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Hi Side Pressure at 400

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  • Hi Side Pressure at 400

    I'm working a 2008 Saturn Vue. When I started, it had negative Low Side pressure, as in about 25 negative. Similar to when the vacuum pump is evacuating. I Googled the symptom and my research indicates a block on the suction side. The most common culprit being a stuck expansion valve. I know they seldom fail but I replaced it. I added one oz of PAG, evacuated the system and charged with 20.2oz of R134. Low side reading was 32. Hi read 205. Ambient temperature was 92. System worked great! Analog thermometer read 34F. Unlikely it's really that cold but cold nonetheless.

    Two days later, it doesn't cool. The system is cycling on and off. I'm thinking I have a leak and thus a low charge even through the system held vacuum overnight. A bad Schrader valve won't show with the gauges connected. I'm thinking the Low Side Schrader valve I replaced while changing the expansion valve is leaking. I connect the gauges and get Low Side 55 and High Side over 300 and climbing. Ambient temp is 92. I concluded the cycling is due to the High Side switch engaging at 400 so it's not a low charge. There's blockage on the High Side.

    I sprayed the condenser with water. It's a rather large condenser. I was able to find that spraying the top right quadrant lowered the High Side pressure to 270. I'm concluding I have a block in the condenser and likely need to replace it. It's a parallel flow. I've not had great success blowing out a parallel flow since the compressed air can take more than one path through.

    Thoughts before I order a new condenser? Thanks for any help.

  • #2
    It seams like you have contaminates though out the system. Tx valves don't "open or close" they are always a restriction, sometime a larger one and some times less of one, in otherwords they always pass some refrigerant, how much depends on the heat load. So if replacing the Tx valve helped for a little while, it was plugged to begin with.
    Where and what is causing the plug? It could be drier material, or it could be metal from the compressor. Until you get to the source you could keep replacing parts and the junk can keep plugging new parts.
    I suggest flushing into a container where you can see what debris is in the system, and go from there. You could replace the condenser and Tx valve again and still plug the new ones unless you get to the bottom of the problem.
    Tx valve systems don't cycle on and off if it has a low charge, that is something orifice tube systems do. I think you are correct that the you are hitting the high limit switch when the high side reaches 400 psi, it shuts off the compressor and the pressure drops, compressor comes back on and cycle repeats.
    If you still have the old Tx valve see if you can see debris clogging it, and what that debris is, is it metal? drier beads? or plastic? That will give you an indication of where to look. You need it clean the whole system of the junk or you'll find yourself right back where you started.

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    • #3
      Originally posted by Cornbinder89 View Post
      If you still have the old Tx valve see if you can see debris clogging it, and what that debris is, is it metal? drier beads? or plastic? That will give you an indication of where to look. You need it clean the whole system of the junk or you'll find yourself right back where you started.
      There's no debris. The old expansion valve looks brand new with a little oil on it from the removal.

      The Low Side Schrader valve came apart when I tried to replace it. I removed the hose from the condenser and blew air through it to make sure I had all the pieces out. It was already removed on the expansion valve end. Pretty sure I got it all out (pic below). If not, any debris would flow toward the expansion valve and not the condenser. This car has the drier built onto the condenser. Can't replace one without the other.

      https://www.flickr.com/photos/234393...57715265295362

      Thinking of the refrigerant flow, if I have a clog at the top right quadrant of the condenser, which is where the Low Side hose connects wouldn't the debris have to come from the compressor into the drier? I wouldn't think the condenser itself would create debris since it's just tubes passing refrigerant and oil. I wouldn't think debris would go from the evaporator through the expansion valve and through the compressor into the condenser. That would leave the compressor and drier, as you have suggested. I blew through the evaporator when the expansion valve was removed. No blockage there.

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      • #4
        All I'm saying is if you don't get to the source of the problem it will continue to cause problems in the system. It is your eyes on the system, you have to make the call, but if you don't get to the source, you could plug a new condenser or Tx valve all over again.
        It is a closed system and every recirculates though out the whole system, so any debris that makes it past one item can be stuck at the next. Parallel flow condensers have small passages to maximize surface area, so plug easily, I agree you need to replace, but if you haven't eliminate the source of the plugging, it could plug again. How many times are you willing to replace the condenser as a filter?

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