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  1. #1
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212

    Heat Pumps are not Air-Conditioners.

    The title was just marketing. I'm interested in differences.

    Up to now, I have mostly been checking heat pump
    performances by putting them in cooling mode, verifying
    that they cool well, before moving them to heat mode.

    For folks that actually see a lot of heat pumps, are there
    some things about running them in A/C mode that are
    different than your typical A/C-only unit?

    #1 What is a fairly typical return air grill versus
    supply register temp difference in HEAT mode?
    In A/C mode, with newer (better airlfow) installations,
    14 degrees is typically what I see.

    #2 Does gauge behavior vary with heat pumps?
    In cooling, I was seeing my suction side go WAY down before
    creeping back to normal. I was thinking maybe
    the check valves take a bit of time to close off
    or something, or should gauge behavior be identical?
    And fluttering, my suction gauge fluttered about five-plus psi
    for about five seconds before dropping. I have never seen
    that in A/C-only units.

    #3 In cooler, maybe 45 degree weather, does the
    TXV for heating almost immediately frost or could that
    point to a problem?

    #4 Not quite on topic, but do the test terminals on
    defrost boards have some DEFINITE way of working?
    I rarely find manuals with units, and am always leery
    (more scared) about jumpering test terminals. Do you
    always jump test to common or force defrost to common
    or force defrost to test? Are test terminals typically
    tolerant of being jumpered to ground or 24V, regardless
    of what they are SUPPOSED to be jumpered to?

    #5 From the very vague instructional articles I've read,
    check valves seem to be mysteriously built into TXV's
    and the like. But I'm thinking they are actually very separate
    piping coming off both ends of the TXV. Am I wrong or
    am I right?

    Any other bits of enlightenment are welcome. When I
    am actually working with a troubled unit, I tend to forget
    every bit of basic theory about them. Stuff I read on here
    tends to stick better.

    Really, I want generalities, if they can be relied upon.
    If there are none, then that would be useful too. I mean,
    should I be looking into truck driving if I meet up with too
    many heat pumps? The bad ones are kicking my head.

  2. #2
    Join Date
    Jul 2005
    Posts
    5,518
    Quote Originally Posted by georgelass View Post
    The title was just marketing. I'm interested in differences.

    Up to now, I have mostly been checking heat pump
    performances by putting them in cooling mode, verifying
    that they cool well, before moving them to heat mode.
    The problem with that is that it's generally cooler out when you're checking or repairing a hp in heat mode and the indoor load will generally be low as well. IOW it's generally too cool out to check the system thoroughly enough in cooling mode, except to see that it runs and that the charge is in the generally correct range. That isn't to say that this will be totally useless info, but it is very limiting. It tells you nothing about how "well" the system will run in heating mode, only that it will/should also "run" in heating mode. In some cases it'll be warm enough to verify the charge, in some cases you'll still be guessing whether the charge is correct or not. This is something that experience and a little study will help you with.

    For folks that actually see a lot of heat pumps, are there
    some things about running them in A/C mode that are
    different than your typical A/C-only unit?
    No. In cooling mode it's just an air conditioner.

    #1 What is a fairly typical return air grill versus
    supply register temp difference in HEAT mode?
    In A/C mode, with newer (better airlfow) installations,
    14 degrees is typically what I see.
    This is called the temperature rise or alternately the delta T. In heating mode a hp's delta T will drop as the outdoor ambient temperature drops and/or as frost accumulates on the condenser coil, and is also highly dependent upon indoor air flow. It isn't a good gauge of system performance unless you have some performance data on hand to compare it to and know within reason how many cfm the blower is pushing. In general it runs higher than the cooling delta T, since there is no latent load in heating mode.

    #2 Does gauge behavior vary with heat pumps?
    In cooling, I was seeing my suction side go WAY down before
    creeping back to normal. I was thinking maybe
    the check valves take a bit of time to close off
    or something, or should gauge behavior be identical?
    And fluttering, my suction gauge fluttered about five-plus psi
    for about five seconds before dropping. I have never seen
    that in A/C-only units.
    This is behavior that will vary from one system to another and occurs in both heating and cooling modes, and can also be dependent upon the indoor and outdoor conditions, system condition, refrigerant charge level, etc.,. IOW, it means nothing to me without a slew of other data.

    #3 In cooler, maybe 45 degree weather, does the
    TXV for heating almost immediately frost or could that
    point to a problem?
    That also depends upon a number of factors. What it means is that the saturated temperature of the refrigerant leaving the TXV is below freezing. That could be normal depending upon conditions, or it could be a sign of a low charge, restriction, or liquid refrigerant piled up in the accumulator. Again this is something that means nothing without some extra data.

