When I hook up the vaccum pump to my ac system on my 92 civic, open the valves, and turn on the vaccum pump, the pressure instantly goes down to -30hg. When i close the valves and turn off the pump the pressure slowly decreases to about 15 to 20 (this is after 10 minutes of pulling)

My question is: If the system is empty, and both high and low side are unobstructed, how it is possibly that it's pulling -30hg so fast? Shouldn't it take like an hour to build up to this pressure slowly?

 

How long have you owned the car? Is it possible that a previous owner recovered the refrigerant and evacuated the system without recharging it?

 

sorry, I failed to mention that I swapped engines and the system is empty.

This is why I feel it shouldn't build up pressure so quickly (within 20 seconds)

 

so I checked the valves and the low side r134a conversion tip had melted plastic at the bottom, so that was part of why the pressure was building up so fast.

I took that off and connected directly to the old style r12 connector and it goes up slower...

but it still reaches -30 in about 45 seconds.

Everything I've read seems to say it will take At LEAST 30 minutes to reach this for the entire system. How is this possible that mine is doing this? The system HAD to be empty when I swapped engines. I also poured all the oil out of the compressor.

I'm also double checking there's a vacuum on the system by pressing the valve pin in after I disconnect, Just to be sure, and yes, there is one, but I don't know how far in the system it's extending.

 

Sounds like you have a blockage somewhere, try pulling the vacuum from the high pressure side connection and see if it takes longer, place the cap back on the low side or it may suck air in.

Common blockage areas are the dryer and evaporator valve.

 

where are those two located?
Also should it indeed take 30 minutes to pulla vacuum?


I know I sound car ignorant but I promise I'm quite experienced, just new to troubleshooting a/c systems. Last time I did this was a long time ago and there were no problems.

 

bump, I need some advice here.

When i put my fingers over the two vacuum lines attatched to the manifold which is attatched to the vacuum pump. The pressure again rockets to neg 30 inHg. Is this vacuum pump shot?

 

The compressor was previously disconnected to do an engine swap.

Everythign is back to normal, but a vacuum pulled on the system (down to -30inhg in about 30 seconds and held there for 30 minutes) drops back to zero in about 2 minutes after i close off the manifold gauge valves.

Any idea where to start checking for this leak?

 

A lot of times it's where the line(s) connect to the compressor. Easiest way to find link is with dye and an ultraviolet light, they should have a kit at the parts store.

Shout out to the Knoxville boys. Used to live there, graduated from Oak Ridge.

 

hey hey! My dad works in oak ridge, I moved over from utk to finish school at mtsu.

Wouldnt' testing with dye require pressurizing the system with refrigerant? I'm doing the opposite. Trying to get it to hold a vacuum with the pump before i put refrigerant in it.

 

so i replaced both seals for the tubes on the compressor. but here's the kicker:

Ya know the two tubes under the air box?
the larger one goes from the Compressor Low Side <--to-> the Evaporator/Blower,
the smaller one goes from Evaporator/Blower <--to--> Condenser,


Well, when i disconnect the small line, hold my fingers over both holes, pull a vacuum, tighten tighten the gauges. it holds a vacuum just fine.

When I reconnect the tube and do the same. The vacuum drops away.

There's no seal on this tube, so i put one there, same problem.

 

well, i double checked. And I tried a seal plus forcing these two tubes together by hand. no luck.

I also tried using a peice of duct tape on each instead of my finger.
Result: System holds a vacuum.

I'm completely confounded, however i'm starting to thing this is not the proper forum to be asking ac questions in.