AC Compressor won't engage

brett.knutson

Member
Joined
Mar 21, 2008
Location
NOVA
TDI
2002 Jetta TDI
Hopefully someone can help me out... Due to a military deployment, my '02 Jetta TDI sat for several months without being driven. When I returned, it started right up (after a jump start) and ran perfectly fine, except no AC.

The console button illuminates, the cabin fan blows, and the radiator fans both operate, but the compressor doesn't engage.

I ran battery voltage to the compressor and the clutch does click.

I tested the coolant temp sensor and the fans will run properly (both low and high speeds).

The high pressure switch connector has 12 vdc at pins 1 and 3.

After all those tests, could it still be the Fan Control Module? Or, is there another test I can try, without having any pressure gauges?

Should I try to add a can of R-134?

Any assistance or recommended gurus in the Northern VA area would be greatly appreciated...
 

chromeBuddha

Veteran Member
Joined
Jun 30, 2006
Location
Arlington, TX - DFW metroplex
TDI
2002 Golf TDI manual
You can bridge the pins on the high pressure switch and see if the compressor clutch clicks in...

With the compressor not running, you ambient pressure should be around 100 PSI. If you check this and the pressure is next to nothing, you may have a leak and your coolant may have leaked out. Your electrical testing seems like it has covered most of the bases.
 

KLXD

Top Post Dawg
Joined
Aug 22, 2009
Location
Lompoc, CA
TDI
'98, '2 Jettas
Don't these systems have a low pressure switch to keep the compressor from running with no refrigerant in the system?
 

gquenstedt

Veteran Member
Joined
May 26, 2006
Location
San Antonio, TX
TDI
'06, '03 x 2, '00
You can bridge the pins on the high pressure switch and see if the compressor clutch clicks in...
NO NO NO!

This is not a 1987 Chevy we're talking about.

Usually if the fans come on when you turn on the a/c, then the FCM is getting the go ahead from everything that it needs to turn on the a/c, but is just not sending power to the clutch coil. I would replace the FCM with one from a reputable vendor. NOT ebay.
 

chromeBuddha

Veteran Member
Joined
Jun 30, 2006
Location
Arlington, TX - DFW metroplex
TDI
2002 Golf TDI manual
NO NO NO!

This is not a 1987 Chevy we're talking about.

Usually if the fans come on when you turn on the a/c, then the FCM is getting the go ahead from everything that it needs to turn on the a/c, but is just not sending power to the clutch coil. I would replace the FCM with one from a reputable vendor. NOT ebay.
The bridging of these pins to test the high pressure switch is in the Bentley manual. I will get the section and page # if that will put you at ease.

Brett,
I believe it would be pin 1 to 2, meant to confirm in the manual last night but was whipped. Will check it tonight.

In re-reading, I meant the pins on the connector, not the switch. Bridging anything on the switch with it disconnected wouldn't accomplish much...
 
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DanG144

Top Post Dawg
Joined
Aug 2, 2007
Location
Chapin, South Carolina, USA
TDI
2005 A4 Jetta 5spd
The bridging of the pins is for models before May of '99, which had a dual hi lo pressure switch on the high side, and four pins.

Do not try to bridge a 3 pin high pressure sensor used after May of '99. At best you will blow the fuse.
 

brett.knutson

Member
Joined
Mar 21, 2008
Location
NOVA
TDI
2002 Jetta TDI
I don't think I am getting voltage to the compressor coil at all... It will definitely click when I apply 12v directly from the battery but nothing when I have the car running w/ ac 'on'.

Sooo, how confident are you guys it is the FCM? How much would one be, and where is a good place to get one? I would like to get this resolved tonight if possible.
 

gquenstedt

Veteran Member
Joined
May 26, 2006
Location
San Antonio, TX
TDI
'06, '03 x 2, '00
I don't think I am getting voltage to the compressor coil at all... It will definitely click when I apply 12v directly from the battery but nothing when I have the car running w/ ac 'on'.

Sooo, how confident are you guys it is the FCM? How much would one be, and where is a good place to get one? I would like to get this resolved tonight if possible.
If the coil is good as you suspect, and when you turn the ac on and off the radiator fans turn on and off, then your pressure sensor is good and the only thing it can be is the FCM. You can always get one at the dealer if you're in a hurry but you'll pay a lot. Www.autohausaz.com www.boraparts.com or www.idparts.com are all good
 

brett.knutson

Member
Joined
Mar 21, 2008
Location
NOVA
TDI
2002 Jetta TDI
The fans seem to always run on low speed, but if I jumper at the coolant sensor they will go to high speed... How can I test the pressure sensor?
 

brett.knutson

Member
Joined
Mar 21, 2008
Location
NOVA
TDI
2002 Jetta TDI
I just pulled the FCM off, it looks fine. No corrosion, nothing melted, all connections clean and dry. Is there a way to test it?
 

gquenstedt

Veteran Member
Joined
May 26, 2006
Location
San Antonio, TX
TDI
'06, '03 x 2, '00
I just pulled the FCM off, it looks fine. No corrosion, nothing melted, all connections clean and dry. Is there a way to test it?
1. Turn the ignition to on, but do not start the engine.

