walk in wine cooler
this walk in wine cooler the evap section has been in place for about 10 years and the condenser was replaced about 5 years ago. according to the home owner pretty nice guy. last time our company serviced his wine cellar was about 1.5 years ago. I went like mid last week found evap coil frozen unit has 2 evap fans the left one was bad. hmmm pretty straight forward bad fan motor, the original motor was 14 watt suppliers only stock 16 watt so I used that. its the little black motor usually seen in condensers. its about 1/2 inch fatter so the blade sticks through the shroud about 1/2 or less than originally I don't think it makes much of a difference because the cutting edge of the scoop stick out more in turn will scoop more air, the higher end of the blade where the air flies off still sticks up through the shroud so it is moving the air. now about 5 days later on the weekend on call guy gets aa call unit is frozen. he doesn't do refrigeration he defrost it and fired it back up it was Saturday I went back today Monday unit was at 53 degrees and not frozen it was off on temp. evap. heat craft m#c30af s# d01j07619 condenser Copeland m# fatm-a075-1av-020
s# 11a10608u r134a sight glass at the condenser is clear 22low/195 hi psig unit has a receiver I forgot my subcool. superheat was 27 degrees. nameplate specs comp rls 6.9 actually I was drawing 7.5amps so even if I opened my txv my amps will climb higher. box temp was 55 degrees. 27 degrees superheat I feel is good because basically this is a cooler setup just operating at a higher temp. thermostat is set at 56 degrees cut in cut out was 53 degrees. im worried its going to freeze again. looking for some input
Two things come to mind from what you said:
1. Evaporator fan shroud should bisect the blade depth. Easiest way is is to line the blade's hub up with the shroud. If not done properly, airflow isn't right.
2. TXV setting should be desired superheat at desired temp setpoint. So...superheat is way off for 55 degrees.
That's my two cents. I've never worked on a W/I wine cooler. Somebody here will certainly give you more feedback.
195# head seems high, unless it was really hot that day... Make sure condenser is clean!
Superheat 27 degrees, at compressor or evap? If that's compressor superheat then that's perfect. But if thats evap superheat then way too high. Don't choke the TXV to control amp draw. Use a CPR valve for that if necessary. Set the TXV for proper evaporator superheat (10*).
Thanks for the input about the fan blade position I believe I understand what u mean! Basically the center flat area should be even with the shroud pretty much 1/2 the blade will be on one side and 1/2 on the other???? Hopefully I'm explaining it smooth
Originally Posted by ECtofix
Yep it's compressor superheat sorry I don't add that part I try to give as much as possible thanks
Originally Posted by trippintl0
195 is to hi..... what controls the compressor.....hopefully temperature control
it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair
the high pressure is okay if it's hot, well it's hot at miami. Your thermostat is set to 56 degree, it shouldn't frost at all imo. Check your thermostat, see if it's working properly, check the position of it. Best bet is thermostat failure.
It's an electronic thermostat Johnson control a419, I Was playing with it testing it. Seems to work properly. It had a feature that if it had an issue with the sensor you can allow the unit to continue to run. It was set at that so maybe intermittently its screwing up so I changed the setting to if it has an issue it shuts down the unit!! So if he was to call now and say his cellar is hot then sounds like the thermostat is acting up so I'll have to wait and see
Originally Posted by EEAllen
it's a pump down system. And of course a low pressure control in the condenser shutting down the compressor. It has an external thermal overload to protect it. Wasn't sure what your question was reffering too
Originally Posted by carmon
If the replacement motor isn't dimensionally the same as the OEM motor so the fan blade isn't in the correct position, the airflow will be affected significantly. I suggest getting the proper OEM replacement from Heatcraft. A low airflow will tend to cause loss of capacity and the coil will run colder than design.
I assume you're talking about a GE cast iron unit bearing motor. They usually go from a 9 watt size to 16 watt....I've never seen a 14 watt.
Look up the capacities of the condensing unit and the evaporator and you'll find they balance out at about 6500 Btuh with a rather large 22ºF TD. This means that if all is to specs, with a 56ºF box temp, your evap temp should be 56-22 = 34ºF...or above freezing. (Your stated suction pressure of 22 psig corresponds to a 20ºF evap temp.) This is a medium temperature condensing unit with an operating envelope which tops out at 25ºF SST. It really should have been a high temp unit for this application.
Also, the Copeland specs for the FTAM-A075-IAA R134A condensing unit shows a compressor RLA = 11.8 Amps and at 90ºF ambient and 25ºF Evap temp the condensing temperature should be about 122ºF or around 175-180 psig.
If it freezes again I'll have to order the original evap fan motor. I'm sure it was a 14 watt no one stocked it so I had to to with the 16 watt. That could be my issue. Even though to me it feels like the same air across both fans but that's the answer I'm looking for so I side more with that. also almost and reality are two different things. But my 22 Psig corresponds to 25 degrees. On my pt chart. you've stated a lot of useful info as usual, maybe the numbers got crossed or u calculated in some correction factor your capable in doing that. Either way I'm stil off by 10 degrees td! So my input didnt make a difference thanks for the info
Originally Posted by icemeister
No corrections factors were used for what I posted. I only came up with a quick estimate of how the condensing unit and coil you have "should" balance out for a 56ºF box.
If you were to take into consideration your measured evap temp of 25ºF, then the TD would be 56 - 25....or 31ºF TD. This "could" be due to a high evaporator superheat, or possibly a significant pressure drop in the suction line...since I assume your suction pressure was taken at the compressor and not at the coil.
Also, I've found that many commercial evaporators don't perform up to specs in the real world. I was told by a factory engineer many years ago that these coils, unlike A/C coils, are not AHRI tested and rated, so the manufacturers fudge the number a bit...up to 35% or so. It's called "commercialized" ratings.
If the customer has had some type of change of use as in overloading the wine cooler or the insulation anywhere in the walls or at the gaskets for the door(s) create humidity infiltration then you can get a frozen coil even if the refrig unit is working correctly.
I also put in a 8 to 10 degree differential on the controlling thermostat to allow the coil to defrost. And, at times, I will wire the fans to run all the time for a much better defrost. The coil itself can get gummy and hold on to the condensate. Or the drain line may have lost it's prime and is sucking humid air back through the coil and that will definately freeze a coil.
All things to check but make sure the unit is cycling off on temperature and not short cycling.
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