2000 VW Passat V6: Troubleshooting AC

xtvium · Jun 23, 2020

My 2000 VW Passat manual AC is not blowing cold air.

(1) I have checked the fuses on the side of the dashboard and no problem there.
(2) The fan is working at all speeds.
(3) The AC light on the dash comes on (amber).
(4) Manifold pressure measurements are as follows:

Cold engine, AC off - low pressure = high pressure = 40 psi
Warm/hot engine (~30 minutes of idling), max AC on, max fan on - low pressure 30 psi, high pressure = 100 psi (ambient temperature 85 F)
Warm/hot engine (~30 minutes of idling), AC off, max fan on - low pressure 73 psi, high pressure = 73 psi (ambient temperature 85 F)

(5) AC clutch - I cannot make out looking down from the front but wouldn't the manifold pressure reading change from AC on to off indicate that the clutch/compressor is engaging. Also, I see all belts/pulleys moving and do hear something clicking in the hood area few seconds after turning the AC on.

I think my pressures are on the low side for 85 F ambient temperature. But I woudl appreciate some experienced guidance to interpret above observations with certainty. TIA>

Tomvw · Jun 23, 2020

It appears that all of the electrics are working properly.
Without the right knowledge and equipment, you are not going to get the right amount of gas and oil.
I suggest you take it to an auto A/C mechanic, and get it vacced out, and get it filled with
the correct amount of oil and refrigerant.

xtvium · Jun 23, 2020

Thank you @Tomvw... so you too think it is the low charge that is culprit. I agree with you the recharging and possibly leak detection/fixing is best done by a shop since I don't have a way to recycle the refrigerant even if I can vac it out. And then there is the issue of the oil. I carefully inspected the lines and I don't see any oily residue on them anywhere. Wonder where the refrigerant went.

Is this something a shop like Meinke, Firestone, etc., can be trusted to do well? I have both less than mile from home.

VAGguy · Jun 24, 2020

Meineke, hell no. Firestone, maybe. What has your personal experience been with either shop?

Also, it's a 20yr old car. Seals can harden and leak over time. The tell-tale is an oily residue. If it is a leak, they will find it when they draw down the system doing the evac. If you need any o-rings or receiver/drier or orifice tube (all should be done when cracking the system open), let me know.

Hirnbeiss · Jun 24, 2020

Your pressures are definitely low, and if the readings are right the compressor is doing something. I would add a can first to see if you can get high-side to where it should be (at least 250 psi). Let us know the results.

xtvium · Jun 24, 2020

VAGguy said:
Meineke, hell no. Firestone, maybe. What has your personal experience been with either shop?

Also, it's a 20yr old car. Seals can harden and leak over time. The tell-tale is an oily residue. If it is a leak, they will find it when they draw down the system doing the evac. If you need any o-rings or receiver/drier or orifice tube (all should be done when cracking the system open), let me know.

I have no experience with Meinke, so I will heed your advice. Was once at Firestone for some tire-related stuff and it was OK, but I don't know how that translates to what I can expect for the AC service there. AAA Autocare also nearby. I guess this is a simple enough job that I don't need to go to an indy specializing in VWs/European cars.

Tomvw · Jun 24, 2020

No you don't need an indy specializing in VWs/European cars.
You just need someone who knows Auto A/Cs.

xtvium · Jun 24, 2020

Hirnbeiss said:
Your pressures are definitely low, and if the readings are right the compressor is doing something. I would add a can first to see if you can get high-side to where it should be (at least 250 psi). Let us know the results.

I really am tempted to try dumping a can (or part of) to see if I can get cooling going. However, two things give me a pause - (1) there is obviously a leak and it is probably better to fix it (2) the oil loss - I can replenish the R134a but have no way of making sure the refrigerant to oil ratio is correct. or am I overthinking this...

FrescoGreen01.5 · Jun 24, 2020

I think your reasons for pause are appropriate. If you want to do anything more than limp along a few months or dump the car, get the A/C serviced professionally.
I would call and ask each garage if they do A/C service in-house and how many licensed A/C techs they have. Unlike a lot of jobs on these cars, the parts are not outlandishly expensive and it doesn't require a VW specialist, so why risk making things worse?
I would call Firestone and AAA Complete Auto. And if they don't do A/C service work, they'll probably tell you who does.

AndreasPassat · Jun 24, 2020

Agreed with FrescoGreen's post.
You don't need a VW/Audi specialist. Just a reputable a/c shop.
To have a shop do a complete evacuate, test, add PAG oil (with dye) and R134 should run you a max of $150.
During the testing phase they'll tell you were the leak is if any.
If parts are needed, they are relatively inexpensive. The compressor is the most expensive component. But the chances of you needing a compressor are slim.

Tomvw · Jun 24, 2020

If you are paying to have the part/s fitted, I think you would find that an evaporator
would be more expensive than a compressor.

VAGguy · Jun 24, 2020

Tomvw said:
If you are paying to have the part/s fitted, I think you would find that an evaporator
would be more expensive than a compressor.

Yep, the labor alone will tip the scales in that direction.

AndreasPassat · Jun 24, 2020

Tomvw said:
If you are paying to have the part/s fitted, I think you would find that an evaporator
would be more expensive than a compressor.

VAGguy said:
Yep, the labor alone will tip the scales in that direction.

100% agreed.
I probably should have mentioned it. My statement of the parts being relatively inexpensive, would be if you did your own wrenching and purchased from your favorite online parts supply.

2000 VW Passat V6: Troubleshooting AC

xtvium

Tomvw

xtvium

VAGguy

Hirnbeiss

xtvium

Tomvw

xtvium

FrescoGreen01.5

AndreasPassat

Tomvw

VAGguy

AndreasPassat

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