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TDI 101 Got a simple/basic TDI question? Are you a newbie (new to the forums). Feel free to post your question here.

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Old May 25th, 2008, 05:50   #1
fitforever
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Default Air Conditioning - Does Not Work When Stopped

My 04 Passat TDI is running great with only 75K miles but now I have a weird AC problem. For the first 15 minutes of driving after starting the car the AC does not work when the car is ideling. It blows hot air. When I start driving the air gets cool and runs like normal. But when I approach a stop light at an intersection is goes warm again. After driving for 20 minutes the AC starts working normally, even at stops. I'm in Texas and it's hot now so before I give my car to VW to fix I wonder what the probelm is.
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Old May 25th, 2008, 06:06   #2
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Check to see if both fans under hood are running with AC on. If not you have a bad fan of fan control module!
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Old May 25th, 2008, 06:51   #3
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The freon is not getting cooled enough. The reason the AC works fine at speed is that there is enough air flow through the condenser to suck the heat off that the freon picked up. When the car is stopped there is not enough air flow. As mentioned, check and make sure the fans are running.

If the fans work correctly then I would take the car to a shop and have them check the amount of freon. Low freon will cause similar problems.

Freon 134A systems usualy have to be topped off more often. I usually have my car topped off every two years.
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Old May 26th, 2008, 02:32   #4
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Quote:
Originally Posted by BKmetz
Freon 134A systems usualy have to be topped off more often. I usually have my car topped off every two years.

Not good, your system has a leak and it should be found rather than just topping it off. Gone are the days of topping off your A/C every year or two.


If the air con works only when driving then one of 2 things is wrong:
1) the compressor can only move enough refrigerant when it is spinning at speeds above idle
2) there is only enough airflow over the condenser when you are moving

To test for 1, have a mechanic attach high and low side pressure gauges to the system and monitor the pressures both at idle and with the engine revved up to 2000RPM. Depending on what the gauges read this could be either low refrigerant or a bad compressor (or many other pieces of the A/C system but these are the 2 most likely for this situation)

To test for 2, check the condition of the fans when the A/C is on, that is, are both fans running, only 1, none?... high speed or low speed? Is this the same when it is working properly as when it is not? This issue could be a bad fan controller and/or bad fans
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Old May 26th, 2008, 04:06   #5
Joe_Meehan
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Quote:
Originally Posted by BKmetz
Freon 134A systems usualy have to be topped off more often. I usually have my car topped off every two years..
Certainly not my experience. I have not needed mine topped off yet and I bought it in 2002.

Other than a leak caused be a damaged line in my Diesel Rabbit back in the late 70's I have never had any car A/C need topped off or repaired. Most of my cars I have had well over 100,000 miles. and a number of years. I have never had a car for less than four years.
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Old May 26th, 2008, 06:50   #6
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Quote:
Originally Posted by Zero10
Not good, your system has a leak and it should be found rather than just topping it off. Gone are the days of topping off your A/C every year or two.
I agree.

When you have a 12 year old car, minor slow leaks happen. It's a lot cheaper to top off than start throwing a lot of money at replacing parts. For the first 5 or 6 years both my Passats had tight AC systems too. The usual weak link is the compressor. Over time it wears and the tolerances are not tight anymore. So it starts to leak. It's also the most expensive item to replace in an AC system.

There are two types of AC systems: 1. those that leak, and 2. those that will leak.

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Old May 26th, 2008, 07:01   #7
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AC systems have the habit of allowing the seals to dry out over the winter months if it isn't engaged at least once a month year round .

Many times what happens is a seal drys out allow a slight leak over the winter months . The leak wets the seal making it reseal at a lower pressure which allows the system to function while the engine is at higher rpms and the car is moving at a faster speed . But at lower speeds the refrigerant volume is too low to function .

Many times a little charge of refrigerants is all that is required to achieve full function once again .
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