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reflexryan on Tue October 23, 2007 12:36 PM User is offline

Year: 2002
Make: VW
Model: JETTA
Engine Size: 1.9
Refrigerant Type: 134
Country of Origin: United States

This problem is driving me nutz. I have checked all fuses in the door and all the ones under the hood .I have checked the fan control module and it seams fine .I have voltage at the compressor ,but it jumps around from what I read it is supposed to .However it does not seam powerful enough to get the clutch to engage. I have checked and jumped wires on the radiator switch and can get the fans to go on high and go on low. I think I might have messed something up when I jumped the clutch to 12 v .The clutch will engage at 12 to the battery,but when i did this i turned the car on and went to see if I had cold air when I herd the POP. The pressure relief valve on the compressor opened.Bentley says they will shut off after the pressure drops and it did.I thought i screwed up big time when I herd that pop ,but then again I still might have.I do have pressure in the low side but it reads in the 90s and I am not going to jump the clutch again to find out if it drop when the system is on since I know the system lose some pressure.I did jump the thrust switch in the back of the firewallnext to the expansion valve and the fans came on again,but I am not sure if the compressor is engaging and I don't want to go under the car and find out .. Well I am off to HF to go and get some gages to find out what the high side is running at.If any one can tell me why my relief value popped please let me know. Do these vw turn off the fans when the pressure is low or do i have another problem.
2002 Jetta TDI reflex silver

badufay on Tue October 23, 2007 1:05 PM User is offline

Another fellow VW guy!!! First, you aren't going to get far without getting a high pressure gauge as well. Right now I can tell you about half the people on this forum are probably assuming you bought a black death kit from Autozone and have the free low pressure gauge as your sole tool for diagnosing the system, but we (mostly they) can help. First off, I wouldn't recommend having the clutch jumped while you are starting the engine. You can jump it after everything is started and running, but make sure you turn the a/c on like you want it to run so the ECU can pick up the extra load and send the right signals to the fans. If everything is turned off, your high and low pressure should be about the same as the outside air temp, so if it is 80° F outside you should see something similar to that on both sides (static pressure). The fans will switch on if the pressure switches are detecting pressure to complete the signal and route it back to the ECU and the fan control module. Your pressure switch popped because at that switch on our cars it will if the pressure exceeds 580psi (i don't think you got that high, but could have if you clogged something with some stop leak). If the clutch is engaged the inside hub should be spinning. When you jump it (if you decide to), the ground wire is the brown/ green one, and the 12v should be green and black (should be!!). Get those readings and post your results here.


ice-n-tropics on Tue October 23, 2007 4:15 PM User is offline

Can't figure if you are really getting any voltage to the clutch. What's the voltage, if any, with the clutch coil in the circuit? Will the clutch engage if you press in the front plate with a smooth wooden handle while applying the inadequate voltage. Then do the fans go on and cooling starts?
One of my all big time stupid idiot jobs was to forget to reconnect the ambient temp sensor after removing a Jetta front bumper to change out the compressor. Cost me one of the longest most frustrating days of my life till I manually traced out every A/C wire. The sensor is mounted in the front bumper and the ATC A/C is dead without it connected. Slight chance that or a similar sensor connection or feedback is your problem if you have no clutch voltage. The German automobile engineers that require the bumper and condenser removal to swap a compressor need to turn in their diploma for a trash truck.
The pressure relief valve pops off refrigerant and oil at 550 +/- 50 psi.
Old IV guy

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

reflexryan on Wed October 24, 2007 6:49 PM User is offline

The compressor will not kick on unless the fans are running .I have ordered a new "fcm" fan controle modual and it should be here some time this week.My niebghor who is a hvac mechanic helped me recharge the system..You can tell the clutch kicks in when you jump it straight to 12 from the battery then you can watch the gages go.I can not tell the actuall preasue of both sides beacuse I have to jump the fans as well so that the compressor does not overheat.static preasure is 60 on low side and about 70 on high.We had to jump the clutch to do this and had to have the fans on by jumping the thrust sensor and could not get a true reading on the gages since the fans were on high.We evec the system and put the right amount back in.I have jumped just about every thing on this a/c sytem but i still do not get a good 12 volt with both fans running to the compressor.Iam starting to wonder if my clutch coil is goig bad ,but then agian I still do not have fans so that why the voltage is probably low.I have jumped the thrust sensor and can get the fans to turn on but it will not turn the compressor on.I copied this and did all these procedures,but still came up with nothing.

