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low pressure in low ambient

zepfan
zepfan Member Posts: 312
in A-C, Heat Pumps & Refrigeration
we have a 134a condensing unit, with a pumpdown cycle.The unit is good down to 20 degree outdoor temperature.The problem we are having is we are having temperatures now much colder then that, and sometimes the suction pressure does not rise high enough to make the low pressure switch.The manufacturer is developing a low ambient kit to allow the unit to operate down to 0, but it will not be available for three weeks.my questions is what can be done in the meantime to allow the suction pressure to rise high enough to make the low pressure switch? Would it be best to put heat tape on the receiver, and add false heat to the unit that way?Once the system is up, and running it works great and cools the product. Thanks to all.

Comments

  • pecmsg
    pecmsg Member Posts: 1,959
    Best is to order the equipment with the factory Low Ambient Kit.
    Order the after-market kit for that model.
  • Techman
    Techman Member Posts: 2,144
    edited February 2015
    Use an adjustable LP control and set it down below 6psi cut-in and a 5 differential or so,you might have to go below 0 psig(heaven forbid), using heat tape on the receiver usually require's insulating the receiver as well. and also a crankcase heater is needed. What is the application? What type of head pressure control is there?
  • zepfan
    zepfan Member Posts: 312
    the compressor has a crankcase heater,and the hp control is an adjustable fan cycling switch 200 in/125 out.Yes I also think an adjustable low pressure control may be the only answer.The lp switch that is on there now is a non adjustable 5 out/20 cut in + or - 5 psi. once the switch makes the low side stays up, and the unit runs fine.During the extreme cold below 20 degrees when the liquid line solenoid closes the low side sometimes hovers around 23-24 psi, and the switch doesn't close,therefore the compressor stays off.The application is a wine cellar.Thanks for the response
  • Techman
    Techman Member Posts: 2,144
    That hp cut-in of 200psi is higher than it is supposed to be by 20psi. And the hp cut-out can go down to 115psi if you want
  • Empire_2
    Empire_2 Member Posts: 2,343
    Some lo ambient kits will bypass the lo pressure control for a set amount of time until head builds and suction pressure comes up to working load conditions. An adjustable TDR delay on break will get you started until factory kit can be ordered.



    MPT...
  • Techman
    Techman Member Posts: 2,144
    What should the pressurers be?
  • Techman
    Techman Member Posts: 2,144
    OK now this is way it is, on a "regular SEER" AC and damn near every refrigeration system . With EVERYTHING in an ACR system being proper the following holds true. On a 70* day the head TEMP is equal to 95* condensing temp and on a 95* day the cond TEMP is equal to 125*. All of the different freons will have different pressurers,now with 10 different freons that is 20 different pressurers to memorize, and what do you do for an 82 1/2* day? This is 95*cond temp or 113.5 psig for r134a and 125* cond temp is equal to 184psig for r134a.
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