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  1. #1
    i don't know much about them, so how does a low ambient control work and in what applications would you use one?

  2. #2
    Join Date
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    It controls head pressure in low outdoor air temperatures. Mainly used on commercial equipment. A prime example would be cooling a server room with an air cooled condenser and DX evap. Fan cycling, Fan speed contol, hot gas bypass are all means of controlling the head pressure. Basically it artifically increases the head pressure to maintain a high enough high side pressure to keep the low pressure side from getting too low and causing a freeze up on the evaporator. We've also used them alot in commercial buildings where due to the solar or interior load the cooling equipment (air cooled) needs to run when it is less than 60 degrees outside.
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  3. #3
    Join Date
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    Low ambient can also include a timed bypass upon startup of the low pressure control until the head/suction pressure build enough to not keep short cycling on the LPC.
    Jogas

  4. #4
    Join Date
    Jul 2001
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    Can also be as simple as a LOW TEMP LOCK OUT thermostat

  5. #5
    Join Date
    May 2002
    Location
    Madison, Wisconsin
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    429
    Yet another very reliable low-ambient control method is a heated refrigerant reciever. Not exactly energy efficient, but succeeds when other methods fail. It's not generally used by itself, but along with other low ambient control methods such as fan speed control.

    The very first low-ambient control I ever saw was a foot-long bellows, connected to the high side, that operated a damper in the condensing unit's air stream. The damper had an end switch, that enabled a head-pressure-controlled fan. That was in the 70's, and the unit was about 20 years old at the time. I saw it operating flawlessly on a -20* day. Wish I could remember who made it.
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  6. #6
    Join Date
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    Originally posted by fixitman
    Yet another very reliable low-ambient control method is a heated refrigerant reciever. Not exactly energy efficient, but succeeds when other methods fail. It's not generally used by itself, but along with other low ambient control methods such as fan speed control.

    The very first low-ambient control I ever saw was a foot-long bellows, connected to the high side, that operated a damper in the condensing unit's air stream. The damper had an end switch, that enabled a head-pressure-controlled fan. That was in the 70's, and the unit was about 20 years old at the time. I saw it operating flawlessly on a -20* day. Wish I could remember who made it.
    That's a Robertshaw damper operator. I just disconnected 2 from a '70's trane condensing unit(dampers were shot). The problem with those were the damper shaft seal would leak and you'd lose refrigerant. We opted to add a VFD for condensor fan/head pressure control. It's working great with the Alco Hot Gas Bypass Valve.
    Jogas

  7. #7
    Join Date
    May 2002
    Location
    Madison, Wisconsin
    Posts
    429
    Originally posted by jogas
    Originally posted by fixitman
    The very first low-ambient control I ever saw was a foot-long bellows, connected to the high side, that operated a damper in the condensing unit's air stream. ...
    That's a Robertshaw damper operator. I just disconnected 2 from a '70's trane condensing unit(dampers were shot). The problem with those were the damper shaft seal would leak and you'd lose refrigerant. We opted to add a VFD for condensor fan/head pressure control. It's working great with the Alco Hot Gas Bypass Valve.
    Jogas
    Same idea, but you had a different animal there. There were no shaft seals on this gadget. It was a bellows much like the type thqat's in a refrigeration pressure control, but very long. It was contained within a tube (to keep it from buckling when it pushed, I assume) and there was a pushrod that ran through a guide in the end of the tube. but the end of the bellows was visible through the pushrod end.
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  8. #8
    Join Date
    Jan 2012
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    WEST COLUMBIA S.C.
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    275
    Medium temp.cooler shuts off when outside ambient is low .What would be the proper cut in cut out on a R22 system maintaining a box temperature of 40 degrees

  9. #9
    Join Date
    Jun 2006
    Posts
    68
    Make sure the cut in pressure saturated suction temperature is below the coldest ambient temperature. Around here on R22 I use 8lbs CI and 2lbs CO. This will keep it running when it is -20F.

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