# a/c not working, diagnostic steps?



## John A (Feb 19, 2001)

the a/c in my 2k1 jetta 1.8t isn't working -- just never gets cold...
tried to add a can of refrigerant, but it wouldn't take it...
it doesn't seem like the compressor is turning on -- even though vag-com shows AC HIGH and compressor on when i switch it on....
i'm assuming that the refrigerant is low, and that is keeping the compressor from turning on -- but it also won't take any without the compressor going on.
normally we'd just jump out a switch and force the compressor on, but i couldn't figure out how.
any ideas? anything else i should be checking?


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## John A (Feb 19, 2001)

*Re: a/c not working, diagnostic steps? (John A)*

bump!


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## Mike0105 (Dec 31, 1999)

*Re: a/c not working, diagnostic steps? (John A)*

no clue John...might want to give chris or pat a call and ask them for some help
Mike


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## John A (Feb 19, 2001)

*Re: a/c not working, diagnostic steps? (VWMike81)*

yeah... this one's going to be ugly i think. i guess a/c isn't part of powertrain, eh? maybe it's time to trade it in.


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## oldskool industries (Oct 18, 2002)

*Re: a/c not working, diagnostic steps? (John A)*

Hey John,
My Wife's New Beetle has just been bitten by a similar thing- except when I press the AC button, the AC compressor doesn't come on and Vag-com aggrees-- the compressor is shown as off.
I was cruisin the Bentley this evening and it looks like there are a few hidden switches in there... one will not let the compressor turn on if it's too cold, and the other won't let it turn on if there is too much/ too little refridgerant in the system.
There's a quick test to be made, by jumping pins 1 and 2 of the sensor in the far back passenger side of the engine compartment. I couldn't reach it real easy tonight (had a flashlight in one hand), but I'll see if I can get to it tomorrow.
http://****************.com/smile/emthup.gif 
-chris


_Modified by oldskool industries at 12:14 AM 5-5-2003_


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## Bug_Power (Nov 27, 2000)

*Re: a/c not working, diagnostic steps? (oldskool industries)*

Ok I just did this the other day.....
Jump out and check if when you turn the AC on if your compressor turns on or the Fans? If not. Check the PLUG that comes off the top of the battery you should be able to use a test light and should get 12v from all 3 or 4 pins (think it's 3). If you have power there, those wires run striaght to your relay which is under your battery. It's pretty big costs about $170 if it's bad. If the blower comes on it's going to be one of those or the compressor. Turn the AC on and test light the plug for the compressor, you should see 12v. If not, it's one of the things listed. Also check your high and low pressure switches if they are bad the compressor will not turn on, However check the other things I mentioned earlier first. ALso there is a temp switch that is in the same area of the car as the relay. It's a big sensor that is on the radiator endcap I think. Check for 12v there. That basically sums up the WHOLE AC electrical system for the compressor.


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## Bug_Power (Nov 27, 2000)

*Re: a/c not working, diagnostic steps? (Bug_Power)*

let me know what you find


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## John A (Feb 19, 2001)

*Re: a/c not working, diagnostic steps? (Bug_Power)*

we tried jumping out what i thought was a pressure switch near the firewall on the pass side this past weekend. we proceeded to blow a fuse, and stopped going down that route. i'll see what i can find out this week.


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## mk4007 (May 23, 2002)

*Re: a/c not working, diagnostic steps? (John A)*

1. check to see if your AC compressor is engauging. If it isn't it's either 2 things, there is not 134a in the system because of a leak, or you have a bad relay. Before wasting your time checking relays, take a small screw driving and quickly push in/out on one of the high side or low side lines (just unscrew either the big or small cap on the ac lines. If a weak mist comes out, your system is probably empty due to a leak, if a quick burst comes out it's probably full and you have an electrical problem.
If there is no 134a check for the obvious, a hole in your condensor (infront of the radiator) all it takes is a small pebble at 100mph to put a hole in it. Look for oil spots and paint coming off on spots on your condensor, if you get a 134a sniffer it will be alot easier. If you can't find any leak you're going to have to get a certified shop to put die in the system.
If there is 134a start by checking all the fuses. If there good switching the AC compressor clutch relay with one just like it and see if the compressor turns on. If it doesn't, get the ETM and jump the relay, if it doesn't turn on, there is either a wiring problem after the relay, or in the Electrical part of the comrpessor clutch. If it does turn on, the problem is either the relay, or an electical problem before the relay (wiring, switch)
Hope this helps. Don't smoke when you're checking to see if there is 134a








marty


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## John A (Feb 19, 2001)

*Re: a/c not working, diagnostic steps? (mk4007)*

i'm hopefully going to do some of these steps tomorrow, will report back...


