Re: ac questin

Posted by NCWayne on July 09, 2013 at 20:37:01 from (98.21.228.82):

In Reply to: ac questin posted by tbish on July 09, 2013 at 18:02:30:

I've had systems do similar in the past. There can be several different causes. One of the most uncommon ones I ran into was a line that had been made up WAY WAY too long that had been coiled up and zip tied in place. Thing is when it was zip tied it was also kinked to the point it was nearly collapsed.

Now on that same system when I first started on it my thinking was a stuck expansion valve. With that problem the compressor is pumping the refrigerant to the high side faster than the expansion valve can meter it through which results in higher than normal high side pressures and lower than normal low side pressures. Unfortunately changing it didn't solve the problem which caused me to begin looking further to find the kinked line. Bear in mind my customer had already spent nearly $3000 at the dealer to get the system operating, and the line I foudn kinked was a bran new line so I was about to pull my hair out before I found the problem with the line.

That all said, a restriction, of some type, between the high and low side is the only thing that's going to cause the problem your seeing. I say that because your high side pressure, in this case, is up in the range where it should be (at least in every 134A system I've worked on and read about). That being the case not having enough refrigerant in the system really isn't likely to cause the problem in an expansion valve system as the valve is going to meter refrigerant relative to the temp of the cooling evaporator core regardless of how much is in the system. In other words no refrigerant means the coil wouldn't get cold, which would cause the valve to shut, so it should be staying wide open. Because of that the pressure on the high side would typically be lower than normal just like the low side pressure.

Like another post suggested it could also be a problem with the reciever/drier stopped up, but you say you've changed that already so that shouldn't be an issue. Along that line of thinking could a plug, etc possbly have been left in/pushed into the port on one of the new parts vs being removed?

Beyond that I wish I knew what else to tell you to look for, but in the twelve years or so I've been working on mobile A/C systems the things I've talked about so far are all that I have been unlucky enough to run into. Good luck.

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