How to Diagnose A/C System On 2000 VW Jetta GLS
Posted 11/16/2005
By Jim Newkirk
“ The problem involved a 2000 Jetta GLS 2.8L manual A/C system with no compressor clutch operation. On this vehicle, the cooling fan and A/C compressor operation are controlled by the J293 fan control module, which is usually located in the driver's front corner of the engine compartment on the lower frame rail. The J293 module has both a 14-pin connector identified as the T14 connector in Volkswagen wiring diagrams and a four-pin connector identified as the T4a connector. ”

This summer has been a hot one, and I'm sure you have seen your share of air conditioning problems. Unfortunately, A/C systems have grown steadily more complex and difficult to diagnose.

The problem involved a 2000 Jetta GLS 2.8L manual A/C system with no compressor clutch operation. On this vehicle, the cooling fan and A/C compressor operation are controlled by the J293 fan control module, which is usually located in the driver's front corner of the engine compartment on the lower frame rail. The J293 module has both a 14-pin connector identified as the T14 connector in Volkswagen wiring diagrams and a four-pin connector identified as the T4a connector.

To diagnose this system, starting on the T14 connector:

1) Start and idle the vehicle. Select "A/C on" at maximum cooling and "blower on" at high speed.

2) Check for 12 volts at the T14 connector pin No. 8 (T14/8). This 12-volt signal comes from the A/C switch and requires both cooling fans on at low speed and compressor activation.

3) Check for 12 volts at pin T14/9. This voltage is a switched ignition source and will have 12 volts when the ignition is in the "on" position.

4) Check for 12 volts at pin T14/4. This is a constant battery source and should read 12 volts at all times from fuse S16.

5) Check for a good ground at pin T14/6.

6) Check for 12 volts at all times at the four-pin connector, T4a pins T4a/1 and T4a/3 from fuses S164 and S180, respectively.

7) Turn off the ignition. Remove the T14 connector and check for continuity between pins T14/14 and T14/5 on harness side to ensure proper operation of the F38 ambient temperature switch. Continuity must be present if the ambient air temperature is above 32 degrees Fahrenheit. Reconnect the T14 connector and restart the vehicle.

8) Check pin T14/2 using a duty cycle meter. If the refrigerant charge in the system is normal, about 30 percent to 35 percent duty should be indicated at pin T14/2 without the compressor engaged. The duty cycle signal is supplied by the G65 pressure sensor in response to system pressure changes. A duty cycle above 90 percent or below 20 percent will command the compressor off.

9) Check for an 11-volt reference voltage at pin T14/3. The reference voltage originates in the J293 fan control module and can be grounded by |the power control module (PCM) under certain circumstances (typically wide open throttle or vehicle overheat conditions) to turn the A/C compressor off.

If zero volts are present, the PCM is commanding "compressor off" or the wiring harness is shorted to ground. Raise vehicle idle speed above 2500 rpm and observe compressor operation and voltage at pin T14/3. If the voltage at pin T14/3 returns to 11 volts with the idle speed above 2500 rpm and compressor operation resumes, then a throttle basic setting procedure is needed and must be performed with a factory-compatible, by-directional scan tool. Note: A loss of throttle basic settings will keep the compressor from activating.

If all previous tests have passed, check the T14 connector pin T14/10 for 12 volts. This pin is the output signal to the compressor clutch coil. If all the other tests have passed and there is no voltage at pin T14/10, this indicates a faulty fan control module.

As you can see, turning on an A/C clutch is not a simple function on late model vehicles, and systems that you might not associate with an A/C problem can stop you and your customer from keeping cool. Be sure to check Direct-Hit's Hotline Archive section for more diagnostic procedures and tips.

Jim Newkirk is an Identifix European specialist. He is an ASE Master with L1 and Bosch BSC certifications. In addition to providing training for local and national automotive affiliations, Newkirk has appeared on a number of radio talk shows.


Chick on Wed October 24, 2007 7:19 PM User is offlineView users profile

Try this, once you get the system up and running to where the compressor will come on with the AC called for, evacuate the system, recharge the exact amount of refrigerant back in (By underhood sticker) then you can properly diagnosie your system,.. Use only virgin R134a, no sealers or additivres of any kind, with the exception of UV dye..

Your modual is most likely the problem, but don't add anything until it's working and then start from square one.. Your system is now low since the pop off valve popped, and the ONLY way to kniow if it's fully charged is to recharge it..Simple...Hope this helps.

Email: Chick


Freedoms just another word for nothing left to lose

mk378 on Wed October 24, 2007 10:50 PM User is offline

It was an electrical problem all along. Sounds like if you go thru the checks and all the signals to the module are proper, the module is bad. Get to where the compressor will engage with everything connected stock and at least a little refrigerant in the system, quit jumping stuff. Once you have that, recover all the refrigerant and recharge with the proper amount by weight.

Also check that there is no leaking from the relief valve, sometimes they don't reseat properly.

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