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  1. #1
    Join Date
    Jan 2007
    Location
    Southeast, GA / Jacksonville, FL
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    263

    This is what i got...

    Just started working with this commercial maintenance company (mostly banks and strip malls).

    Me and another tech go to service call at this bank the unit is a Lennox rtu heatpump mod:CHP16-653-9Y. He takes the cover off and looks and finds unit frozen. He says he dont know why its doing it (he is not really a HVAC tech, he is a maintenance tech).

    I ask him the history of the unit. he says last time he was here it was off on high pressure switch. I told him it might be a restriction or txv, he says he doesnt think so he thinks its low charge and tells me to come by tommorrow and add some 22 and see what it does.

    I return the next morning and start unit up pressures are a little low (didnt let unit run long) added about a lb of r22 68F outside, 72F inside pressures at 50 and 250,subcooling high, cannt remember what i had for superheat. Called tech up and told him i think there is a restriction or txv failure.

    Next day,,,Service call to same bank, go by today and find unit frozen up. Thaw out and check pressures 50 / 55 and about 275 with 72 outside temp (didnt get return). I called bad txv.... What do you guys think.

  2. #2
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,337
    Quote Originally Posted by navyhydronics View Post
    Just started working with this commercial maintenance company (mostly banks and strip malls).

    Me and another tech go to service call at this bank the unit is a Lennox rtu heatpump mod:CHP16-653-9Y. He takes the cover off and looks and finds unit frozen. He says he dont know why its doing it (he is not really a HVAC tech, he is a maintenance tech).

    I ask him the history of the unit. he says last time he was here it was off on high pressure switch. I told him it might be a restriction or txv, he says he doesnt think so he thinks its low charge and tells me to come by tommorrow and add some 22 and see what it does.

    I return the next morning and start unit up pressures are a little low (didnt let unit run long) added about a lb of r22 68F outside, 72F inside pressures at 50 and 250,subcooling high, cannt remember what i had for superheat. Called tech up and told him i think there is a restriction or txv failure.

    Next day,,,Service call to same bank, go by today and find unit frozen up. Thaw out and check pressures 50 / 55 and about 275 with 72 outside temp (didnt get return). I called bad txv.... What do you guys think.
    Come on you know what everyone is going to ask.......What was the airflow?

  3. #3
    John Culpepper's Avatar
    John Culpepper is offline CHANGE YOUR EMAIL ADDRESS Professional Member*
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    Oct 2007
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    Austin Texas
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    Evap clean? Any temp drop across liquid line filter? I usually will thaw the unit out, fire it up and see where the frost starts forming.
    Nemo me impune lacessit.

    How much blood do I have to bathe in to get clean?

    Don't look down on anyone unless you're helping them up.

  4. #4
    Join Date
    Mar 2003
    Posts
    7,326
    if i were going to guess, i would say dirty filters in old return filter grilles inside the store causing low evap flow. someone thinks there are only filters on the roof, so they keep them clean. they only charge by suction pressure, so it is slightly overcharged. OR filters hadnt been changed enough, and evap coil has a high pressure drop across it indicating it is dirt logged....unit exhibits same conditions, and is overcharged.

  5. #5
    Join Date
    Jan 2007
    Location
    Southeast, GA / Jacksonville, FL
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    263
    Quote Originally Posted by John Culpepper View Post
    Evap clean? Any temp drop across liquid line filter? I usually will thaw the unit out, fire it up and see where the frost starts forming.
    Checked evaporator and filters, evap looked good didnt check drop across filter because freeze up didnt extend back to the filter-dryer (stopped/started at the txv).

    Observed system operation for about 2 hrs but no frost forming.

  6. #6
    Join Date
    Jan 2007
    Location
    Southeast, GA / Jacksonville, FL
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    Quote Originally Posted by ascj View Post
    Come on you know what everyone is going to ask.......What was the airflow?
    airflow seemed pretty good (dont have a air flow meter so dont know exactly)

  7. #7
    Join Date
    Jan 2007
    Location
    Southeast, GA / Jacksonville, FL
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    263
    Quote Originally Posted by flange View Post
    if i were going to guess, i would say dirty filters in old return filter grilles inside the store causing low evap flow. someone thinks there are only filters on the roof, so they keep them clean. they only charge by suction pressure, so it is slightly overcharged. OR filters hadnt been changed enough, and evap coil has a high pressure drop across it indicating it is dirt logged....unit exhibits same conditions, and is overcharged.
    Sound like a bad experience.

  8. #8
    Join Date
    Sep 2005
    Posts
    155
    You are having airflow issues if the txv is not freezing upon startup. Look for collasped duct or a fire damper in duct. Look at condensor if it is dirty your head presssure will be elevated and suction could be low if unit is low on charge.

  9. #9
    Join Date
    Sep 2006
    Location
    Chicago
    Posts
    474
    To diagnose a txv your going to need to know superheat numbers. It won't be that hard to figure out. If you got an airflow problem or any problem with air movement your going to have little superheat and low suction. If the txv is bad or the screen is plugged your going to have high superheat. If you have high superheat low suction your going to have to determine if it's from a leak or the txv being bad. A leak would be more common. If you do decide to change the txv pull the charge and be sure to weigh it as you take it out so you know where you stand.

    Also if you have high superheat and wonder if its low on charge pump it down and add a sight glass to ensure solid column to expansion valve or get some subcooling numbers. I will be you have an airflow issue. Not confusing yourself is the key.

  10. #10
    John Culpepper's Avatar
    John Culpepper is offline CHANGE YOUR EMAIL ADDRESS Professional Member*
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    My first course of action would be to recover, replace LLF and charge with virgin refer to nameplate and see if that cures it. Sometimes non-condensables will play havoc on a TXV. If you vacuum the hell out of it, if your lucky that will be the end of it.(fingers crossed)
    Nemo me impune lacessit.

    How much blood do I have to bathe in to get clean?

    Don't look down on anyone unless you're helping them up.

  11. #11
    Join Date
    Jan 2007
    Location
    Southeast, GA / Jacksonville, FL
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    263
    Quote Originally Posted by John Culpepper View Post
    My first course of action would be to recover, replace LLF and charge with virgin refer to nameplate and see if that cures it. Sometimes non-condensables will play havoc on a TXV. If you vacuum the hell out of it, if your lucky that will be the end of it.(fingers crossed)
    May do exactly that. Hope that cures it.

  12. #12
    Join Date
    Dec 2006
    Location
    Middle Tennessee
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    i would say more of a restriction than dirty evap because of the high head



    .

  13. #13
    Join Date
    Feb 2010
    Location
    Front Royal Va
    Posts
    82
    If you can pull some doors off of the unit to try to eliminate duct work as the problem.also amp check blower motor it should be with in 10 percent of rla

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