A/C issues

99.5 TDI Jetta- A/C blows great at beginning, then after about 1hr or so at highway speed, the system seems to lose its strength. Air is semi-cold coming out, the fan is turning at all normal speeds, but it seems as if the air is being redirected or something is not allowing the air to come out at full force. This also happened with the heater/defrost on. I'm thinking something w/compressor? I tried turning to heat, but didn't help...the wife just complained more. However, after letting sit overnight works fine. This is an ongoing issue that repeats itself, but only on longer trips, no problem in short city driving...Any suggestions..thx.

Having same issue with my 99.5 Golf. The system will cool down to 35F and the fan blows nicely. It works great around town and short commutes, but after about an hour or two, my temp will be up to around 60F and output is down from the blower fan. It does run on all speeds, but I have to go to the highest setting to keep the air moving. Then, after awhile, the temp will drop to around 50F and the output will seem somewhat normal.

I turned the key on and verified that both radiator fans are working, but I've wondered if the interior fan might be wearing out, heating up, and slowing down. I just drove from MS to Little Rock and got to enjoy the warmer temps in my car for about 3.5 hrs. I've read many, many posts but none seem to address this particular issue.

Here's the link to my original post.

AC problem

Your evaporator is freezing up. Don't turn the AC on so cold. Turn AC off for about 1/2 hr to let evaporator ice melt.

Well, that was what I thought when it first started happening. Since my original post last year, I started running the AC to keep the duct temp at 40F. I still have the problem, but I'll try running it around 50F to see how long it takes to repeat the symptom.

I always notice the flow decrease before the temp increases. It gets to around 60F and turns humid. I turn it up to high (the speed increases on each setting) to get more air out, and the temp will drop down but never below 50F.

If the evaporator is freezing, you need more r134a.

Ahhhh, now we're getting somewhere!! The thought about low r134a crossed my mind, but I figured that since my AC can put out mid-30F for the first 45 mintes that the freon level would be OK. I've owned the car for 3 years, and I've never had the AC serviced. Might be time to visit an auto AC shop for a checkup.

Thanks for the input!

Update.......

My AC system was checked today. System has no leaks but was about 4oz low. Took an extended drive and issue repeated itself. It really feels as if ambient air is being mixed with the cooled air b/c the temp never rises above 60F.

Through various searches, I've read about a temp sensor that can cause the compressor to shut off, but I'm wondering if there any doors under the dash, vacuum or electric, that could cause this decrease in ariflow? Like Fedxr stated, you can hear the fan blowing at all speeds, but the output at the dash vents is a fraction of what it was when the system is first turned on.

Dealer said..

...blower motor is hot. So I replaced the blower motor, visually checked resistor(looked good) and still same problem. I haven't had 134 level checked but that will be my next step. The system kept us "cool" enough but I can def. tell the air is not the velocity it should be?? I may just live with it until it totally goes out, if ever.

Yeah, it seems odd that I can hear the blower motor increase at each switch position, yet the output isn't significantly higher until on setting 4. It really feels like some sort of diverter valve or door partially opens to allow the fan to blow the cold air somewhere other than out the dash vents. it is nothing like the other problems I've read on the numerous searches.

In my troubleshooting, I know:
1)The system is full and leak-free.
2)The radiator fans both come on with key "ON" and AC selected.
3)I can feel the compressor kick on when AC button is selected.
4)The fan speed increases at each switch position (even when acting up).
5)After about 45 min, airflow decreases and warms to 60F (10-15F rise).
6)If I run the system on "4", the system will sometimes cool back to 50F.
7) If I shut down and restart, the system will cool back into the 40's then repeat

Are you sure that the problem is not excess water collecting in the condensor? I have a 99.5 and water draining has been a continuing problem. After my AC runs for an hour or so, it begins to warm also. After I let it sit for 10-15 minutes it drains out a petty good puddle of water and then it works fine again. I have not figured out a way to get it to drain out the condensate better. Any ideas? This sure soounds like the same problem you guys are having. I actually put on a new compressor and dryer a couple of years ago so I know the system is sound.