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## Acerxz (Aug 7, 2000)

*Re: a/c not working, diagnostic steps? (John A)*

I have the same problem, nothing happens when i push the a/c button. I also have the same problem with the cruise control.


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## Bug_Power (Nov 27, 2000)

*Re: a/c not working, diagnostic steps? (Acerxz)*

Guys I looked at 3 other NB's today and all but the newer 2002 had the power distribution panel on the top of the battery was just fried. Had another buddy that the relay went out in his car yesterday. Similar symptoms. Blower blows, just no cool air. Clutch doesn't engauge and now power to compressor. Traced it all the way back to the relay. Power going to relay, and switch was being turned on, just relay wasn't clicking on.


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## John A (Feb 19, 2001)

*Re: a/c not working, diagnostic steps? (Bug_Power)*

first update: system has pressure, i touched the valve with something and it shot out at me.... 
distribution block was fine, all fuses were good and looked fine.
where is the relay? i can check that tomorrow....


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## Bug_Power (Nov 27, 2000)

*Re: a/c not working, diagnostic steps? (John A)*

relay is directly under the battery....I really think it's that because your not getting power to the Fans or the compressor right? When you turn the AC on high your fans for the radiator don't turn on high? Relay will be really big with 2 plugs going into it. I think on has like 7 wires while the other has 4 heavy gauge wires.


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## John A (Feb 19, 2001)

*Re: a/c not working, diagnostic steps? (Bug_Power)*

took out my airbox and battery today to find the relay, but came up empty handed.... here's a pic:








where's the relay ?



_Modified by John A at 9:16 AM 5-11-2003_


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## Bug_Power (Nov 27, 2000)

*Re: a/c not working, diagnostic steps? (John A)*

You get to it from the bottom of the car. Should be Under there, but from the bottom of the car. Follow the plug connector down from the top of the battery distrobution panel should go right to it.


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## gti1.8tony (Nov 9, 2002)

*Re: a/c not working, diagnostic steps? (Bug_Power)*

bug power is talking about the fan control module it is possibly faulty but first remove the fuse on top of the battery some times they will show voltage but will be blown inside the fuse its hard to explain but it will look melted you should back probe the a/c wir with 12 volts and see if it engages and does it they blow cold if not you could be low on freon the system wont work with a low charge


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## CRD99 (Oct 29, 2000)

*Re: a/c not working, diagnostic steps? (gti1.8tony)*

You may also want to check the low pressure sensor. I forgot to plug mine back in after installing my FMIC this winter. The fans would run but the compressor never engaged because the sensor is designed to protect it in case of a leak.


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## John A (Feb 19, 2001)

*Re: a/c not working, diagnostic steps? (CRD99)*

ok, i get no fans, no compressor. i'll get under the car tomorrow to look for it.
thanks!


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## Bug_Power (Nov 27, 2000)

*Re: a/c not working, diagnostic steps? (John A)*

Before you get under the car. Hook the battery back up, then unplug the connector that goes into the power distro box on top of the battery. Use a test light to make sure ALL of those pins are hot. If they are....the next stop is the Fan Relay under the battery that must be accessed from under the car.


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## John A (Feb 19, 2001)

*Re: a/c not working, diagnostic steps? (John A)*

fixed! see here:
http://www.abella.net/vw/acrelay.html
http://****************.com/smile/emthup.gif


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## Bug_Power (Nov 27, 2000)

*Re: a/c not working, diagnostic steps? (John A)*

Good to hear you got it fixed. Now if you have the equipment, you can clean that one up and get it working again. If your just going to throw it away, you may be able to get a couple bucks for it. When putting it back together just use some silicone RTV to seal it all up.


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## oldskool industries (Oct 18, 2002)

*Re: a/c not working, diagnostic steps? (oldskool industries)*


_Quote, originally posted by *oldskool industries* »_Hey John,
My Wife's New Beetle has just been bitten by a similar thing-

Ours turned out to be a cracked condenser. We had a rodent commit suicide thru our grill last year and his impact must have put a slow leak in the compressor.
I'm waiting for her new 'cup car' bumper to arrive before I fix it so I can take apart the nose of the car once.


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## John A (Feb 19, 2001)

*Re: a/c not working, diagnostic steps? (Bug_Power)*

thanks again rodney, this was a good thing to avoid a trip to the dealership on. (although my cracked coilpack wires -- now THAT it's going in for!) 
bump for the weekday crew.


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## flanders (Apr 5, 2001)

*Re: a/c not working, diagnostic steps? (John A)*

brutal.
glad to hear it's fixed! nice how-to http://****************.com/smile/emthup.gif


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## fetter (May 6, 2011)

John A said:


> fixed! see here:
> http://www.abella.net/vw/acrelay.html
> http://****************.com/smile/emthup.gif


Any chance you might be able to repost this? I have a 2002 Jetta that I think has the relay switch problem. Leads off the battery are hot, but the compressor is not getting any juice to it. Can't quite seem to figure out where the problem might be between the battery and the compressor.


