconyc]

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?

[wazzz]

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.

[francesconyc]

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?

[francesconyc]

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

[wazzz]

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.

[francesconyc]

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

[francesconyc]

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