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  1. #1
    daniel nantell's Avatar
    daniel nantell Guest

    Default Heat pump testing-a/c mode

    I know during cold weather with a conventional gas furnace and outside condensing unit, you do not test the a/c unit during temp . below 60 degrees as it will cause the migration of oil out of the compressor. Does a Heat pump work the same way, not advisable to run the A/c mode in colder weather and how do you check the electric back up furnace is temp is not cold enought to cause the Electric back up furnace to kick on. I don't see many heat pumps in my area but need to know. thanks

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  2. #2
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    Default Re: Heat pump testing-a/c mode

    Not a problem with the a/c in cold weather, in fact the unit is switched to "cooling" without the outdoor fan running for the defrost cycle. Heat pumps are more robust than their cooling only cousins. You don't want to run it in the heating mode when outdoor temps are too WARM to keep from overheating/high head on the compressor. The electric heaters are typically controlled by the indoor stat, not outdoor ambient temperature. Set the indoor stat one or two degrees higher than indoor temperature to call for first stage heating (the heat pump) and confirm proper operation. Then raise the setting several degrees to call for back-up resistance heat and confirm operation. Then move the system switch to "emergency heat" setting to shutdown the outdoor unit and confirm you are still getting heat (although less than with the outdoor unit contributing) and that the outdoor unit did in fact shut off. You may have a different control system, especially if you have a multi-fuel set-up, but the explanation above fits the vast majority in our milder climate. You may also see an exterior thermostat designed to keep the heat pump from running in low ambient situations.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  3. #3
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    Default Re: Heat pump testing-a/c mode

    Quote Originally Posted by daniel nantell View Post
    I know during cold weather with a conventional gas furnace and outside condensing unit, you do not test the a/c unit during temp . below 60 degrees as it will cause the migration of oil out of the compressor. Does a Heat pump work the same way, not advisable to run the A/c mode in colder weather and how do you check the electric back up furnace is temp is not cold enought to cause the Electric back up furnace to kick on. I don't see many heat pumps in my area but need to know. thanks
    By the way, the reason for not running the A/C in cold weather is NOT oil migration. The reason is liquid slugging. Compressors are designed to compress refrigerant VAPOR, not LIQUID. Liquid refrigerant will migrate to the compressor during cold weather and settle there and in the suction line and will be immediately sucked into the compressor suction port when energized and tend to damage valves, rods, and pistons.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  4. #4
    Ted Menelly's Avatar
    Ted Menelly Guest

    Default Re: Heat pump testing-a/c mode

    I have operated AC in the temps in the upper 30s, 40s, 50s, 60s for as long as there has been AC condensers. I guess I am the lucky one that nothing has ever happened because they were my own that I was operating.

    Never had problem one.


  5. #5
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    Default Re: Heat pump testing-a/c mode

    Ted, back in the olden days when you and I were comin' up, they put crankcase heaters on the units to prevent damage but now those are "options" on most residential equipment. I run equipment colder than I ought (did I just say that out loud?) but only with what little knowledge I have from assessing the equipment and weather history. I have been around when compressors are slugging liquid and it is not something you want to repeat. It makes me want to hit the deck for fear of something coming apart! It is NOT a good sound!

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  6. #6
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    Spring Hill (Nashville), TN
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    Default Re: Heat pump testing-a/c mode

    If the unit has a Scroll compressor you can run the A/C at any temp and it won't be damaged.

    Scott Patterson, ACI
    Spring Hill, TN
    www.traceinspections.com

  7. #7
    Ted Menelly's Avatar
    Ted Menelly Guest

    Default Re: Heat pump testing-a/c mode

    Quote Originally Posted by Jim Luttrall View Post
    Ted, back in the olden days when you and I were comin' up, they put crankcase heaters on the units to prevent damage but now those are "options" on most residential equipment. I run equipment colder than I ought (did I just say that out loud?) but only with what little knowledge I have from assessing the equipment and weather history. I have been around when compressors are slugging liquid and it is not something you want to repeat. It makes me want to hit the deck for fear of something coming apart! It is NOT a good sound!

    I have no idea what you are talking about. I am only 28


  8. #8
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    Default Re: Heat pump testing-a/c mode

    28 and holding?

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  9. #9
    Nolan Kienitz's Avatar
    Nolan Kienitz Guest

    Default Re: Heat pump testing-a/c mode

    Quote Originally Posted by Jim Luttrall View Post
    28 and holding?
    Sounds very good!

    My Mom was "39 and holding" to the day she went Home a few years ago at the wonderful age of 92!

    Miss both her and my Dad to be able to sit and talk over things.


  10. #10
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    Default Re: Heat pump testing-a/c mode

    What would slugging actually sound like?

    The MAZZA INSPECTION GROUP
    www.mazzainspections.com
    Level III Thermo-picture-taker-er...er

  11. #11
    Join Date
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    Connecticut
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    Default Re: Heat pump testing-a/c mode

    slugging sounds like an NBA game
    without the sound of the ball bouncing
    and without the sound of the crowd cheering
    depending on what neighborhood you live in


  12. #12
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    Default Re: Heat pump testing-a/c mode

    If it runs in heat mode it is likely going to run in the cooling mode as the only item which changes is the reversing valve.
    How Does a Heat Pump Work? Heat Pump Association
    http://t1.gstatic.com/images?q=tbn:ANd9GcR2n8oOCP4QC4MNX8E0WO5Sc9eqgqX74 qD8WJQUcnU1Zzy7cSbAhttp://www.heatpumps.org.uk/HowDoesAHeatPumpWork.htm


  13. #13
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    Default Re: Heat pump testing-a/c mode

    Quote Originally Posted by Ted Menelly View Post
    I have no idea what you are talking about. I am only 28
    I liked 28 so much that I have done it twice and now working on the third time. Like a good movie you can see it more than once.


  14. #14
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    May 2010
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    No. San Diego Co., CA
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    Default Re: Heat pump testing-a/c mode

    I don't see too many electric heat pump a/c units in this mild climate but ran across one yesterday - relatively newly installed. The attic install looked okay but I could only get warm air out of the registers. The (split package) condenser was operating and I ran the system for a good 20-30 minutes but no change in temp. Any ideas?
    I did perform testing as outlined in the original post. Thanks in advance...


  15. #15
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    Default Re: Heat pump testing-a/c mode

    Quote Originally Posted by Ian Page View Post
    I don't see too many electric heat pump a/c units in this mild climate but ran across one yesterday - relatively newly installed. The attic install looked okay but I could only get warm air out of the registers. The (split package) condenser was operating and I ran the system for a good 20-30 minutes but no change in temp. Any ideas?
    That sounds like it needs attention from a heating professional. The weather is not that cold where you are, so you should get AC when you ask for it. I would not let that slide. $$$$

    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  16. #16
    Join Date
    May 2010
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    No. San Diego Co., CA
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    562

    Default Re: Heat pump testing-a/c mode

    John...No I didn't (let it slide). I learned, later, that a friend of a friend, of a friend did the installation - so I'm happy that I called out the deficiency in the report, advising a complete evaluation of the system was indicated/recommended.


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