Original message
| tav1017
 |  "WALK IN FREEZER"
, posted Wed 19 Apr 21:24  
Hello,
Newbie to commerical work, why and how are solenoid valves in conjuction with defrost timers. Unit cutting out on low pressure and found timer stuck in defrost, hence closing sol. valve.Manually turned timer out of defrost and solenoid valve kick on which would have opened the valve. Hope I explained this enough. Thanks for any answers
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Replies:
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| kilowatt
| "Re(1):WALK IN FREEZER" , posted Tue 20 Jun 00:37
the best way (for me ) is to understand that the real controll for the compressor to cut-off or on is thru the low pressure controll, whice is wired thru one leg of the compressor or thru the controll coil of a contactor or motor starter. the second component is the cabniet t'stat whice is wired in series to one leg of the pump-down solenoid that, when satisfied, will open power to solenoid and valve will close to go into pump-down mode and low pressure controll will turn compressor off. third component is the defrost timer, with manual set pins for modes, this timer will give refrigeration mode, or defrost sequence ( evaporator heaters defrost ice buid-up in evaporator}, and basically is also wired in series to pumpdown solenoid to lower pressure and low-pressure controll turns compressor off, just like the cabniet t'stat does. if you want actual schematic, e-mail me and i can scan this diagram ?
lorenzopower
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| tav1017
| "Re(1):WALK IN FREEZER" , posted Thu 20 Apr 20:38
Thank you for your reply, Mr. Johnson. The defrost is set to run in three times a day each 1/2 hr. long. The problem I'm having is the compressor is taking longer to pump down in which the heaters then kick on causing a tripped breaker. A three 20 amp breaker and the total amp of compressor and heaters are 33 amps. Plus whoever installed the unit used 12 gauge wire instead of 10 or 8 gauge wire. Hope this makes some sense. Thanks
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| | rjohnson2152
| "Re(2):WALK IN FREEZER" , posted Fri 21 Apr 10:55
check the wiring on the defrost timer. What model defrost timer are you using? Sounds like they do not have the timer interlock wired correctly. This would prevent the compressor from running at the same time as the heaters are energized. This is usually done by wiring the compressor contactor through the aux contacts of the timer...if the timer is in defrost, there is no power to the compressor contactor preventing the comperssor from running. Email me the model of the equipment and the timer model and I will email you a wiring diagram to use. johnsonr1@asme.org or rjohnson24@cogeco.ca
Richard Johnson
Credentials:
BS Industrial Engineering Univ of Michigan 1986
BS Mechanical Engineering Univ of Ohio 1989
Member ASME NSPE RSES ASHRAE ASQ PMI IEEE
NATE Certified Master Technician
EPA Certified Universal
Certified Building Controls Engineer Honeywell TAC (formerly Control Systems International)
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| | TechMaster
| "Re(3):WALK IN FREEZER" , posted Tue 23 May 23:45
Just a note on this subject. After the compressor is pumped down during defrost, if the pressure in the crankcase rises enough to the cut-in setting of the LPC, then the compressor would run until it pumps down again. While it's running the defrost heaters would be off because of the n.c. aux. contact on the compressor contactor. The compressor is off on the LPC during defrost, not locked out.
Keep Cool!
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| | fitter597
| "Re(3):WALK IN FREEZER" , posted Mon 22 May 23:16
the timer on that system should only be used as a safety, you should have a clicks-on in the coil to terminate defrost at 50 to 55 degress, if you are cycling on the time you should check that.
"We Do It Right The First Time"
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| rjohnson2152
| "Re(1):WALK IN FREEZER" , posted Thu 20 Apr 09:32
On a call from the defrost timer, the sol valve should close, causing the system to pump down, thus causing the compressor to cycle off on low pressure. The defrost timer then energizes, locking out the compressor from cycling during the defrost cycle and energizes the strip heaters. If your having defrost problems, what type of defrost timer are you using and what settings is it set for. I have found the best timer to be the paragon line with settings for defrost 20 minutes 3 times a day. The defrost times should be set during low use times, where the freezer is either not used (door opened often) or during periods when the location is closed.
If there is anything more I can offer, please feel free to post here or email me directly.
Richard Johnson
Credentials:
BS Industrial Engineering Univ of Michigan 1986
BS Mechanical Engineering Univ of Ohio 1989
Member ASME NSPE RSES ASHRAE ASQ PMI IEEE
NATE Certified Master Technician
EPA Certified Universal
Certified Building Controls Engineer Honeywell TAC (formerly Control Systems International)
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| Xenos
| "Re(1):WALK IN FREEZER" , posted Wed 19 Apr 21:44
Refrigeration is a weak subject for me. I do have a thought though. During a defrost you would want to pump down the system to prevent the compressor from overloading on startup. I’m sure the refrigerant it’s self would be absorbing the heat during this period as well and that wouldn’t be too energy efficient.
I’m sure others can add quite a bit to this.
Xenos.
The best way to escape a problem is to solve it.
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