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12K views 7 replies 6 participants last post by  rs141 
#1 ·
Hi
My 2008 Rabbit had the AC working fine when I bought it in September. However, when I went to turn it on last month there was nothing. The AC light came on but no cooling. I bought some refrigerant with a gauge but it was only on the low end of the charge. After reading other threads, I turned the key to on, the fan to low and the AC button pushed. Nothing happened under the hood. The radiator fans didn't start turning and the compressor didn't start to turn. Looking at the compressor and reading here it seems that the compressor is always on, variable displacement so it doesn't appear to have a clutch.
Any thoughts on where to start? On the older VW the first culprit would have been the FCM but that is different on the 2008. I am not sure where to start the debugging.

Any thoughts?

Thanks,
Brad
 
#3 ·
I didn't think the fans were supposed to kick on before the engine was running (assuming the engine is still cold). Am I missing something? Is the a/c supposed to be able to work without the engine running? Regardless, if one or both of your fans aren't running when up to operating temperature, you would probably be noticing the engine overheating and/or one of the fans being excessively loud to compensate for the other not working. That happened to me when my small fan died years ago, granted I'm in Texas so the heat here could have contributed to it being more noticeable. If I remember right the fan failure left fault codes so that shouldn't be too hard to diagnose if that's the issue.

Otherwise, if the a/c just isn't working at all even when you're driving, it could be any number of things. First, make sure your cabin air filter isn't completely clogged. Second, don't use those refrigerant bottles with gauges to add refrigerant. Refrigerant level is measured in weight, not pressure. Have someone who knows what they are doing measure the low and high pressure sides with real refrigerant gauges to help diagnose. Third, you can check for physical issues with wires, hoses, connectors, etc. I think everything else would be diagnosed through vagcom data.
 
#4 ·
I have a follow up question on this topic. I have a similar issue, my AC is intermittent, if I shut it off, turn it on, it may or may not get cool. If I'm traveling at a higher rate of speed consistently, the AC is more likely to kick in. Either way, something clearly is wrong. If I bring it to the VW dealer, can they diagnose the problem without pulling the entire dash apart?
 
#5 ·
Refrigerant level is measured in weight, not pressure.
Umm, what?


You most certainly have to know how much pressure is in the system.

Your goal isn’t to add the right number of ounces; it’s to have the correct pressure. The entire
system is based on pressure, which determines how cold it can get. Too much pressure
and it doesn't evaporate correctly. So, the more you add, the higher the pressure will
get. That's why you need a pressure gauge.

Refrigerant Under Pressure:

If you want to know why having too much refrigerant results in hot air, you have to
understand a little bit about how an air conditioner works. The R-134a refrigerant
used in car air conditioners would normally be a gas (it boils at a frigid 15 degrees
below zero). If you compress it and pressurize it enough, though, it turns into a
liquid. The compressor in your vehicle’s A/C does exactly that, so you have liquid
R-134a pumping through part of the A/C system. When that liquid reaches the
in-dash cooling unit (called an evaporator coil), it passes through a valve that
lowers the pressure. The lower pressure allows the liquid to boil and evaporate
back into a gas. It absorbs heat from the air in order to boil. With the heat
removed, the air becomes cold. If you don’t have enough refrigerant, it won’t
be able to cool the air. If you have too much, though, the pressure will be too
high for the refrigerant to boil or for the compressor to work. Which means the
system won’t cool at all, and you’ll still be left with hot air.

Sometimes people wind up with too much refrigerant because they try to add a
certain number of ounces or cans to the system without checking the pressure.
Your goal isn’t to add the right number of ounces; it’s to have the correct pressure.

What Could Possibly Go Wrong?

Understanding how the A/C system works can help you understand what causes it to sometimes not work.
If your A/C is blowing hot or lukewarm air, the most likely culprit is low refrigerant. That’s because, except
for the compressor, there aren’t really any moving parts in an A/C system; the refrigerant is the moving part.
Since it’s a closed loop, your A/C doesn’t ever "use up" refrigerant. And refrigerant can’t wear out any more
than you could wear out water or air. The only way your refrigerant can be low is if it has leaked out.

So, as long as the compressor works, a broken car A/C can usually be fixed by sealing the leak and
refilling the system with R-134a refrigerant. The easiest way to do that is by adding R-134a. If the leak
is in a metal part instead, it needs repaired. Don't use sealants from cans...

The BEST way, is to a shop, where they can evacuate the system, and based on the SPECS, add the
correct amount without using a pressure gauge, because it's only supposed to have so much in it.
Even after a complete evac and refill, they use a pressure gauge to see where it's at, then ADD more
if the pressure isn't right. If you have to add refrigerant, then there's a leak, it must be fixed.

The weight is based on an empty system, to full. For example, on a ford, right under the hood
it actually states 33 ounces or 30-38psi. This is from a completely empty system to recharge.
As a DIY'er, you can't know how many ounces your adding, so you have to go by the pressure
gauge.

AS STATED, the only way to do it right, is to have it evacuated, repaired, then the OEM ounces
added to the system, then test. No one should be adding refrigerant to their cars, it means
there is a problem that needs to be addressed.

 
#6 ·
I took the Rabbit in for service and the refrigerant pressure was correct but the A/C didn't work. It was the compressor so I had it changed out and recharged. It worked well for 1 month. No A/C again but the refrigerant pressures are correct. It seems like another compressor. Any thoughts as to why compressor would fail so quickly?
 
#7 ·
Hi My 2008 Rabbit had the AC working fine when I bought it in September. However, when I went to turn it on last month there was nothing. The AC light came on but no cooling. I bought some refrigerant with a gauge but it was only on the low end of the charge. After reading other threads, I turned the key to on, the fan to low and the AC button pushed. Nothing happened under the hood. The radiator fans didn't start turning and the compressor didn't start to turn. Looking at the compressor and reading here it seems that the compressor is always on, variable displacement so it doesn't appear to have a clutch. Any thoughts on where to start? On the older VW the first culprit would have been the FCM but that is different on the 2008. I am not sure where to start the debugging. Any thoughts? Thanks, Brad
 
#8 · (Edited)
My daughter has the same car. The AC went out. I checked the fuses on the left side dash. There at the bottom I found 3 and the 40 amp fuse was for AC. I was blown I didn't just replace it. I knew the fan may be frozen. I need to go to the right side of the car and remove the cover behind the glove box under the dash. Then I looked up the fan was there. I pull down the tab turn the fan and pull down. I removed the fan and unplug it. I checked to see if it turned. It was frozen. I need to replace it. A new one from Amazon $38. I had bought the Schematics to locate the problem. Easy fix with the right info.
 
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