I changed two compressors this week both at the same site.Same type condensing units,low temp. ..R-404A...walk in freezers...pump down systems..rooftop condensing units..lab.building..maintaining -15 degrees in box.Compressor # AVA2490ZXT. Units have cond. fan cyclers only for head press. control.Both replacement compressors came without crankcase heaters and the originals did not have them either.The units do not have suction accumulators.Both replacement compressors had wells for self regulating type heaters and I thought it would be good refrigeration practice to apply heaters to the compressors.The supplier did not have self regulating type so I used 90 watt 230 volt band type. My delema came at the point of wiring them in.I've seen it done both ways .....across the line,hot all the time...and on normaly closed aux. contacts...hot only when the compressor is off.I chose to wire it hot all the tme.Did I make the right choice?I changed contactors,liq. line drier,installed suction drier,deep vac.,all the proper stuff,start up and check out went well,perfect super heat, temps. pressures,the whole nine,tested pump down, defrost,cycle controls and ,every thing checked out.One faild pump was grounded and the other had bad valves.I'm wondering if possibly the failures were a result of not having heaters in the first place.I know it"s a stretch? Any way Im more concerned about the heater wiring.Any thoughts??????,
Crankcase Heaters?
richper
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I changed two compressors this week both at the same site.Same type condensing units,low temp. ..R-404A...walk in freezers...pump down systems..rooftop condensing units..lab.building..maintaining -15 degrees in box.Compressor # AVA2490ZXT. Units have cond. fan cyclers only for head press. control.Both replacement compressors came without crankcase heaters and the originals did not have them either.The units do not have suction accumulators.Both replacement compressors had wells for self regulating type heaters and I thought it would be good refrigeration practice to apply heaters to the compressors.The supplier did not have self regulating type so I used 90 watt 230 volt band type. My delema came at the point of wiring them in.I've seen it done both ways .....across the line,hot all the time...and on normaly closed aux. contacts...hot only when the compressor is off.I chose to wire it hot all the tme.Did I make the right choice?I changed contactors,liq. line drier,installed suction drier,deep vac.,all the proper stuff,start up and check out went well,perfect super heat, temps. pressures,the whole nine,tested pump down, defrost,cycle controls and ,every thing checked out.One faild pump was grounded and the other had bad valves.I'm wondering if possibly the failures were a result of not having heaters in the first place.I know it"s a stretch? Any way Im more concerned about the heater wiring.Any thoughts??????,
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You my friend have made an excellent move. WHile a pump down system leaves little refrigerant in the evap during and off cycle or defrost (if wired correctly) the heaters , feel , are good insurance incase the pumpdown valve leaks by or someother reason you happen to get migration.
Depending on your climate and the ambient s encountered I prefer to have the heaters on all the time. If your application was for a refrigerator (higher operating temp) and you are in a warmer area (say some places in AZ, NM, OK, TX...) then I might want to use the on during off cycle only. I say this because the warmer operating a system is designed fopr the warmer the whole system is already, including the oil. And add this to a climate that experiences several days of over 100'f ambient the added heat of the heater could cause breakdown of the oil or inhibit lubrication.
Just my thoughts I could be wrong (as usual. Just ask my wife.).
Depending on your climate and the ambient s encountered I prefer to have the heaters on all the time. If your application was for a refrigerator (higher operating temp) and you are in a warmer area (say some places in AZ, NM, OK, TX...) then I might want to use the on during off cycle only. I say this because the warmer operating a system is designed fopr the warmer the whole system is already, including the oil. And add this to a climate that experiences several days of over 100'f ambient the added heat of the heater could cause breakdown of the oil or inhibit lubrication.
Just my thoughts I could be wrong (as usual. Just ask my wife.).
Thanks for the replies,my concern with them being on all the time is about our hot summer days to come and the fact that under such low saturation temps. mass flow rate will decrease causing higher than normal superheats.Add to that the crankcase heat and you may have a situation?...right??????
All of my outdoor condensing units cycle crank case heater on aux contacts compressor contactor. We insulate receiver and self regulateing heater remains on year round. The liquid injection on scroll compressors is engageing at 40 deg ambiant, tells me we need compressor cooling not CCH.
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83 Posts
Limit the CC Heater
Now I would feel better handing this off to someone with more experience in your application. Refrigeration is not all that different from AC. Refrigeration is the 1/4 horse, Refrigeration the Thoroughbred. Bothe horses but not the same job in mind. I dont think you will have trouble if its a freezer but I would want to see about using a higher temp limit say 70 or even 80'F. However this may be overkill because has the outdoor temp rises the longer run cycle you have also. And the need for CC Heat is diminished or gone completely.
So maybe using the standard 60'F limit would be ok. One way to check me out on this is to look at the data on the self regulating heater. At what temp does the wattage reduce to "trickle", or less than 80% of maximum? After I checked this I would use this temp of a limit.
BTW this limit is just like a domestic refrigerator defrost limit. And it hung with the limit "wire tied" to the wiring exposed to the ambient air inside the condenser. Reason for use -Keep oil temps within normal range.op:
A few years back I had to install low ambient controls on a Carrier/Bryant Split AC. 3 things in this kit: 1 A head pressure "peanut type" fan cycle switch, 2 A Crank Case Heater 3 A limit switch for the CCH. Thiswas carriers answer to limit the CC htr in warmer ambient weather and because no Aux contacts on contactor were available. I believe the switch opened around 60'F.
Now I would feel better handing this off to someone with more experience in your application. Refrigeration is not all that different from AC. Refrigeration is the 1/4 horse, Refrigeration the Thoroughbred. Bothe horses but not the same job in mind. I dont think you will have trouble if its a freezer but I would want to see about using a higher temp limit say 70 or even 80'F. However this may be overkill because has the outdoor temp rises the longer run cycle you have also. And the need for CC Heat is diminished or gone completely.
So maybe using the standard 60'F limit would be ok. One way to check me out on this is to look at the data on the self regulating heater. At what temp does the wattage reduce to "trickle", or less than 80% of maximum? After I checked this I would use this temp of a limit.
BTW this limit is just like a domestic refrigerator defrost limit. And it hung with the limit "wire tied" to the wiring exposed to the ambient air inside the condenser. Reason for use -Keep oil temps within normal range.
op:
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3,032 Posts
When some customers decide to turn the c/u off in the winter time and turn back on to start storing ice cream etc. (especially at gas station stores) that's when your CCH means nothing. I found that out by questioning a customer about the sequence of events. As far as wiring goes I like the idea of running the heater with the aux or if you don't have it you can wire it through a GP relay. But isn't the heater self regulating anyway ? Ah okey you said the supplier didn't have that one..
C/C htr clarification
majority of Tec & Cope cond units are indoor units yet are often used as outdoor units. These do not include C/C htrs, both mfrs make a few outdoor units which are supplied with C/C htrs, these are clearly labeled as such.
Bohn. Larkin. Russell and others make outdoor units clearly labeled as such (with C/C htrs).
Units not labeled "outdoor" don't come with C/C htrs!
majority of Tec & Cope cond units are indoor units yet are often used as outdoor units. These do not include C/C htrs, both mfrs make a few outdoor units which are supplied with C/C htrs, these are clearly labeled as such.
Bohn. Larkin. Russell and others make outdoor units clearly labeled as such (with C/C htrs).
Units not labeled "outdoor" don't come with C/C htrs!
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