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## fetter (May 6, 2011)

fetter said:


> Any chance you might be able to repost this? I have a 2002 Jetta that I think has the relay switch problem. Leads off the battery are hot, but the compressor is not getting any juice to it. Can't quite seem to figure out where the problem might be between the battery and the compressor.


OK, I found this write up on your website, however, exactly where is the fan control module located on a 2002 jetta?


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## radlynx (Jan 4, 2007)

fan control module part# 1jo919506k. search it at www.ecstuning.com. you'll see how it looks like.



fetter said:


> OK, I found this write up on your website, however, exactly where is the fan control module located on a 2002 jetta?


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## ModsTTand (Jul 8, 2009)

thanks for this elect. wiring diagnosis, it pretty much sum it up and made it easier knowing what to do in ur own garage if u have a tester 
:thumbup:


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## beachparty (May 27, 2010)

*Same problem..*

Hi !

I have the same kind of problem with my 1.8T 2003 Jetta.
However, I noticed that my fans are no longer coming off when the temp is coming high. Is this related and is it due to a bad Fan control module ??

Thanks for your advices

Cheers


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## brett1220 (Mar 16, 2011)

my AC doesnt work also but its not the compressor or the or any mechanical problem, its because the rubber line that comes from the compressor has been rubbing the the rad fan support for years and it eventually rubbed a hole in it so is their anyway i can patch it up?


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## melonhead (May 31, 2012)

*new pre-loade compressor*

Hi, 

I have a 2000 Jetta TDI that had a bad compressor. I bought a pre-loaded compressor this winter and installed it. I changed all my o rings, my evaporator and my expension valve. 

When I press on my ac button, the compressor won't engage at all. Since it came with the oil already in it, I don't want to add any more. How can I add "air" into it to build up the pressure? Seems like it doesn't see that it's full already. 

Thank you for your help.


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## Funky_Monkey (Jan 8, 2006)

Well, I had the pleasure of leaving work on a 95+ degree day this afternoon... only to find out my AC was not working 

after checking fuses, both on the side of the dash and on top of the battery, 

I pulled the battery out to look at the fan control module, which i pulled apart to find a lot of rusty stuff in there so i sprayed it with electrical cleaner .. tested it... it worked fine, so i rtv siliconed the cover back on... but my compressor would still not kick in:banghead: 

for some reason, i was impelled to wiggle the 3 green fuses that sit above the battery, when i heard the auxiliary water pump turn off and on 

I was like WTF?!?!?... so i pulled the fuse to find that one of the legs of the fuse was totally corroded ... i cleaned it up... fired up the car , turned the AC on AND SON OF A BITCH the AC worked:wave::what: 

not saying that this would fix all of yours problems, but it fixed mine


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## 02GTI1.8L (Jun 3, 2012)

i had a similar issue. i just spent 400 dollars on AC parts and had it recharged with die an all at work (im a tech for international) then my fiance was driving the GTI home last night and it never got cold compressor never kicked on i was ready to kill something then this morning i googled the problem and this site came up. i went out and pulled the fuses on top of the battery and sure enough even though they check out good by looking down on them from the top one of the legs had a little corrosion i cleaned it up and sure enough compressor and everything kicked back on. i do however have a coolant leak by the water outlet on the right side of the head i need to address now.


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## rcvwvortex (Aug 13, 2013)

*Electrical harness under the battery plate.*

I'm suspecting a bad Fan Controller Module on my 2004 Jetta 1.8T. Fans are running fine but the clutch doesn't engage. I got 9.6V measurement on the AC Clutch power connector. So there is power however is it enough to activate the AC Clutch? It should be 12V correct?

I'm trying to remove the Fan Controller Module but I can't find the mounting bolt under the battery plate. There's a bunch of electrical harness covering the mounting bolts. They're pretty tight, how did you move the electrical harness out of the way to remove the mounting bolt of FCM? Please click on the link below for reference. Thanks!

http://forums.tdiclub.com/showthread.php?t=281684


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## Brake Weight (Jul 27, 2006)

So my car sat in an open parking lot in South Mississippi heat for 29 days. I finally get back to it and do the walk around-all is visually fine. Fire it up and go to pay the lady to leave and there's no AC. The local forecast is 103*, real feel 120*. So I bail and head home. No overheating issues aside from myself. 

So today I read up some and troubleshoot what I can in this hellish searing heat. All fuses are good, compressor doesn't spin with the belt driving it-but I can by hand, and the one fan on the drivers side doesn't come on. I haven't read anything on only one fan running that I remember. Only fans on high speed, low speed, or not at all. 

