a/c compressor not engaging , Rad fans not going on

enatman · March 24th, 2012, 09:01

I checked everything on my 2000 jetta tdi automatic.

I noticed about three weeks ago I wasn't getting cold air when I turn on my a/c. the a/c light goes on, but no cold air. I did every possibly test on this forum. I replaced the FCM with a new one from ID parts. I checked the pressure with a refilling system and it says charged. The fans kick on high, but shut off immediately. BUT will not stay on when I turn on A/C

I checked the temperature switch under the plenum ..It works

I even purchased, but yet to install, the high pressure switch

Checked fans and replaced one, Both work when I put power to them

I checked ohms at high pressure switch and it seems correct.

What's left? I'm not getting the radiator fans to stay on when I turn on a/c and the compressor is not engaging?

Turkeywrap · March 24th, 2012, 09:42

Check the bat top fuse box, first green fuse, mine was burnt toasty.

enatman · March 24th, 2012, 19:34

Checked battery top fusebox and tested all fuses..No burned fuses

gquenstedt · March 24th, 2012, 20:14

If you already bought the high pressure switch, why haven't you installed it?

more than likely that is your problem.

AndyBees · March 24th, 2012, 21:20

Turn the ignition to ON (do not start engine), turn cabin fan on low and then push in the AC button. If everything is working properly, the two fans out front should come on low speed. Also, make sure that the on dash (cabin fan) is actually running and the AC buttom is light up. If the on dash switch has gone kaput, the AC system will not operate. Turning it on signals the FCM to turn on the fans and engage the AC Compressor Clutch, assuming you push in the AC button.

Have you hot wired the AC compressor clutch to see if it "pops" when activated?

There is a 4-pin electrical connector just above the starter and below the battery. That connector contains the two wires that go to the AC compressor clutch and the other two wires go to the Alternator. See if that connector is damaged! Also, as I am sure you know, there is a 2-pin connector at the AC compressor...check it for damage too!

Lastly, you might want to consider re-installing the old FCM.

Hope this helps!

enatman · March 25th, 2012, 12:39

The high pressure switch NEVER goes bad..i spoke with three people and they told me the design is so simple..It doesn't have room for fault..I jumped it..i Only bough this in case something lead to that..So far It doesn't

enatman · March 25th, 2012, 12:43

Andy..I did that..from day one...the dash switch is not an issue. i'm going to hot wire the a/c compressor and look at wire above starter... BUT started and battery are on opposite sides? I'm thinking perhaps, my low speed may be burned on the fan, and not the high speed (as tested).. I have been looking at why fans are not coming on when a/c is turned on...perhaps the combination of no low speed and the clutch going bad?

DanG144 · March 25th, 2012, 13:00

The high pressure SENSOR does go bad. You cannot jump it. It is not a switch after may of '99, but a pulse width modulated signal.

Check your radiator/condensor fans NOW.

enatman · March 25th, 2012, 17:56

A special thanks to Dan G.. My problem was... the pressure.. I was using a can of freon to check the system pressure.. It showed FULL... Not the case.. the can shows full at 25lbs.. When I filled to 27-30 the fans kicked on.. under 35lbs (depending on temp ect) is a good pressure.. Now I need to find the leak

gquenstedt · March 25th, 2012, 18:25

Did you replace the sensor?

As long as there is some pressure in the system, it should come on.

DanG144 · March 25th, 2012, 18:44

He did not replace the sensor. His pressure was too low for ambient temperature, indicating a loss of charge. When he added some refrigerant, it raised the pressure, it cleared the interlock and the compressor and fans started working.