AC blows hot air, Compressor engaged even with ac turned off

[Velox]

Hi,

your opinions on this one.

AC blows ambient temp air.
High pressure on low point. (bad compressor?)
Compressor is ALWAYS engaged even with AC turned off

What to eliminate as probable causes before replacing compressor?

[Audibot]

The a/c compressor in the B7 is "always" on--yes. It does not have a traditional clutch like most compressors; rather, it has a swash plate inside. So when the the compressor is not on, the swash plate is not engaged. However, when you turn on the a/c, a solenoid kicks in and moves the plate (think of it now 45 degrees to the pulley), which in turn drives the pistons in the compressor. I replaced mine about a year and a half ago.

Also, the Sanden compressors, from what I understand, suck. Go Denso.

First thing to check is the refrigerant pressure switch (G65; located on the driver's side of the condenser, at least for LHD cars). You say "high pressure on low point"--have you connected gauges up to the low and high pressure sides? You will need VCDS/VAGCOM to tell you if it's truly the sensor that is bad. You may be low on refrigerant, so the computer will not engage the compressor. However, if it does wind up to be the compressor is bad in the end, I have one I could sell you.

Picture below may help with the compressor description:

[Velox]

Aaaah ok, that explains a lot, very helpful, will definitely get back to you when compressor is needed.

[dalmation53]

My car had no a/c when i bought it 2 months ago which i found out 2 days ago. It was stuck on econ. So today i put in 500grams basically 1 can and a half and the a/c works now. Cheapest way to find out is buy 2 cans are like $10 at walmart and connect the guage to read. If is on red then you are low on R134a

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[Beastopher]

From what I understand, you have to be VERY careful when using these Walmart coolant cans. The gauges are "unreliable' at best, and if you overfill or over pressure your system you could cause more damage than just having a low coolant/oil level. Food for thought.

[Audibot]

That's why I asked OP if he had checked via manifold gauges. If you want a relatively inexpensive set of decent gauges, Harbor Freight is probably the way to go. Overcharging it result in the same as undercharging it. Furthermore, if you just willy-nilly add cans of R134a in there, you may be doing more harm as well. Most of those cans have compressor oil and/or some kind of sealant, which really mucks things up. Too much oil will be detrimental to the system.

If the pressure checks out, I would suspect the pressure switch on the condenser.

[Brillo]

It's easy to overcharge with the do-it-yourself systems from Wal-Mart, Advanced, Auto Zone, etc. Obviously, it's best to leave AC to the experts, and usually not that expensive for a recharge. Usually, the lubricating oil can then be done correctly too. In a pinch, the old rule-of-thumb was to fill just until the exit side of the evaporator coil (low pressure side) just starts to get cool to the touch with the system on full blast, no more. Feel the pipe as close to the evaporator coil as possible. Then get it checked soon thereafter.