On my A4 Z28, The air doesn't work. I checked the fuse in the engine compartment, and it looks fine, also the cruise works, so the fuse must work.

I switched the ABS and A/C relay and the ABS light didn't come on, but the air still didn't work.

I bought a low side pressure gauge, and it indicates 0 psi. This is with the A/C on, (Max A/C) for about 3 minutes prior. The tube was also hot, and yes this was the low side because it was the bigger diameter one. The high side was hot also, about the same in temp though.

I then noticed the A/C compressor wasn't engaging at all.

Now my questions are this:

1. Isn't there a safety switch that will not allow the compressor to engage if there is no freon in the system?

2. If there is such a swith, will it throw a code?

3. The only way to charge the system is with the A/C compressor on, correct?

So I'm at a catch 22, will I have to short the two compressor terminals, will that manually engage the clutch? And will running it with no freon for a few seconds kill the compressor?

I realize if there is no freon there is a leak, but it's hard to tell where with no dye in the system. I want to charge the system enough to have the dye come out somewhere and then I can work with it from there. Of course my hopes is that the stop leak in the freon will be good enough to plug the leak.

Thanks in advance

 

1. yes
2. no
3. ac machine or vacuum pump

manually overriding it may cause damage, especially since you don't know if theres oil in the system

 

I got a mitivac, will that supply enough vacuum? Where would I connect it, the high side?

Thanks

 

As you add refrigerant, the pressure will increase to the point that the low pressure switch will close and allow the compressor to cycle.
As the compressor cycles, it will take the refrigerant and fully charge.
It needs to be monitored for High and Low side pressures to determine the correct charge amount.
You probably have a leak somewhere that caused the original depletion. You really ought to fix that first.
You need a vacuum pump (continuous vacuum, not momentary like a Mitivac) to evacuate the system to remove moisture prior to recharging. It's not usually necessary unless the system has been apart for some reason.

Good luck!

 

Nice info, neighbor.

I wish I knew that last week when I tried to recharge my refrigerant after I did a cam change. After spending $50 on refrigerant cans and a cheap install kit at the AutoZone in F-V and getting nowhere. I finally gave up and took it to a local shop. I'm A/C ignorant

 

Cool, thanks Tommy!