AC Vacuum Pump

[dpom]

I am doing my first AC repair on my 94 XLT. I hooked up the gauges and there was no pressure in the system. I attempted to pull a vacuum and the gauge only went to about 19 in Hg. After closing the thumb valve the pressure stayed there for 10 minutes. I wasn't totally convince the vacuum pump is working the way it should, so I hooked the pump directly to the gauges and it pulled to 19 in Hg.

The pump works off of my air compressor at 75 psi, it should pull 29.9 in Hg. Is there something wrong with this pump? I don't hear any hissing. Should I buy/rent an electric one?

Thanks, Dave

 

[BrooklynBay]

Check the CFM rating of your compressor, and compare it to the minimum CFM rating of your pump. You might have enough PSI, but not enough CFM.

 

[dpom]

The vacuum pump instructions say a constant source of 75 psi is required and the pump will consume 4.2 scfm and will pull a vacuum of 29.7 in at sea level.

The comressor says it does
6.6 scfm at 40 psi and
5.8 scfm at 90 psi

I will try raising the psi and see what happens.

 

[dpom]

Cranked up the psi and it worked, thanks.

No whats the deal with the pressure staying at 19 in Hg after i disconnected the pump? Is it possible that the leak is so small it wouldn't cause air to come in it? I mean there has to be a leak since the system wasn't charged at all right?

I have a new accumulator but I don't want to put that on until I fix the leak right? How do I add the UV dye without replacing the accumulator?

Thanks, Dave

 

[Glacier991]

My suggestion is that you pull a vacuum as best your pump can and let it sit overnight. If it stays the leak may have been some odd transient. BUT.... evacuation is not the best way to find a leak. You are only testing at atmospheric pressure.

The best way to find a leak is to put some refrigerant in the system... doesn't have to be much, the pressures will be 75 PSI or higher with a partial can in the system.... and either use a sniffer, or a black light.

Look for leaks at any place there is an O ring seal, at the compressor connections, and at the front compressor seal (hard to visualize with black light due to the pulley.) Also check out the valves, they tend to leak too... often producing a transient that seems to disappear after they have been opened and closed.

I'd suggest you put a can of dyed 134 in it and look that way first. Keep us posted.