Automotive Air Conditioning Information Forum (Archives)

stuvx on Sat August 11, 2012 9:28 PM

Year: 2007
Make: VW
Model: Passat
Engine Size: 2.0T
Refrigerant Type: 134ac
Ambient Temp: 88 F
Pressure Low: 45 psi
Pressure High: 240 psi
Country of Origin: United States

Help.

I have a VW Passat that doesn't cool very well despite gauge readings that look normal and a correct charge of refrigerant. I can only get center vent temps down to 60 deg F, should be closer to 40-50 deg F. Originally, car had a seized compressor so I replaced the compressor, expansion valve and condensor (came with new receiver/drier built in to new condensor) with all new components. I flushed evaporator and lines before I vacuumed and refilled with 600 grams
of R134a.

I also have a vagcom that shows the a/c computer is sending approx 1 amp to the compressor control valve and verified current readings at the control valve connector with a multimeter. Repair manual says 1 amp should produce roughly 25 psi on the low side but I'm only getting 40-45 psi.

So I believe the compressor is getting the full current to maximize stroke and I have the correct amount of refrigerant but it's still not getting cold enough (60 deg F center vent temp).

What could I have done wrong? I' ve even tried a new compressor with the same results.

Thanks for any help.

[Update]

I blew out all the lines, condensor, evaporator, and drained the compressor and that seemed to fix the problem wih poor cooling and high low side pressure. Now I'm getting 30 psi low side pressure and about 45 deg F out the vents at about 1500 rpm and 101 deg F ambient outside temp.

I believe when I flushed the condensor originally, I failed to completely remove all the solvent.

I think a few oz of solvent collected in the built-in reciever/drier tube attached to the side of the condensor. I should have tried to remove the condensor to better remove the flushing solvent or done a better job making sure I removed all the solvent.

This particular problem took me a few months to solve








Edited: Sat September 15, 2012 at 11:48 PM by stuvx

AutoCool on Sun August 12, 2012 4:32 AM

Not sure what it says in your manual, but the compressor control valve is varied by voltage, not amperage. Not sure what you can measure with vagcom or what the dealer uses for control valve testing. I use a "CLT1" for testing. The control valve is easily plugged, VW says you should flush the evap and lines for 4 hours or something like that when you replace a bad compressor.

I've had some luck "unplugging" electronic control valves by cycling the control valve fully closed to fully open with the CLT1, I'm guessing that the valve was "flushed" by cycling it and the junk inside found it's way to the filter. Haven't had any callbacks yet on those cars. Maybe you should call around to indy shops and see if anyone has one? I'll check and see what mine actually does later and post so you can see what the voltage range is. That should also give you an idea what voltage you should be getting from the computer.

Have someone start the car and turn on the AC while you listen with the hood open, when these compressors start up it sounds a bit like a jet engine winding up.

BTW, you could also have a problem with your mixer flap motor. Have you checked trouble codes from the control panel? (push in ECON and RECIRC buttons at the same time) Code 4F7 is your blender flap motor, that has a red arm and you should see it when you remove your glovebox. Maybe the arm just came loose, they do "wiggle" a lot under normal operation.

stuvx on Sat September 15, 2012 11:57 PM

Fixed problem. I did a poor job of removing all the flush solvent from the condensor before putting everything back together.
Blew all the lines, condensor, and evaporator with compressed air again and drained the compressor.

Filled it again with PAG and refrigerent and am getting 45 deg F out the vents at 101 deg F outside temp. Low side pressure at a reasonable 30 psi now