water drain

It does seem that there is quite a bit of water puddled under the car after we park. I just thought maybe VW's puddled alot. THis is my wife's car so I didn't really pay attention to the puddling until we started having this issue. Maybe it is a result of running the A/C on 4 and at the coolest temp for a long period of time. This might not be abnormal drainage for a system that runs continuous on the highest/coldest setting possible for an extended amount of time? Hmmm...I really don't want to take apart the dash

stevebanks said:

Are you sure that the problem is not excess water collecting in the condensor? I have a 99.5 and water draining has been a continuing problem. After my AC runs for an hour or so, it begins to warm also. After I let it sit for 10-15 minutes it drains out a petty good puddle of water and then it works fine again. I have not figured out a way to get it to drain out the condensate better. Any ideas? This sure soounds like the same problem you guys are having. I actually put on a new compressor and dryer a couple of years ago so I know the system is sound.

Click to expand...

As an earler poster suggested, your symptoms line up with a freeze thaw cycle ....

Have you changed your pollen filter?

When this first started, freezing up seemed likely, as that would explain the restriction of airflow. I've been running my AC with the temp knob turned to about the 8 o'clock position. This usually gives me 45F at the vent, but the problem still occurs after extended use.

Under the dash is the evaporator, correct?

Regardless, is it possibe that the years of use have trapped dirt, debris, and bacteria in this component (which also makes the system smell musty)? Rather than evaporate the moisture, this gunk might be trapping it and the moisture then freezes up. Maybe nothing is really wrong with our systems other than needing a good cleaning under the dash. Question is, can one get under the dash to check (and clean out) this component?

Filter was changed...
What I mean is that I don't want to have to take the dash apart in trying to diagnose this problem. I have thought about taking a scope of some sort or trying to snake it down the ducts and see if there isn't a door/flapper valve of some sort that maybe is closing when it shouldn't. But it isn't closing all the way if that is the issue cause I'm still getting air...Well I'm glad to hear I'm not the only one thinking about this...not glad yall have the same problem...

if it keep freezing a few things may be wrong. Your drain is plugged and the escess water is freezing up. The low side pressure switch is faulty and not shutting down the compressor. The highside switch is faulty also not cycling compressor. The expansion valve coudl also be bad. These are what need to be checked. Im betting the compresso risnt cycling off like it should and thats why your gettin the freeze up condition. Forgot to mention that you might also have moisture in the system from an amateur doing an a/c recharge. Moisture will most certianly freeze up inside the lines.

Wow! Thx man for all the possibilities. I will get to that checklist.

Well, it's a less-than-comfy 100F today. Went for a drive during lunch. AC did its normal thing; cooled down to 45F then went back up to the 60s about half-hour later. Got back to work and popped the hood: both fans turning, drain plug draining, AC on. Got back inside, guage reading 65F. I turned off the compressor, then immediately turned it back on. The system dropped back down to 40-45F.

Maybe that low side pressure switch like Antsrcool mentioned; maybe someting else. Anyway, don't want to hijack, but it appears that Fedxr and many others have the same problem. Hopefully, my troubleshooting/experimentation will help somewhat.

Could this problem have anything to do with this temp sensor? I have a problem very similar to this. And I doubt my evaporator is freezing up. When I unplug this sensor the compressor's clutch disengages. I've had zero help with my problem so far so I thought I'd try someone elses thread that has people in it who know what they are talking about. Like does anyone know the offical name of this? or the part number? I think someone earlier in this thread mentioned this sensor but nobody carried the topic further.

this is what I believe to be the A/C thermal cut out switch (F163), which is missing on my car, the elbow is there, no space for a connector on the elbow, but the wiring/connector is there, just looking for somewhere to go. My A/C BTW worked last week with this not plugged in to anything. Anyone have a value to test the high pressure switch with? Nothing in my bentley...

egibbys said:

Could this problem have anything to do with this temp sensor? I have a problem very similar to this. And I doubt my evaporator is freezing up. When I unplug this sensor the compressor's clutch disengages. I've had zero help with my problem so far so I thought I'd try someone elses thread that has people in it who know what they are talking about. Like does anyone know the offical name of this? or the part number? I think someone earlier in this thread mentioned this sensor but nobody carried the topic further.

