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Topic: Roof Heat Pump Problem (Read 558 times) previous topic - next topic

Roof Heat Pump Problem

Our rear Penguin heat pump initially comes on, runs about 15 seconds then goes to a higher than high blower speed for about 15 seconds, then shuts off, and after the two minute delay it repeats the same sequence. After doing this three times it will continue to run normally the fourth time.

New start and run capacitors last winter,  but wife says it's been doing since before then.

Ideas anyone?

Re: Roof Heat Pump Problem

Reply #1 –
    Quote from: Traveling Man –
    Our rear Penguin heat pump initially comes on, runs about 15 seconds then goes to a higher than high blower speed for about 15 seconds, then shuts off, and after the two minute delay it repeats the same sequence. After doing this three times it will run normally the fourth time.

    New start and run capacitors last winter,  but wife says it's been doing since before then.

    Ideas anyone?
    T-Man,
    More likely than not, your AC is just Freezing Up.  If the AC speeds up several times, mostly when it is first started, the refrigerant is starting to frost the condenser fins, the freeze sensor increases the fan speed to increase the airflow and remove the frost.  But, if it frosts up too much, it shuts the AC down completely.  A sure indication is if when the AC is shut off, a bit of water sometimes drips from the intake filter grill area. 

    What can cause the frost/freezing?
      • RV's are smaller volume than a house and are (relatively) much tighter/less moisture absorbant. 
      • Unless you take steps to reduce them, moisture and humidity tend to be higher inside an RV than in a house.
      • Vapors from cooking, bathing and even breath accumulate more and that moist air frosts easily when an AC is initially trying to cool down the space.
        4. RV AC's have more cooling capacity per unit volume of cooled space and are therefore capable of freezing up the evaporator fins more readily than a normal house air conditioning system would be.

      What can you do?
        • Clean intake filters often.
        • Dry the filters before returning them to service.
        • Run fan speed at least one speed higher than normal until the space is cooled down (moves air through the evaporator unit faster to keep it from frosting up).
        • Set your thermostat at a REASONABLE, MODERATE setting. If you set it too far to cool, the compressor does not get to cycle (too far from setpoint), so frost never gets a chance to be shed — Frost just builds up until the freeze sensor (first) increases the fan speed and then (second, if ultimately unsuccessful) shuts off the AC.  Set the thermostat just a degree or two less than the inside temperature and once that is achieved move down another two or three degrees.  Setting the thermostat too far in the cool direction causes the compressor to run continuously and an AC that is operating well will freeze the incoming moist air!
        • Turn the fan switch to ON in a higher speed than normal, rather than AUTO, which helps to disperse the moisture more rapidly.
        • Always open a roof vent (fan ON) or two when taking showers and cooking to expel added moisture as much as possible.
        • Check condenser fins (on the roof, under the shroud) at least twice a year for debris buildup, clean the fins, "card" them to straighten them as necessary and whatever else is necessary to restore and improve air flow.
        [/list]

        There are other things that your freezing up might be, but 95% of the time its one or more of the above and just operator misunderstanding of how an RV's AC works (they work the same as a house but the RV "house" has different volume and moisture characteristics).

        What other things might be causing the freezing up — the other 5% possibility?
          • Split plenum
          • bad fan/run capacitor
          • grounded or shorted motor
          • low freon level
          [/list]

          Try the above possibilities first though, because it will save you bunch in parts, labor and frustration.

          HTH,
          Neal[/list][/list]
          The selected media item is not currently available.
          Neal (& Brenda) Pillsbury
          '02 U320 SPEC, 4200, DGFE, Build #5984
          '04 Gold Wing
          '07 Featherlite 24'
          '14 Jeep Grand Cherokee Summit
          MC #14494
          Exeter, NH & LaBelle FL
          Quality makes the Heart Soar long after Price is Forgotten

          Re: Roof Heat Pump Problem

          Reply #2 –
          Thanks Neal.

          I'm aware of some of the info you just posted concerning frost but don't understand how that can occur within 15-30 seconds after initial start-up??

          I have had the units drip water as you described but only after they ran continuously for a long time.

          Also, I can't change the fan speed when it is running in COOL mode, only when the FAN ONLY mode is selected.

          Re: Roof Heat Pump Problem

          Reply #3 –
          Very weird indeed, doesn't sound like a condenser fan failure or a compressor going off on thermal overload. The fact that it starts and runs on the fourth attempt is very strange. Is air coming out the grilles on the first few attempts. Something wirng  heating up and finally making good contact may be a culprit. If a plastic evaporator fan set screw was loolse it might be possible for it to engage after awhile of spinning on the shaft and heating up. Idk
          Old Phart Phred, EIEIO
          89 GV ored 36' #3405 300 hp cat 3208 ATAAC side radiator, mountain tamer exhaust brake

          Re: Roof Heat Pump Problem

          Reply #6 –
          Quote from: stump –
          I would suspect the potential relay.

          Looking at my wiring diagram I see a PTCR
          located between the start and run capacitors...... would that be it? 

          Also,  regarding my initial post I was mistaken in that the fan runs on low and high as it should, and when first trying to start it runs on low, then goes to high, not higher than high.

          Re: Roof Heat Pump Problem

          Reply #7 –
          Yes.
          If the relay failed it will keep the start winding energized, the compressor will cut out on thermal overload as it cools it will start again and keep repeating. It can also at times work as it is supposed to wich sounds like what yours is doing.
          These replacements have more terminals than yours probably does but you just use the ones you need. This is what I put on mine when it went bad.
          SUPR Universal Potential Relay - CSH Electric Motor Supply
          91 GV U300 Unihome 40' Build 3811
          6V92TA Detroit