Last weekend we took a road trip of about 700 miles. We used the A/C on the way, worked great. Spent a day at the Steel Valley Nationals in Salem, OH, didn't need the A/C so didn't use it. When we jumped in the car for the return trip and fired up the A/C, no go. When we got home, I checked the pressures and nada. Sometime between Friday evening and Sunday morning, I lost all the refrigerant for some unknown reason. It had been working fine for several weeks before that.

Today, I tried to add some back to the system and now it won't take any juice. When I open the valve to start the flow (low side), the low side pressure jumps to 120 and NO refrigerant will leave the can and head into the system. What gives?

Oh, and I'm using R134a.

What makes you think you have no Freon in the system? 120 psi tells me you have some and odds are you are not turning the compressor when trying to charge the system. Jump the pressure switch and see if the AC compressor engages it's clutch then look at your pressures

If the system vented completely empty, I think you'll have to draw a vacuum down to pull the air out of the system before the refrigerant can go back in. I'm not an expert at all, so this may be a little off.

does the clutch engage? you are doing this, with the motor running? and the clutch is engaged while you are trying?

Sometimes you need to jump the low pressure switch to get the compressor to work and draw in the freon. Also be sure the gauges you are using actually push the shrader valve in to open the charge port.

I wouldn't try adding expensive refrigerant unless you know where it's leaking.At the very least add some dye to the refrigerant so you know where the leak is next time.

I've used this gauge set for many years so I know the valves are all good. The compressor doesn't come on (no pressure in the system) but will engage if I jump the switch.

I've looked the system over and can't find any obvious places it would be leaking so I'll need to add the refrigerant to aid in finding the leak (assuming there is one).

You're probably right about the vacuum. I'll try putting it into vacuum this weekend.

Thanks for all the feedback!

Once you have vacuum in the system(if it pulls down),do a leak down check. You should'nt lose much if any vacuum in say 5 mins or so if the the system is good,d

If you have to jump the lp switch there is nothing in the system. Big leak someplace.

I've vacuumed the system down to around 20" and left for 30 mins with almost zero loss. Still, when I try to add refrigerant, the low pressure on the gauge jumps to nearly 110psi and it'll take no refrigerant. When I force the compressor to engage, the low side pressure jumps to around 120psi and the high side goes to maybe 25psi. Still, it takes no refrigerant.

I've charged a few of these things and I've NEVER seen the low pressure that high when charging or running. Usually it's in the 45psi range when the compressor is on. Way below that and rising while refrigerant is entering the system.

I'm thinking something mechanically is wrong with the system. Anyone have any ideas?

Looks like no A/C for Carlisle this weekend...

i think you have your high side and low side manifold valves open at the same time (with both hose ends connected and open to the vehicle). Hence the reason the high side looks to read low, and the low side reads high. The high and low side are equalizing through the manifold gauge set. Its hard to know exactly without being there.

Just my two cents. Right is closed BTW

I know you said the valves on your gauges were good, but I would try another gauge set just to be for certain. Really sounds like you are pressurizing the gauges without it passing thru the schrader vavle. Also would think you should be able to pull nearly 30" of vacuum.

All fixed. I figured there had to be a blockage somewhere so I went right to the low side line. I pulled the R134 valve and there was gunk behind it, blocking the flow of refrigerant into the system. I sucked the system down good, recharged, and voila! Cold air flows.

I'm thinking there was some junk in there left over from the restoration process. That would explain the venting of the refrigerant and the gunk I found behind the valve. There was probably a blockage at some point that increased the pressure and tripped the high pressure blow off valve.

Thanks for all the input, Guys! See you at Carlisle!