    #4 Not quite on topic, but do the test terminals on
    defrost boards have some DEFINITE way of working?
    I rarely find manuals with units, and am always leery
    (more scared) about jumpering test terminals. Do you
    always jump test to common or force defrost to common
    or force defrost to test? Are test terminals typically
    tolerant of being jumpered to ground or 24V, regardless
    of what they are SUPPOSED to be jumpered to?
    There's no standard, each one is different. Find the literature and familiarize yourself with the methods most used by the various manufacturers. Yes you can fry the board with a misplaced jumper. It won't happen every time but in the off chance that it will it's best not to randomly connect jumpers. On some boards the procedure will be obvious, on others it won't.

    #5 From the very vague instructional articles I've read,
    check valves seem to be mysteriously built into TXV's
    and the like. But I'm thinking they are actually very separate
    piping coming off both ends of the TXV. Am I wrong or
    am I right?
    Some check valves are external and some are internal. Just depends upon what the engineers decided to do. Internal check valves are much more common.

    Any other bits of enlightenment are welcome. When I
    am actually working with a troubled unit, I tend to forget
    every bit of basic theory about them. Stuff I read on here
    tends to stick better.

    Really, I want generalities, if they can be relied upon.
    If there are none, then that would be useful too. I mean,
    should I be looking into truck driving if I meet up with too
    many heat pumps? The bad ones are kicking my head.
    There are seasoned techs who have trouble with heat pumps in heating mode. It's a constant topic on this forum because there are so many different approaches used. The manufacturers for the most part don't provide charging data for heat mode and many will instruct you to weigh in the charge if you're in doubt. That can be very expensive for the customer, and in most cases it isn't called for either. Research some of the threads on this site pertaining to heat pumps. It'll come to you little by little and with experience your confidence will grow.

  3. #3
    Join Date
    Nov 2012
    Location
    Tahlequah OK
    Posts
    131
    I think you need to look into truck driving and leave the heat pumps to professionals. You said yourself and I quote "should I be looking into truck driving if I meet up with too many heat pumps." I've never met up with a bad heat pump. I have seen lots of heat pumps with personal problems but nothing I couldn't deal with.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,924
    Indoor air delta will vary with the outdoor temp, and efficiency of the heat pump.

    Not unusual for a heat pump to give a little gauge flutter when you switch it from heating to cooling mode.

    Can't check how well a heat pump cools when its cold outside any better then you can a straight A/C.
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  5. #5
    Join Date
    Sep 2012
    Location
    Missouri
    Posts
    64
    From what i have seen when OAT is above 40 you will see frost at the TEV at the outside unit. When I am working on HP's the first thing i do is call them outside coil (evaporator) and indoor coil (condenser). this cuts down on the confusion. as far as the test pins, always jumper from test pin to test pin. never jump test pins to ground or to 24v.

  6. #6
    Join Date
    May 2011
    Location
    Ripley, WV
    Posts
    1,161
    I would talk to my supply houses and get some literature on the units they sell, carrier, RE Michael etc.

  7. #7
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,068
    Look in the PRO section of H-talk... the open forums are restricted as to how much tech talk we are allowed to post... I would start in Pro residential forum, then look at Educational forum.

    As noted above HP's kick lots of skilled guys butts... they are non-intuitive to figure out. If it were me... I would do a boat-load of reading and study (both H-talk and as suggested supplier's literature)... then fiddle with them until you figure them out. And do not be surprised or frustrated if a bunch of them kick your butt also... this business takes time to learn.

    Couple of things I see on HP's:
    *Airflow across the indoor coil is usually not adequate... inadequate ductwork (especially lacking return and lacking air filtration)
    *Units need to be CLEAN to work properly... this means indoor and outdoor coils, filters, etc
    *Charge is critical... usually uses less juice in heat than cool mode... again indoor airflow is critical
    *RV valves tend to stick
    *TXV bypass valves will sometimes stick
    *And I have serviced a boatload of HP's where the T-stat wiring is wrong when I arrive... not sure why... however I always check the low volts wiring if anything does not work as it should.
    That should be enough to seriously confuse anyone...

    One more thing: There are few real 'general rules'... we need to KNOW what and why we are doing what we do. Education, education, education... then more education. And then some more education... because you are not through learning until you die...
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  8. #8
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,836
    I agree with everything hvacr medic said. Once you work on enough heat pumps there's really nothing to it, and a heat pump IS an air conditioner and technically a gas furnace is an air conditioner bc it conditions the air inside the structure to be comfortable for a human body.

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