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  1. #1
    Join Date
    Oct 2012
    Posts
    10

    Problems with walk in refrigerator/freezer

    Looking for a second opinion on this situation. Went to call and unit was not iced up, must have just came off defrost cycle or customer had it off and only turned it on when i got there. Asked customer if unit ever had problems or been serviced before, and of course said no. Ambient temp in cooler was 0-2 degrees F, but customer complained of ice cream melting. Upon inspection of condesing unit, found unit to be running to be what seemed normally. inspected condensing unit for about 30 min looking for any switches that could be bound or have burnt contacts and everything seemed alright, switches were all closed when they were supposed to . Checked pressures and all controls to see what may have opened and no switches were open. Suction pressure was high and discharge temp was a bit low. went downstairs to evap and evap coil was only iced up around the side of the unit where the txv and solenoid were located. went back upstairs to check pressures, and pressure dropped and unit shut off and went into defrost(fan cycling system w/defrost timer). did this about three times and now amb temp in cooler is at about 32 degrees and unit is still not entirely defrosting or cooling properly. It went into late night (16:30-18:00 (length of time spent) and customer did not want to pay OT so i'm going back tomorrow. oh yea, and compressor had been replaced(looked too new in such a decrepit unit) without suction line filter drier -_-, didn't check for acid in system but theres time for that tomorrow.

    system is r502, 3ph, 208/230vac.

    I'm thinking its one of these things:

    1) low on refrigerant (didn't want to jump to conclusions because i knew super-heat/ sub-cooling would be off with unit frozen. wait till tomorrow to check)

    2)moisture in refrigerant, plugging txv and thats why that side is icing up. need to recover refrigerant and replace with virgin refrigerant

    3) Txv going bad, losing thermal charge

    4) bad pumpdown solenoid

    5) bad compressor valves which indicate high back pressure?
    -with this, would the compressor be drawing high amps?

    6) fan cycling control binding up? i don't see how that could do it though. the compressor would be sending hot gas thru the evaporator essentially keeping it in the defrost cycle, right?

    I have 5 yrs experience installing furnaces, a/c/ and ductwork, but I'm new to servicing refrigeration so help would be appreciated. Thanks for any and all help.

  2. #2
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    what were the pressures......
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  3. #3
    Join Date
    Oct 2012
    Posts
    10
    60psig on the low, 180 on high. temp outside was about 76 degrees

  4. #4
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    indeed.... suction pressure real high.... need to check superheat. .... sounds like compressor troubles
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  5. #5
    Join Date
    Oct 2012
    Posts
    10
    yeaaaaa i was thinking the same thing. when i saw it was a new compressor with-out the suction line filter drier, it made me wonder. On ANY unit i've replaced or watched someone replace a compressor, they always added the suction line drier. Last one i replaced with the senior tech, we tested refrigerant for acid(came up positive), replaced compressor, added acid neutralizer, suction line drier, and next test was negative and unit was good to go. When I go back tomorrow ill check superheat after about 10 min of unit running because it took 30 for it to ice up. What exactly would i be looking for as far as superheat readings that would indicate compressor troubles? or a bad txv charge for that matter? If it has a low superheat then the unit would be getting liquid back to the compressor(therefore damaging it) and if it has a high superheat, the evaporator is starved and compressor is overworking (also causing damage). really curious and looking forward to seeing what the issue is at this

  6. #6
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    I have been around a while trust me..... a suction filter has its place....I have used maybe 10 in 30 years.....
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  7. #7
    Join Date
    Oct 2012
    Posts
    10
    k, whats the appropriate way to use them then?

  8. #8
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    on bad burn outs...suction line driers are for clean up ...not meant to be left in system permanently
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  9. #9
    Join Date
    Oct 2012
    Posts
    10
    thanks for the info, much appreciated. the ones that i have worked on with the senior tech in particular were bad burnouts, and we installed the HH style drier. back to the compressor though, would superheat solely indicate that there is compressor trouble?

  10. #10
    Join Date
    Dec 2011
    Location
    New Zealand
    Posts
    2,185
    Your choice of words maybe in correct.

    You talk about "defrost" happening all the time. Cycling on and off should not cause the evap to go into defrost. Are you sure that you are introducing heat required for defrosting?

    What type of defrost is it, electric, hot gas, reverse cycle!

    If the room temp rise then your load rise and you will get high suction pressures. You indicate that the suction pressure drops then goes off. So the comp does seem to be working.

    If the end tubes are frozen (and happens over along period) it could be that the expansion valve bulb is covered in an ice ball, causing the TXV to act strangely (not common but no unheard of).

    Clear all ice first! A clean start.

    Start the system with out the fans running (keeping a eye of the system) You should see the suction pressure drop and the evap freeze evenly.

    If this happens then, we are moving in the right direction.

    Now reconnect the evap fans, we would expect to see a high suction and likely high superheat, the room should fall in temp quite quick (if empty and limited load), when are getting closer to the desired box temp, the evap pressure should fall along with the superheat becoming under control.

    If this is all OK, then you need to investigate the controls,

  11. #11
    Join Date
    Jan 2010
    Location
    Vancouver Island
    Posts
    342
    Make doubly sure you have cleared all the ice of the evaporator coil. Get your flashlight and check between all the fins all the way through the coil. Iced up refrigeration coils can be clogged with ice and it can take awhile to get it all melted.

    Sent from my Transformer TF101 using Tapatalk

  12. #12
    Join Date
    Oct 2012
    Posts
    10
    its a hot gas defrost system. and it was only the side of the expansion device and pump down solenoid that was iced up, not the entire evaporator coil which is what lead me to believe that it could be a problem with the txv or there could be moisture in the system. as i said im going back today and will find out and let everyone know. thanks for all the advice

  13. #13
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,587
    Quote Originally Posted by akerilla View Post
    system is r502, 3ph, 208/230vac.

    I'm thinking its one of these things:

    1) low on refrigerant (didn't want to jump to conclusions because i knew super-heat/ sub-cooling would be off with unit frozen. wait till tomorrow to check)
    60psi suction? You think this is low?
    2)moisture in refrigerant, plugging txv and thats why that side is icing up. need to recover refrigerant and replace with virgin refrigerant
    60psi suction? You think txv is plugged?
    3) Txv going bad, losing thermal charge
    Txv losing charge? How long does it usually take for a powerhead to lose its charge?

    4) bad pumpdown solenoid
    60psi suction? You think the pumpdown solenoid is bad?
    5) bad compressor valves which indicate high back pressure?
    -with this, would the compressor be drawing high amps?
    Why would you have excessive amps?
    6) fan cycling control binding up? i don't see how that could do it though. the compressor would be sending hot gas thru the evaporator essentially keeping it in the defrost cycle, right?
    180psi head? You think fan cycle is binding?
    I have 5 yrs experience installing furnaces, a/c/ and ductwork, but I'm new to servicing refrigeration so help would be appreciated. Thanks for any and all help.
    So let me get this straight. No ice on the coil when you arrived. Box @ 0-2 degrees. Was this temp measured with the box thermometer or your digital? Unit ran for 1/2 hour while you checked electric and now you have ice around txv. Was there ice around txv before this? What's wrong with ice on the txv? Did you check? Pressure dropped and unit went into defrost and cycled fan??? 3 times? This sentence makes no sense, please rephrase it.

    This is a freezer, not a cooler as you originaly stated? What type of defrost? Does it pump down?

    Think about all that was said. Let us know what you found.
    Last edited by 2sac; 10-16-2012 at 08:30 AM.
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