Headmaster ??
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Thread: Headmaster ??

  1. #1
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    Sep 2010
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    Headmaster ??

    I understand in low ambient temps the valve will stack liquid in the condenser n bypass hot gas into the receiver keeping the head pressure up, here is my question. If the unit is low on charge usually your hi n low read low but with a head master I'm thinking it's going to try it's best to keep the head pressure to its valve design pressure ???

  2. #2
    Join Date
    Oct 2012
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    Yes, headmaster will try to keep its design pressure. If you are really low on charge it will feed hot gas right to the expansion valve.

  3. #3
    Yup...that's the story...Low side will be low because it isn't getting 100% liquid to the metering device...Hi side will be low or somewhat low depending on how much undercharged your system is. The key to T/S a headmaster type arrangement is to feel the liquid line downstream of the headmaster valve.....if it is feeding liquid from the condenser the temp of the line will be ambient (OAT)...when the bypass happens you will feel the liquid line downstream of the HM valve feeding the receiver turn warm.....then when it shifts to feed liquid it will go cold...back and forth between the two temps....if the thing is "stabilized" (feeding both liquid and hot gas bypass) it will be warm...something less than hot gas temp and something more than OAT.....I've only seen a stabilized HM valve on a rare occasion.

    To answer your question directly....until the high side hits the bypass setting of the headmaster it isn't going to bypass anything to the receiver...your liquid line from the headmaster valve will always be warm or hot...showing superheat temp above the condensing saturation point.

    Watch yourself on charging that system....if the receiver isn't sized for a headmaster type setup you can easily overcharge in the lower ambient time of the year and then have to remove gas when the seasons warm up.....

    Hope this helps...headmasters are often one of the great mysteries of life....do you also have condenser fans that are set up on pressure controls?

  4. #4
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    I was doing a maintenance on Friday. It was on a liebert unit. I seen it had 2 receivers the ball was only floating in 1, the other reciecers ball was sitting at the bottom. It was getting late I might be going back Monday 1/7/13 to finish the maintenance. The liquid line comming out the condenser was pretty cool. Line going int the receiver was warm the valve was bypassing I guess that could explain why the other receiver was empty due to the refrigerant was stacking in the condenser instead of in the receiver, I can't remember I had 22 degrees sub cool the exact pressures n temps I have on my note pad at home, I checked pressure n liquid temp leaving the condenser coil. Could that be the reason for my high subcool

  5. #5
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    Mississippi
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    Whats the ambient in miami? If this is a 407c unit, to check charge you got to raise head pressure to 230 psi (blank off coil) and disable hot gas bypass. Your sightglass ball should be floating on receiver thats lowest.

  6. #6
    Quote Originally Posted by anthonyac1 View Post
    I was doing a maintenance on Friday. It was on a liebert unit. I seen it had 2 receivers the ball was only floating in 1, the other reciecers ball was sitting at the bottom. It was getting late I might be going back Monday 1/7/13 to finish the maintenance. The liquid line comming out the condenser was pretty cool. Line going int the receiver was warm the valve was bypassing I guess that could explain why the other receiver was empty due to the refrigerant was stacking in the condenser instead of in the receiver,
    I can't remember I had 22 degrees sub cool the exact pressures n temps I have on my note pad at home, I checked pressure n liquid temp leaving the condenser coil. Could that be the reason for my high subcool
    Where did you check the subcooling.....between condenser and headmaster or between headmaster and receiver?

  7. #7
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    Quote Originally Posted by montana red View Post
    Where did you check the subcooling.....between condenser and headmaster or between headmaster and receiver?
    sorry i should have stated it better, i was thinking of a basic condenser. i actullay checked it on the liquid line outside of the condenser so basically that would be the liquid line leaving the receiver.

  8. #8
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    Sep 2010
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    Quote Originally Posted by socotech View Post
    Whats the ambient in miami? If this is a 407c unit, to check charge you got to raise head pressure to 230 psi (blank off coil) and disable hot gas bypass. Your sightglass ball should be floating on receiver thats lowest.
    its r22 outdoor ambient was was about 80 degrees.

  9. #9
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    Quote Originally Posted by anthonyac1 View Post
    its r22 outdoor ambient was was about 80 degrees.
    I would not expect it to bypass at 80* ambient with a proper charge. So I would say your low on charge and therefore bypassing.

  10. #10
    Quote Originally Posted by anthonyac1 View Post
    sorry i should have stated it better, i was thinking of a basic condenser. i actullay checked it on the liquid line outside of the condenser so basically that would be the liquid line leaving the receiver.
    Okay...back up the bus...if this system has a headmaster set up then that means that measuring the Liquid Line coming out of the condenser would be before the headmaster.....if you measured there then it's just going to be subcooled liquid sitting there waiting to go to the receiver through the headmaster......did you do a feel check of the liquid line leaving the receiver? If you are blowing hot gas through the receiver then the line from the headmaster to the receiver and the liquid line leaving the receiver would be about the same temp plus or minus a few....

  11. #11
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  12. #12
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    Quote Originally Posted by VTP99 View Post
    I would not expect it to bypass at 80* ambient with a proper charge. So I would say your low on charge and therefore bypassing.
    Yep. Bypassing on a properly charged unit doesn't start til it drops below 65ish ambient.
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  13. #13
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    Sep 2010
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    i appreciate all the replies ive seen the head masters but never really had to deal with refrigerant issues with them. they assigned me to this one account with a couple of liebert units not to familiar with them but want to get the experience with them. so i cant tell the office im scared lol or else they will assign it to someone else. i appreciate your feed back.

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