Anyone with knowledge of the AC system?


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## cbradiospronto (Oct 15, 2014)

*low voltage to clutch*

I show 4.5 volts going to the a/c clutch. 12.7 coming out of the distribution block above the battery. Before I try to find the relay and test it, can somebody give me an educated guess as to what the low voltage reading is caused by?


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## grande78 (Oct 3, 2008)

http://forums.tdiclub.com/showthread.php?t=242699&highlight=DanG144 try this pge


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## mike_rmc (May 11, 2002)

New Beetle went from intermittent A/C one summer to no A/C the next. Unplugged the Fan Control Module, plugged it back in. Has worked ever since. Loose or corroded connection probably.


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## tbake01555 (Jul 18, 2014)

I had a similar issue, no power to the clutch or the fans when the a/c button was pressed inside the cab, and all of the diagnostics indicated a faulty fan control module.

I replaced the fan control module with several, including one I know worked on another car. None of them worked. I also replaced the pressure switch and ambient air switches. I checked the system, good pressure. A/C clutch engaged when jumped. 

My cooling fans were actually bad, and were not coming on low speed. When I found that problem, I thought I had solved the issue. Not the case, but I did replace the fans before they completely failed. 


I then broke down and started tracing the wiring. Using my bentley manual and a voltmeter I check continuity on just about the entire A/C system. I found two circuits with no continuity from the pressure switch. There was definitely some bad wiring somewhere, so I started cutting open the harness looking for something obvious. All the wiring that I can see looks good, all the way up into the dash where there is, apparently, several wiring harness junctions. I pulled most of the underside of the drivers dash off and I could see the wiring, and I could see what looked like a connector but I never actually found several connectors that were supposed to be under the hood, so that made things even more difficult. Anyway at that point I decided to take a step back and think about it a different way. To get to those wires under the dash I was going to have to pull the dash out of my daily driver. It wasn't practical so I decided it was a last resort.

I started researching how the A/C compressor works, and why it's not possible to just hot wire it and the cooling fans from the switch in the dash. I realized that I couldn't hot wire my A/C because I needed a pressure switch to control the compressor, not just a 12 volt signal. So then I came to realize I could use a generic suitable trinary switch to do exactly what I need, I just had to find one that would fit my pressure switches bung and that had appropriate pressure thresholds. Somehow I came upon that the 1999 vr6 used a simple trinary pressure switch. I bought one and installed it, and ran the wiring. The 99 vr6 trinary switch sent it's power to the fan control module, but looking at the wiring in the bentley the fan control module directly applied power to the compressor (and low speed cooling fans) when the pressure switch powered it, as long as every other switch in the system was allowing the circuit to close (ambient air, WOT). Basically the fan control is the A/C relay, among other things...

The trinary switch has four wires. One is a 12 volt signal from the a/c switch in the dash. This 12 volt signal supplies power to the compressor clutch as long as the pressure of the system is neither too high or too low, it is both a low and high pressure switch. The ranges are close enough to the factory ranges for my compressor that it was acceptable for use. The other two wires control the high speed cooling fans. The low speed should come on as soon as the compressor engages, so I used a relay to accomplish that. When the compressor gets power, the low speed cooling fans power up as well. When the system hits ~215 PSI, the trinary switch actives the high speed fans. That is controlled by another circuit in the switch which has it's own 12 volt power wire and a wire that sends power to turn on the high speed cooling fans. So there are two power wires, one is hot all the time (ignition) and the other is only hot when the a/c switch in the dash is pressed. You could easily wire in any safety switches you might want, such as wide open throttle or ambient air switches, I chose to omit these but I'm not going to run it to red line with the a/c on and I'm not planning on using my a/c when it's below freezing outside. 

To control the fans I used relays. The trinary switch activates the a/c compressor directly, but both the low and high speed cooling fans are powered independently and simply activated by relays that the switch controls.


I know this is extreme, but after reading several peoples post with similar problems and no solution, no fans and no a/c clutch engagement when the dash button is pressed, I had to get unorthodox. If anyone sees a problem with what I did or wants me to clarify I'd be glad to. I know that now when I push the a/c button in the cabin the a/c turns on and gets COLD!


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## nrotteveel (Jan 27, 2015)

Just had the same issue with my 2005 1.8t jetta. I checked the voltages on the fuses on top of the battery. appeared to be fine. But decided to remove the 3 green fuses (S178, S179, and S180). Low and behold, there was corrosion on the S180 that controls the fans. Just removing it and reinserting got the fans and AC to kick on. Cleaned up the corrosion further, but before tearing apart the AC and changing the relays and temp sensors, make sure the S180 fuse which powers the fans is clean.


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