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  1. #1
    I am somewhat confused about the need to preheat the crankcase oil and refigerant of a heat pump before starting.

    I am having a Carrier 25HNA6 3 ton heat pump installed. The installation manual clearly states that the unit should be connected to the source power for a minimun of 24 hours before the compressor is run. Specifically for my unit the manual states that : "... starting the compressor without a minimum of 12 hours of crankcase heat prior to initial start-up may result in a compressor chattering noise and possible damage to the compressor".

    The installer stated that this was not necessary at the current outside temp (55 F). How do I reconcile these two opposing statements. Also, if the crankcase heat is that critical why is there not a thermistor that prevents operation of the compressor unless it is at a certain temp. It would not be unheard of for the power to fail for several hours while the occupant is not at home in the winter with outside temps well below freezing. In such a case the compressor would automatically restart when the power was resumed -?damaging the compressor. The manufactures statement seems critical and alarming, yet I suspect most heat pump owners are oblivious to this concern and the manufacturer does not include any design features to deal with the issue. This is very confusing for the consumer. Does anyone know the truth?

  2. #2
    Join Date
    Mar 2003
    Location
    PA/DE area
    Posts
    1,535
    We use paint dryers to warm them up!!
    It's NOT the BRAND,it's the company that installs it!!!!!

  3. #3
    Join Date
    Nov 2006
    Location
    Gloucester Virginia
    Posts
    20

    Cool

    A compressor is not designed to pump liquid refridgerant so keeping the compressor warm helps prevent liquid from migrating to the sump during the off cycle in cool weather. If you keep the sump warm any liquid that happens to reach the compressor will be boiled off!! Hopefully. You are probably allright to start the system but the manufacture recommends allowing time for the boil off process.
    heattech

    If it hasnt worked properly since you serviced it last then why did it take the customer 2 years to complain??

  4. #4
    Join Date
    Apr 2004
    Posts
    7,680
    What Carrier is saying is.... IF there is a crankcase heater installed, you should power it up a minimum of 12 hours before starting the comnpressor to purge any liquid refrigerant from the compressor. As the previous poster pointed out compressors cant pump liquid.

    Refrigerant, when not being pumped will migrate. It will migrate to the coldest point. At 55 degrees outside, you can pretty much bet that that the outdoor unit is the coldest spot. Also, the mfg's ship the units with a full charge of refrigerant stacked up in the outdoor coil. When the Heat pump is started in the heating mode, you have all of about 10" of suction line between that fully logged coil and the inlet of the compressor. This could kill a reciprocating compressor almost instantly. A scroll will generally be noisy and live through it without any issues.

    The reality is, that unless the unit is wired in and piped in one day, they would have to return the next day to perform the start up. You would either have to live with the emergency heat on for the night (forcing more refrigerant to migrate outside) or find another source of heat. It's one of those catch 22's. The right thing to do is power it up for a day, but it doesnt happen very often.

    I suppose they could ship the equipment with a nitrogen charge. And that would be fine with me, but the problem then is, more often than not, it will get started before a proper charge is in the system. Potentially the compressor could pull into a vaccuum. Scrolls dont like that and frankly it's not healthy for a recip.

    Also, split systems are not run tested the way you might think. You cant run them for long with nothing hooked up to them. Generally it's a bump test where the compressor, motor are started and stopped loong enough for the run test machine to pick up on the current they draw. What I am getting at is, even s short run time can pump oil out of the compressor into the coil.... No go back to the flooding condition at start up... The refrigerant itsef is a solvent, not a lubricant. With little oil in the compressor, the refrigerant can allow parts to run dry.

    Ok... Your unit started... Dont let it bother you.

  5. #5
    Join Date
    Oct 2006
    Location
    Emerald Coast, FL 30.1N 85.8W
    Posts
    681

    need heater to kick out the refrigerant

    crankcase heaters prevent the freon from migrating to the oil; otherwise, compressor damage could result.

    Originally posted by northern_comfort
    I am somewhat confused about the need to preheat the crankcase oil and refigerant of a heat pump before starting.

    I am having a Carrier 25HNA6 3 ton heat pump installed. The installation manual clearly states that the unit should be connected to the source power for a minimun of 24 hours before the compressor is run. Specifically for my unit the manual states that : "... starting the compressor without a minimum of 12 hours of crankcase heat prior to initial start-up may result in a compressor chattering noise and possible damage to the compressor".

    The installer stated that this was not necessary at the current outside temp (55 F). How do I reconcile these two opposing statements. Also, if the crankcase heat is that critical why is there not a thermistor that prevents operation of the compressor unless it is at a certain temp. It would not be unheard of for the power to fail for several hours while the occupant is not at home in the winter with outside temps well below freezing. In such a case the compressor would automatically restart when the power was resumed -?damaging the compressor. The manufactures statement seems critical and alarming, yet I suspect most heat pump owners are oblivious to this concern and the manufacturer does not include any design features to deal with the issue. This is very confusing for the consumer. Does anyone know the truth?

  6. #6
    Thanks for the your help, but what about the issue of power failures during the winter. How does when prevent this possible compressor damage especially if the power outage happens when no one is at home?

  7. #7
    Join Date
    Oct 2004
    Posts
    3,400
    Originally posted by northern_comfort
    Thanks for the your help, but what about the issue of power failures during the winter. How does when prevent this possible compressor damage especially if the power outage happens when no one is at home?
    You are correct. There is no automatic feature that keeps the comprssor from running until the oil is warm. The reason heat pumps do not have this feature is simply a lack of demand. The chances of an extended power outage and unattended startup are pretty slim. Also, the chances of damaging the compressor on a cold startup are way less than 100%. The manufacturers put this statement in the installer's literature as a CYA.

    While being a valid statement, you still have about as good a chance of winning the lottery as you do of killing your compressor after a power outage, with unattended startup. If you want to lessen the chances, just turn it off when the power goes off. Then you can choose how long to wait (in the cold) after the power comes back on.

  8. #8
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,210
    Yes, Kevin, your right! Carrier recommends that the compressor stay off after a power outage as long as the electrical outage lasted, once the power is restored. But I wonder how really important that is.

    Thorton
    ______________________
    Opportunity is not a mater of chance, it is a matter of choice; it is not a thing to be waited for, its is a thing to be achieved


  9. #9
    Join Date
    Apr 2004
    Posts
    7,680
    Copeland will tell you, (if you ask nicely) that a compressor can be off for up to 2 hours and still hold enough heat in the motor to eliminate the need for a CCH.

    If you have an extended power outage, you should probably pull the power fro the unit anyway. 2 reasons. 1st, you can help reduce the start up load on the house and utility by not having every compressor in the area restarting at once. and 2nd. Until the power is back on solid you dont want brown out or flickering to pound your unit. After the power is restored, you can turn it back on.

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