Page 1 of 6 123456 LastLast
Results 1 to 13 of 69
  1. #1
    Join Date
    Aug 2011
    Posts
    1,191

    very high head pressure with very low suction pressure

    went to customer home check on r22 heat pump cut out ,the pressure on high side is 400 lbs,and low side is 30 lbs in cooling mode,and it run 3mins and cut off each time u turn it on,and running in heat mode the pressure is normal,but still cut off in few mins,check the line voltage is normal,condenser coil is clean,indoor coil in new with tev,and running in heat or cool mode the suction line get correct temp(hot and cold real fast),he already have two tech come look at it,cant find out what is wrong,i think is new indoor coil restriction,or even system have more then one problemmaybe air in the system,but customer said it is new cant be!what do ur thinks?thanks

  2. #2
    Join Date
    Jan 2012
    Location
    Ottawa, Canada
    Posts
    1

    High head - low suction

    I'm new here, but a seasoned tech. To me I would be looking at your new coil. If the sensing bulb is not placed correctly, it will royally screw things up. Second, it is not uncommon to have a new, defective TXV. I have ran into it several times. Check the liquid line temp before and after the metering device. Check your delta "T" at the indoor coil. Make sure the house is not lacking return air(Very common in old houses), make sure the customers furniture is not restricting the return air grills upstairs. I would be checking different parts of the system with your thermometer. Ensure the fan is set at the proper cfm. In my opinion. it's always best to start at the basics. Hope this helps.

  3. #3
    Join Date
    Jan 2011
    Location
    Washington, D.C.
    Posts
    58
    Sound like you have a restriction in the system. Verify your airflow and check the TXV if used with the new coil if not piston maybe clogged, check temp across filter drier, look for an unintentional kink in lineset after the new coil was installed.
    Rise And Rise Again Until Lambs Become Lions!!!

  4. #4
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,533
    Despite what the customer says, you have to investigate a restriction. Did someone install a new LL dryer, or forget to change an old dryer because it is hidden in the OD unit?

    If the customer insists he is correct, you'll have to walk away.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  5. #5
    Join Date
    Jul 2009
    Location
    South Carolina
    Posts
    3,217
    This is a classic sign of a partial restriction that we argue about here around once a year. It goes against what we're taught but even with the proper charge it will cause extremely high head pressure. It obviously has to be down stream from wherever you're reading the high pressure. If you're reading is on the liquid line then the indoor coil would have nothing to do with it. The most common place would be the metering device or screen at the outside unit but as suggested it could also be a plugged dryer but that's pretty unlikely.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  6. #6
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,659
    Pony,

    You've posted problems like this before and have always been asked for the same information.

    Pressures alone don't mean anything.

    What is the superheat? What is the subcooling? What is your indoor airflow?

    Start taking a more comprehensive set of readings when you have a trouble system and you will find more problems, faster.


    Anyone posting a solution is doing little more than guessing without more data.

  7. #7
    Join Date
    Nov 2011
    Location
    USA
    Posts
    384
    Quote Originally Posted by pony View Post
    went to customer home check on r22 heat pump cut out ,the pressure on high side is 400 lbs,and low side is 30 lbs in cooling mode,and it run 3mins and cut off each time u turn it on,and running in heat mode the pressure is normal,but still cut off in few mins,check the line voltage is normal,condenser coil is clean,indoor coil in new with tev,and running in heat or cool mode the suction line get correct temp(hot and cold real fast),he already have two tech come look at it,cant find out what is wrong,i think is new indoor coil restriction,or even system have more then one problemmaybe air in the system,but customer said it is new cant be!what do ur thinks?thanks
    A cold suction line (low superheat) with low suction pressure is a symptom of low evaporator air. A liquid restriction would result high superheat (warm suction line). The high head probably due to the other guys overcharging, trying to get the suction pressure up.

    But the low air problem would result in high head pressure in the heat cycle.

    If the contactor is actually dropping out, I would guess a hi/lo pressure limit opening.

  8. #8
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    new coil does it has a 410-a txv or was it changed to a r-22 valve

  9. #9
    Join Date
    Jul 2009
    Location
    South Carolina
    Posts
    3,217
    Quote Originally Posted by garyed View Post
    This is a classic sign of a partial restriction that we argue about here around once a year. It goes against what we're taught but even with the proper charge it will cause extremely high head pressure. It obviously has to be down stream from wherever you're reading the high pressure. If you're reading is on the liquid line then the indoor coil would have nothing to do with it. The most common place would be the metering device or screen at the outside unit but as suggested it could also be a plugged dryer but that's pretty unlikely.
    My bad,

    I read the OP wrong, I thought it was fine in cooling but high head in heating so disregard this post. I'll have to read it over again.
    I'd still be looking at a restriction with those pressures but a little more info is needed about both cycles.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

  10. #10
    Join Date
    Jan 2011
    Location
    Washington, D.C.
    Posts
    58
    3 mins of runtime will not allow you to get an accurate superheat/subcooling reading so giving a solution to first correct the problem (3mins then cut off) is more than just guessing, then checking superheat/subcooling to specs to properly charge the system. Pressure alone in this instance is more than enough info. Come on now!!!
    Rise And Rise Again Until Lambs Become Lions!!!

  11. #11
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,659
    Iszell

    Read the OP's other posts.

    It is my opinion that he has no business touching an HVAC system beyond the thermostat.

  12. #12
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,659
    Pony,

    Did you determine why it "cuts off"?

    One would ASSUME high pressure, but assumptions are not part of good service practices.

    A new coils doesn't mean that you have good indoor airflow. This is why an airflow test is required.

    You state condenser coil is clean. Did you clean it or are we still assuming?

    And even with 3 minutes of runtime, you'll know if the superheat is high or low.

  13. #13
    Join Date
    Aug 2011
    Posts
    1,191
    any body think maybe compressor trip cause it have running with low freon for long time,maybe mechanicaly falier in compressor over heat and trip?that is one more thing i have to check amp draw from compressor,cause i am looking at the liquid line restruction and high and low pressure to long,lol,

Page 1 of 6 123456 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event