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Discussion Starter · #1 ·
04 b5.5 Passat AWM Tip 1.8t

Thanks in advance. 馃檱 Been working on this car for months with many successful improvements. Now that鈥檚 it getting warmer it鈥檚 ac time. Here it goes. She鈥檚 a non climatronic.

Push ac button with the blower on; the indicator lights up and condenser fan runs. Engine running, compressor clutch does not engage. Put 12 volts to compressor, the clutch engages. When I first got this car I had the system evacuated in anticipation of having to replace the compressor.(I assumed, I鈥檓 an idiot) Now months later, trying to diagnose why originally the clutch wouldn鈥檛 engage. I鈥檝e pulled the 384 relay and opened it looking for solder joint issues with a jewelers loop. Looked great and it has 12 volts going to relay.

This is where we come to the issue. I鈥檓 wanting to jump the pressure sensor to rule out the 384, temp sensor, and pressure switch.(done with the ac drive belt off) Just trying to get the compressor clutch to engage. I realize the compressor could still be shot but not looking to buy anything not needed.

Back to jumpers on the 4 wire pressure sensor. Mine has red/white, blue/black, blue/brown, and brown. Ignition on with ac button pressed and blower going; R/W has 11.4v, blue/brown has 12v, and other two have 0. All pictures in write ups are no longer available. Trying to figure out what pins are 1&2 and 3&4. I鈥檝e read post saying to only jump the 1&2. Others saying both?

I have gauges, vac pump, and the knowledge to properly refill. But it won鈥檛 do squat if I can鈥檛 determine the original problem. I can get pictures as well as any other addition info needed to get this up and running. Additionally I have VCDS and the only climate code is low refrigerant pressure(from evacuation). Any help would be greatly appreciated. Thanks again.
 

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Unless I'm missing something here with your post, the a/c clutch WILL NOT engage when the system pressure is low. So if you've evacuated the system the compressor won't function.
As far as jumping the pressure switch to diagnose the a/c clutch, that can be done. Someone that's more electrical savvy than me can chime in about that.
 

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Discussion Starter · #3 ·
Thanks for the reply and yep you got it right. It will not engage when low. But when it was fully charged it did not function either, my brain went to replace compressor so then I had it evacuated. But yesterday I put 12v directly to the clutch and it engaged. So basically since I jumped the gun, my diagnostic agenda got much more complicated. But removing the pressure sensor from the equation would allow me to diagnose with the system vacuumed. I could attempt to fill it to the point the pressure switch activates. But if something else is wrong and I have to evacuate it once again to open the closed system I wouldn't be a happy camper.
 

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Have you checked fuse #25 (30A) ?

The switch should have the pin numbers marked near the pins.
My diagram shows different colour wires except the brown.
The brown wire is ground and connects to pin #4, the wire from pin 3 goes to pin 86 on the relay for high speed fan.
Bridging 3 & 4 would cause the condenser fan to run at high speed.
Bridging 1 & 2 should cause the clutch to engage. (The engine would need to be running)

NOTE: The clutch relay is not just a relay, it also contains electronic components.
 

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Thanks for the reply and yep you got it right. It will not engage when low. But when it was fully charged it did not function either
Hmm gotcha. That was the part I was missing.
 
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Discussion Starter · #6 ·
Holy moly, thank you. Go to bed, wake up with answers. I'll run a long wire from the 86 corresponding female and continuity check the other pins. Presto 1&2 and 3&4. Sorry this is so complicated, not trying to re-aim a headlight or remove the front plastics (did both in the last month) to get a peek at the pressure sensor pins. Thanks a million. I'll definitely report back, for future patrons.
 

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Discussion Starter · #7 · (Edited)
Edit: disregard this. This voltage has nothing to do with fan speed. Also the 3 pin appears to be 87a on the 384 relay.

Had a thought.
"R/W has 11.4v, blue/brown has 12v, and other two have 0"
Since the fan varies it's speed with voltage, would it make sense the 11.4v wire would go to pin 3? If so 11.4 volts seems like it's running at max speed or pretty close to it. What governs the voltage going to the fan? It's morning here and definitely cooler than when I checked voltage yesterday so I'll check it again and see if it's lower.
 

