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  1. #27
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,826
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    Quote Originally Posted by BBeerme View Post
    Here is the easiest way to think of it. Have you ever seen a pump down system? If so, you could call that solenoid a 100% restriction. What happens to the head when a system goes into pump down? I think you'll find that it goes down. In fact, it will try to achieve a pressure relative to the ambient. Like in a refrigerant bottle.

    Regarding being over charged, the condenser would have to be very full. I sort of got the impression that the head was varying. And if so, that is a huge clue. Whatever the problem is, even an overcharged system does not make the head vary. Yes, it could be very high, but it would stay there.
    I understand that. I work on a lot of pump down systems.

    Now add a partial restriction that cant be seen. Low head. Low suction. High sh. Joe scmoe doesnt know better so he keeps adding gas until he has a 70psi suction. Restriction gets a little worse and system not performing well, now i get the call out there.

    I find low suction. High sh. High sc. And high head. Restriction with an overcharge. How do i know you may ask?

    Total charge should be 10lbs. Recover 20 or more lbs and fix restriction. Weigh back in 10lbs and all is good.

    Sent from my SM-N900V using Tapatalk

  2. #28
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    3,263
    Post Likes
    Quote Originally Posted by gravity View Post
    I understand that. I work on a lot of pump down systems.

    Now add a partial restriction that cant be seen. Low head. Low suction. High sh. Joe scmoe doesnt know better so he keeps adding gas until he has a 70psi suction. Restriction gets a little worse and system not performing well, now i get the call out there.

    I find low suction. High sh. High sc. And high head. Restriction with an overcharge. How do i know you may ask?

    Total charge should be 10lbs. Recover 20 or more lbs and fix restriction. Weigh back in 10lbs and all is good.

    Sent from my SM-N900V using Tapatalk
    Yeah, this post reminds me of a 'test' question I like ask rookies. The question goes like this: All else being normal, for example a normal install with normal duct work, and all motors working proper etc, you walk up to an A/C with low pressures. What is the first thing you do?

    The answer, of course, is to measure the subcooling. Even close to 50% of experienced techs will say to add gas. As you indicated above, if you have a high subcooling, adding gas won't help the situation.

  3. #29
    Join Date
    Jul 2012
    Posts
    1,403
    Post Likes
    I have a carrier roof package gas that had a burn out. It is restricted. I think I am going to cut it out and install a txv.

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