Tony;The problem with replacing the Expansion Valve is that you probably are not curing a problem.The Compressor squeezes the liquid into a gas, making it very cold.That's why the line from the Compressor is cold and usually sweating.The Expansion Valve's job is to reduce the gas to a liquid, via a small orifice.As the liquid goes thru the evaporator, it absorbs heat and turns back into a gas,then to the Condenser, where it sheds a lot of the heat, back to the Compressor, and so on.That's why going into the Evaporator the line is cold and coming out it is hot.If there is moisture in the system it will form a ice ball in the orifice and block the system.Later it will melt and operate for a while, until it clogs again.Key here is proper evacuation. Even that is problematical if the Receiver-dryer is loaded with moisture, it's job.If you haven't replaced the Receiver-dryer, do it while you have the system down this time.There could be blockage or excessive moisture there.Be sure to add any needed A/C oil, the new Receiver-dryer will require some.You also mentioned blowing out the Evaporator, high pressure air going into here is a bad thing.Air/moisture can be in lots of places inside here and not be removed with a light Evacuation.I would suggest you have it Evacuated for at least several hours to be sure it is fully purged.You want near 25" of vacuum, won't get there, but closer the better.Then let it sit overnight and see what the Vacuum is in the morning, before charging.Extra work, but with the constant problem you have, might as well overdo and be sure.God luck, Rayp.s.: we're sending our heat wave to you, enjoy...On Sat, Jul 9, 2016 at 8:00 AM, Tony Rinaldi awrdoc@xxxxxxxxx [Chrysler300] <Chrysler300-noreply@xxxxxxxxxxxxxxx> wrote:My system is a 1962 installed into my 1960 300-F.A mechanic tried to convert to 134A without taking the EPR valve out of the compressor. It worked great but would freeze up the evaporator and stop working.Sent everything to Classic Air for rebuild and conversion. Their temperature switch makes and breaks power to the compressor blue wire if there is a freeze up. This replaces the function of the EPR pressure valve to cycle the compressor.The evaporator is open and was blown out with compressed air.System was charged and was not cold.Classic Air said it was a bad expansion valve. Replaced it and no difference.They said to charge the system with 134A at 80% of normal pressure. So they went down to 2.5 from 3 lbs.Problem is that the filter housing on the top of the condenser gets cold but the line does not get cold where it enters the evaporator.They put 4 lbs. in and I got 59 ° at the vents on the highway.Pull off to the side of the road, with engine running, to see it working well and the cooling stops. Nothing frosting up.Go back on the road and the cooling does not come back.Waiting for another expansion valve and on/off switch to be delivered.Will be replacing both once they come in.Any insight about where we are now?Thank you, in advance, for any help or suggestions.Tony
--Ray Jones. Y'all come on down an see us. Ya hear?