2. Turn the a/c on. Do the radiator fans come on low speed?

3. Turn the a/c off. Do the radiator fans turn off?

If so, that means that the FCM is getting all the right signals to power up the clutch, but it is just not sending it power because it is broken. You can not tell by looking at it.
 

brett.knutson

Member
Joined
Mar 21, 2008
Location
NOVA
TDI
2002 Jetta TDI
the fans come on even with the a/c off, and stay on for awhile even after the key is turned off. SOunds

I just bought one from boraparts for $56... wish me luck.
 

DanG144

Top Post Dawg
Joined
Aug 2, 2007
Location
Chapin, South Carolina, USA
TDI
2005 A4 Jetta 5spd
If the fans are coming on with the AC off, and staying on with the key off, check your fuses for your system.

You have lost one of the power signals. Bad fuse or bad wire.

Fuse 15, I think.

I did not post this earlier, because some of your wording seemed to suggest you had already found it, but have you done the troubleshooting
http://forums.tdiclub.com/showthread.php?t=242699 found in post #1 of this thread?
 

brett.knutson

Member
Joined
Mar 21, 2008
Location
NOVA
TDI
2002 Jetta TDI
The fuses were the first thing I checked... all were fine. And yes, I did follow the steps in that post.

With my fans acting screwy like they are, it seems logical to me the FCM might be going. If not, I'll sell it on ebay and bite the bullet and take the car to an a/c guy.
 

DanG144

Top Post Dawg
Joined
Aug 2, 2007
Location
Chapin, South Carolina, USA
TDI
2005 A4 Jetta 5spd
Closely inspect the wiring going into your FCM. Several people have found broken wires there.

With this type of problem, taking it to an "A/C guy" is an almost certain guarantee of frustrating expenses.

Try this as well.
Unplug your High pressure sensor and see if the symptoms change.
 

brett.knutson

Member
Joined
Mar 21, 2008
Location
NOVA
TDI
2002 Jetta TDI
I checked and re-checked all of the fuses, in the cabin and on the battery, all are good and have no corrosion.

Doesn't the FCM send a power signal to the compressor also?
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Yes, the FCM does send "current" to the AC clutch. On the OPs 2002, the FCM has two connectors (a 14 pin and 4 pin). Pin T14/10 carries current to the AC clutch (N25 per the Bentley). The AC Clutch circuit is not fused after leaving the FCM. The FCM gets it's power from pins 1 & 3 of the 4-pin connector from a 6.0 size wire from Fuse S184 (40amp) and a 2.5 size wire from Fuse S180 (30amp, the left green fuse) at panel on top of battery. Pin 4 of the 4-pin connector "powers" the high speed of two fans. Pin 2 powers the low speed of the two fans.

Same thing happened to me 5 years ago. My Jetta sit parked for about 7 weeks while I was getting over major surgery.

Long story short ...........the outside Temp sensor wires had been chewed off by a mouse. The sensor is located behind the cowl below the left corner of the windshield. You will have to remove the wiper arms and then work out the plastic cowl to reveal the Outside Temp Sensor.

Also, a bad old or "new" Fan Control Module will look just fine on the outside but be trash on the inside ....... I installed a "new" FCM and new fans a couple of weeks ago. The AC clutch would not kick-in. I put the old FCM back on and the AC clutch worked just fine...but no fans. So, for the moment, using the bad "new" FCM, I have my AC clutch hot-wired off the low speed wire of the large fan. For AC purposes, it works just fine!

EDIT: My "Bad" NEW FCM come from a reputable vendor on this web site ...........second bad one! Only problem, I've had it since late last fall but only installed it a couple of weeks ago. Hint: It was one of those $39.95 ones ..........I'll never purchase another one of them!
 
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brett.knutson

Member
Joined
Mar 21, 2008
Location
NOVA
TDI
2002 Jetta TDI
well, I already bought a new FCM... and might have caught a break on it. I paid for the aftermarket $56 model, but got a message today saying they shipped an OEM one. Pretty sure the OEM one is over $200 at the dealer.

I'll stick the FCM on, if that doesn't do it I guess I'm digging for the outside temp sensor.

BTW, nothing changes when unplugging the high pressure sensor.
 

Dave_D

Veteran Member
Joined
Jun 9, 2003
Location
Gaithersburg, MD, USA
TDI
2015 Passat Titanium Beige six speed manual & Jetta, 1999.5, Tornado Red
I second the suggestion of checking the wiring between the FCM and the a/c clutch. In my case I found a broken ground wire at a connecting block between the two was causing my problems.

Dave
 
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