Air Conditioning worked intermittently and stopped...

[SilverWagon]

I've read many threads on the mk4 air conditioning but nothing that matches my symptoms so I thought to get some guidance from you guys.

About a month ago I started to think there was an issue with my AC. First it started by staying cold most of the time with small periods of semi cool air coming through. Then it would switch back to cold for a while. Then this last week it was semi cool more than constant cold. It seemed to switch to cold when I would gun it but that might just be coincidence because I can't test it anymore. AC doesn't get cold anymore.

I noticed that both fans run with the ac on or off. When I park the car and turn it off the fans sometimes run for 20 seconds or so, turn off for a couple, and then run for 20 seconds. Sometimes the fans just run for for a while and then switch off. I haven't had time to time this.

I checked the fuses on top of the battery. Tomorrow I'll work on it more. Any suggestions?

 

[csstevej]

Have you thrown on a set of guages to see what pressures your running. You could be low on Freon. It’s based on weight in the system 700 grams + 25. But ball park is about 37-40 low side and I believe around 200-200 high….. might be off a little.
If pressures are about even with the compressor running it Could be a RCV being intermittent ( refrigerant control valve ). Located inside the compressor.
Don’t have to change the compressor to do it but you do have to remove the Freon to do it if that’s the issue.

 

[SilverWagon]

Have you thrown on a set of guages to see what pressures your running. You could be low on Freon. It’s based on weight in the system 700 grams + 25. But ball park is about 37-40 low side and I believe around 200-200 high….. might be off a little.
If pressures are about even with the compressor running it Could be a RCV being intermittent ( refrigerant control valve ). Located inside the compressor.
Don’t have to change the compressor to do it but you do have to remove the Freon to do it if that’s the issue.

No, I haven't yet. I only have a gauge that came with a freon tank I got a couple years ago. I attached it to the front (low I think) without the car running and it shows about 120psi. The gauge wouldnt attach to the connection (high I think) closest to the firewall. From what I'm reading on other threads Harbor Freight has a set of gauges that are affordable.

Every time I turn the car on, even without moving the car, the fans turn on for 15 minutes or so.

 

[Rxfire]

Fan Control Module went on mine, and fans would run after shutting engine off. Eventually, I got your symptoms. Not hard to access bolts from top, near battery tray, if you have a manual transmission. $25 part. Hardest part was getting both electrical clips undone from underneath

 

[csstevej]

Two things to try.
Inspect fuse #16 on the side console and see if blown.
Also make sure the the fuse got the fans on top of the battery are clean and shiny….no oxidation or corrosion on the fuse or the slots that the fuse goes into and report back.

 

[mrGutWrench]

Fan Control Module went on mine, and fans would run after shutting engine off. Eventually, I got your symptoms. Not hard to access bolts from top, near battery tray, if you have a manual transmission. $25 part. Hardest part was getting both electrical clips undone from underneath

Yep. I had to change my Fan Control Module about a year ago. I did the fan operation check (I think that there's a "stickie" post at the top of the A4 Forum) and the fans didn't work (at all, in my case). I had a couple of hundred thousand miles on them so I assumed it was a fan problem -- if the fans don't work, high temps will trip your override temp and pressure sensors in the A/C system. So I changed the fans and that didn't help. I put my multimeter on the compressor power wire and was getting nothing when my wife would switch on the A/C, engine running. I was in a hurry so I went to the local VW dealer parts department and got a quote for $739 plus $50 NC tax. I said "no, thanks", went home and got one the IDParts website. They have choices, my old brain is telling me "it's foggy, it's foggy! but I think they had 100% Original Equipment VW Spare Parts, an aftermarket sale of the OEM piece but not officially through VW's network, and a SE Asia knockoff". Anyway, DO NOT go to the VW Dealer and pay retail.
As Rxf says, you pull the battery, then four screws holds the battery box in. When that the battery box is removed, the FCM is sitting there. There are a couple of multi-terminal connector blocks. Pull the two fixing screws out (or they might be bolts, not sure, but same deal), change over the connectors and reinstall the fixing screws, but the battery box and battery back in and that's done.
But do the test for battery voltage at the compressor and get your "freon" pressures checked before you assume that it's the FCM.