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Yeah at 12 volts (or there abouts) the fan should be running full speed.
The fan speed is controlled by the resistor mounted under the bottom side drivers frame tube horn.
Hood Vehicle Motor vehicle Automotive design Rim
 
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Discussion Starter · #9 ·
Thanks, hope it's not an issue with that. Could that inhibit the ac clutch from engaging?

So conditions after 1&2 jumper, ac belt removed, engine running, ac switch on, and blower on: AC compressor clutch locks up. Auxiliary fan running same speed/fast as before. Options..

A. Everything was fine when I bought it, but it was overcharged or undercharged. So the clutch wouldn't lock up.
B. The pressure switch has failed open on pins 1&2
C. Same as B but the fan speed side of pressure switch also failed, except it's failed closed causing fan to run at 12-ish volts.

Does this sound reasonable? All input is appreciated
 

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Edit: disregard this. This voltage has nothing to do with fan speed. Also the 3 pin appears to be 87a on the 384 relay.
384 is not just a relay, it is an A/C cut-off module with electronic components. It does not have a pin 87a. It could be easily damaged by incorrect connections.
None of the 3 fan control relays have a pin 87a.

Had a thought.
"R/W has 11.4v, blue/brown has 12v, and other two have 0"
Since the fan varies it's speed with voltage, would it make sense the 11.4v wire would go to pin 3? If so 11.4 volts seems like it's running at max speed or pretty close to it. What governs the voltage going to the fan? It's morning here and definitely cooler than when I checked voltage yesterday so I'll check it again and see if it's lower.
Voltage is not supplied to the fan from the A/C pressure switch, pins 3 & 4 provide ground to activate the high speed fan relay.
The low and high speed fan relays supply the correct voltage to the fan.
 

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Thanks, hope it's not an issue with that. Could that inhibit the ac clutch from engaging?

So conditions after 1&2 jumper, ac belt removed, engine running, ac switch on, and blower on: AC compressor clutch locks up. Auxiliary fan running same speed/fast as before. Options..

A. Everything was fine when I bought it, but it was overcharged or undercharged. So the clutch wouldn't lock up.
B. The pressure switch has failed open on pins 1&2
C. Same as B but the fan speed side of pressure switch also failed, except it's failed closed causing fan to run at 12-ish volts.

Does this sound reasonable? All input is appreciated
It looks like all of the a/c control systems are working correctly.

If the pressure switch pins 3 & 4 are failed closed, the fan would run at high speed as soon as the ignition was switched on, without anything else on.
Try bridging 3 & 4.
The only times the fan should run at high speed is when the refrigerant pressure is too high or there are extreme heating conditions.
 

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Discussion Starter · #12 ·
Thanks you. On the back side (male connectors) of the 384 rely there are numbers 87 and 87a just below the blades. Both connectors (female side) showed continuity to female receptor of pin 3. At any rate I was able to correctly identify 1&2 from 3&4 without removing plastics or a headlight. I jumped the 1-2 first, then 3-4. With 3-4 jumped, there was a noticeable fan speed increase. So pressure switch seems to be fine. I'm just going to flush the system, vacuum, and charge. At this point I can't find anything wrong. Hoping it was just under or over charged. Thanks agian
 

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Discussion Starter · #13 ·
So this is a wrap up post. AC still not functioning due to Washington state's bulls*** new laws. No pag oil, no refrigerant, and no flush for sale to the public.
Pulled a vac an the system and found no leaks. I had 1 can of r134a left from a previous job. Knew it wasn't enough to blow cold, but it was enough to satisfy the pressure switch requirements and further the diagnosis. So clutch locked up, dash switch functions, 384 works, and fans work. Gauge readings were (after 1 12oz r134a can added) high on low side and low on the high side. As well as bumping/fluttering needles. At this point it seems either there is a restriction somewhere or simply the compressor isn't functioning properly.
Giving I can't get the proper ac products in Washington, it's over. Might head to Idaho for a vacation sometime and buy everything I can get my hands on.
Thank you everyone for your input, I really appreciate it.
 
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