Click to expand...

Well after two summers of struggling with this same issue, I decided to finally do a search on the forums. Its good to see folks trying to find out what the problem could be. I have zero AC experience so I am hoping someone could provide a how to on the subject if it is fixable without having to take it in to an AC shop. Will be following closely...

What exactly does the F163 do? My car is a 99.5 and does have this switch.

Out of boredom last night, I did a google search and found quite a few VW A/C topics. A few were narrowed down to electrical problems, so here are a few interesting posts I found at VWVortex that are similar to our issue:

http://forums.vwvortex.com/zerothread?id=1175124 (TReg Forum)

http://forums.vwvortex.com/zerothread?id=3903564 (Golf/Jetta MkV forum)

http://forums.vwvortex.com/zerothread?id=3469601 (Sensor for Evaporator Outlet Temperature (G263)) - do Mk4's have this or something similar?

If anyone knows if any of these might apply to our AC systems, please post.

As a precaution, I did replace my cabin air filter today; it was filthy and hadn't been replaced in 2 years. One of those posts mentioned that a low-flow from a restricted cabin filter could cause the evap to freeze. I dunno, but mine needed changing badly, so maybe there'll be some improvement.

FWIW
My air filters are relatively new. Still have the A/C problem.

I found last night that my A/c clutch is getting 5VDC when the A/C is on, and my fans are working properly. Now that I see that the clutch is getting voltage, I was wondering if anyone knows if 5V is the proper voltage for it to get. Many sensors in a car work on 5V, I'm just not sure on the A/C clutch. Any Ideas?

Thanks,
Joe

The a/c clutch is not running with 5 volts is it? I am having a/c issues as well and mine has 8.6 volts and it is not enough. If you use 12 volts does it turn? Use jumper wires off of the battery to check this, it took 12 volts to get my a/c clutch turning.

The "low side switch" on a 97' is below the dryer on the pass side just under the nose of the car. They call it a tri switch or somthing simmilar.
It has two sets of contacts. One set allows the compressor to run presumably the low freon, or pressure controll to cycle the compressor. (IIRC it is a cycling system based on low side pressure to cycle the compressor). if it ain't cycling somthing is wrong on my system. The other contact runs the fans. It is unclear why it uses pressure to run the fans, but I know the low side pressure increases as the AC is moving more heat out of the car, or ambiant temp is higher. This pressure switch can be replaced by simply unpluging the electrical, and unscrewing it from the dryer . It has a tire style valve to prevent a lot of leakage. If you have some oil inside the electrical connector, it is leaking thru the sensor and bad. If your compressor isn't (compressing sufficently) the fans wont run and the compressor will run continiously. My compressor died, and I have the compressor turning and fans not running symptiom... extremly poor preformance regardless of charge, even if jumpered to run the fans continiously...

The third function of the switch is unclear, but perhaps the low freon compressor cutoff is a third function thru some logic, or one common cotact I missed. I beleive the AC is ECU controled..
Hope this is reasonably clear.. any input apriciated..
I just ordered a new compressor..

CB

Any differences between the mk3 and mk4 systems? I guess a better question would be: what sensors are on the Mk4 system that control the AC compressor's operation? The evaporator freezing seems to be common on many different VW models, so a faulty sensor seems to be a likely cause.

I can't believe how many posts are out there describing this problem while so few responses exist with a solution.

I second that Bayou...in fact it was some time before anyone even replied to my post. I kissed this post goodbye a long time ago. Don't worry about hijacking, this is exactly what the forums are for. Someone is bound to come up with a solution.

Did anybody ever come up with the cause?

I need to buy a Bentley manual. In the meantime, anyone with one of these VW bibles wanna take a peek to see what sensors are on the system. So far, I only know about: high pressure switch, low pressure switch, and that F163 switch above that doesn't seem to be on all cars.

I think if we can get a list of the various sensors on the AC system, and their purpose, then we'll have a good starting point for narrowing down the problem.