AC Compressor? acting stangely

Lance Allison

Requiesce In Pace October 20th, 2019
Joined
Jul 28, 1999
Location
Central Illinois
TDI
98 Jetta, Classic Green
The AC compressor on my 98 Jetta has been acting strange lately. It works great once the car is moving, but at idle, the compressor will kick in for maybe 2 or 3 seconds, then stop for a long time >30 sec. I know compressors normally turn off and on, but there is almost no cooling in the car at idle.

The system has a good R134a charge, reading about 33psi on the low side. The air output temp when driving is in the high 40 degree range, so it is plenty cool.

I've noticed that after driving for awhile and then returning to an idle (like in the garage), this does not happen.

Any ideas?
 
M

mickey

Guest
Are the cooling fans running when the car is stopped? When the refrigerant pressure hits a certain point the fans are supposed to turn on. If they don't, the pressure will continute to rise until the A/C compressor is locked out to protect it from excessive pressure.

When you're going down the road there is enough air moving through the condenser to keep the pressures on the suction side down to an acceptable level.

I suspect your fan relay is kaput. Check the fuse, too.

-mickey
 

Drivbiwire

Zehntes Jahr der Veteran
Joined
Oct 13, 1998
Location
Boise, Idaho
TDI
2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
On the TDI A/C compressor it should NEVER shutoff when the A/C button is engaged. THe pump can vary its output to control the amount of freon it's pumping. At times it can vary the amount to zero or 100% volume depending on the evaporational demands of the system.

If the pump is cycling off as you describe it could be like Mickey said that the system is detecting and overtemp or over pressure and shuts down to prevent damage.

You may want to check the Fan control relay since this has primary control of the fans and is directly in control of the A/C compressor. The reason is it checks to make sure there is fan operation and once that is satisified then it will allow the compressor to engage via the compressor clutch.

DB
 
M

mickey

Guest
If the fans are working, the pressure switch itself could be faulty.

-mickey
 

Lance Allison

Requiesce In Pace October 20th, 2019
Joined
Jul 28, 1999
Location
Central Illinois
TDI
98 Jetta, Classic Green
Well, I checked the fans, they are working as they should. On an aside, I kept the gauges hooked up and monitored the pressures on the low side.

When the compressor is running, the low side pressure is between 35 and 40psi. When it kicks off, it goes to about 60psi, then drops back to the 30's when the compressor kicks back in.

Without looking in detail, I wasn't able to find the pressure switch...any ideas where it is on the A3's? And what is the best plan of attack to change it out...
 
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