Good luck.

 

[noob_tl]

No, I haven't yet. I only have a gauge that came with a freon tank I got a couple years ago. I attached it to the front (low I think) without the car running and it shows about 120psi. The gauge wouldnt attach to the connection (high I think) closest to the firewall. From what I'm reading on other threads Harbor Freight has a set of gauges that are affordable.

Every time I turn the car on, even without moving the car, the fans turn on for 15 minutes or so.

If the fans and compressor run but the system won't cool down the RCV is a likely suspect. Even with just the low side gauge you have you can test. Hook it up to the low port, get the reading (120psi you read above) then start the car and turn on the AC. If the pressure doesn't drop significantly (usually in the 40's) then the RCV is probably stuck.

You do have to have the system evacuated and remove the compressor to replace the RCV, but it comes out pretty easily from the bottom. I just did this a few weeks ago with a kit from CoolairVW and it brought my daughter's '03 NB back to functional. He has a video on the procedure.

I have the HF gauges and they worked good at first, but the hoses decay pretty fast. My yellow hose blew while recharging my son's car when the set was about 2 years old. The blue and red hoses are looking pretty bad now as well, too. Around here Autozone has gauges and vacuum pumps on their loan-a-tool program.

 

[Rxfire]

bolts that hold Fan Control Module are shown on page 12 of this write-up (accessible without removing battery/battery tray-a 1/4 inch drive with long extension helps):

https://pics.tdiclub.com/data/517/A4_Air_Conditioning_Troubleshooting_Rev_7.pdf

 

[SilverWagon]

Yesterday I checked the low with the gauge I have and it showed 108psi with the car on, off, and with the ac or off. I tried to relieve some preasure and got it down to about 100psi. This morning I drove it to work and the AC turned on. Then it turned off while driving.

I'll troubleshoot using all of your suggestions and report back. Thank you

 

[03TDICommuter]

Yesterday I checked the low with the gauge I have and it showed 108psi with the car on, off, and with the ac or off. I tried to relieve some preasure and got it down to about 100psi. This morning I drove it to work and the AC turned on. Then it turned off while driving.

I'll troubleshoot using all of your suggestions and report back. Thank you

Not sure where you are in California but it's been hot where I am (Ventura - Santa Barbara) and 108 PSI is just over 90 deg F outside. So that pressure would be fine and you shouldn't bleed it off. Likely undercharged now.

 

[SilverWagon]

Two things to try.
Inspect fuse #16 on the side console and see if blown.
Also make sure the the fuse got the fans on top of the battery are clean and shiny….no oxidation or corrosion on the fuse or the slots that the fuse goes into and report back.

Fuse 16 is fine. Fuses on top of the battery are shiny. The psi went down to 90 this morning when I was checking it. It turned on for a moment and then off.

 

[SilverWagon]

bolts that hold Fan Control Module are shown on page 12 of this write-up (accessible without removing battery/battery tray-a 1/4 inch drive with long extension helps):

https://pics.tdiclub.com/data/517/A4_Air_Conditioning_Troubleshooting_Rev_7.pdf

I took a look at the Fan Control Module and noticed that the previous owner had to fix or did something with one of the wiring harnesses connected to FCM; the harness with 12 to 14 or so wires. 2 of the wires had been cut and extended by 5 inches with a new wire and simply twisted together.... The connections were dirty and one came apart when i was inspecting them. I got some heatshrink butt splice connectors, cleaned off the wire ends, and reconnected the wires securely.

I tried the ac for a couple of minutes and it worked. The fans do not stay on when I turn the car off so something has changed. If that didn't fix the the problem I'll report back.

I wish I had butt splice connectors I could solder with but this should hold up for a long time.