A/C keeps freezing up! Why?

Hey folks,

Does anybody have any suggestions as to why my A/C freezes up after only 10 or 15 minutes of operation? I put a complete new system on it 4 years ago and had it charged with R12. The system blows cool when you first turn it on, but after only about 10-20 minutes, the air temp starts to increase and it is just barely cooler than the ambient are temp. I have seen chunks of ice fall off of the bottom of the evaporator the size of hot dog buns after the car sits following a long run with the A/C on. Once it thaws, the air blows pretty cool for a little while, then not so cool again. Can anybody give me an idea of what could be the problem? Thanks.

Have you checked for leaks? It could be low on Freon.

My guess is that somebody has by-passed your low pressure shutoff switch or it has failed closed (unusual). If you run the compressor all the time, the pressure will go low and the temperature will go low and freeze the line up. Make sure that you have a low pressure switch either in the line or on the accumulator. It is common practice to bypass this switch when charging the system to make it charge faster. Be sure the guy who charged it didn't forget to remove his jumper wire.

You mean to tell me somebody has a vette with A.C. that actually works ? I thought they just added all that extra stuff to fill up the engine compartment !

Yes...I know exactly what it is and how to fix. My 78 did exactly the same thing...blow cold 45 minutes...then blow hot. Turn it off to defrost for about thirty minutes...turn it on and it blew cold again. Once I replaced this valve..it blew cold all the way to Hershey and back (1500 miles round trip)!

The vette guys call it an evaporator valve while the GM service guys call it an orifice valve or something like that. It inserts into the evaporator inlet tube assembly where it enters the evaporator core box (at the bottom). If you're looking at the assembly...you'll see where it unscrews about six inches from the box opening. The valve inserts into that tube...it's a bitch to remove.

The valve cost me about $4.00 but the service to replace and freon cost me $212.00!

Hope this helps.