Dometic Penguin Roof-Top Heat Pump

[duffel]

I have a 2005 Holiday Rambler Admiral 34SBD with a Dometic Penguin 13,500 btu heat pump forward and an 11,000 btu a/c unit aft, both units controlled by a 5-button Dometic comfort control center with remote sensors. When stationary (the coach operating on 50 amp shore power or generator) and both roof top units in cooling mode, the forward unit fan will stop after about 20 minutes of operation.

However, the compressor will continue to run until it stops from overheating or until I manually turn it off at the comfort control center. The aft unit operates normally. When underway at highway speed operating on generator with both roof top units in cooling mode, the forward unit will, on most occasions, operate normally so long as the fan is in the "low" position. If the fan is in the "high" or "auto" position the fan will stop after about 20 minutes of operation. Again, the aft unit operates normally. I'm reasonably confident that the forward unit fan motor is not the problem. I've run the forward unit in "fan only" mode for several days at a stretch without a glitch. Has anyone else ever experienced the foregoing difficulty? If so, what was the cause of the problem?

I welcome any and all comments, suggestions and/or recommendations aimed at a solution.

Thanks in advance for the help.

[dickandlois]

Duffel,

Welcome to FMCA!

Have you taken the time to remove the cover and clean the Evaporator fins?

Dirt build up or items can block the fee flow of air through the coil.

This leads to thermal build up and loose of cooling.

Rich.

[dalltop]

When this front fan stops you need to inspect the unit to be sure it is not iced up and physically stopping the fan motor from turning. If the unit is freezing up the fan motor may still be turning but not pushing air across the coils.

[duffel]

Rich & Dalltop:

Thanks for the replies. The entire roof-top unit is clean inside and out. The fins are clean and straight. There is no evidence of the unit icing up. I've gone through all the troubleshooting procedures described in the Dometic service manuals (available on-line thanks to Bryant RV www.bryantrv.com), and still can't find the cause of the problem. Logic tells me that the cause is something electrical or electronic because of the intermittent nature of the problem. If it was mechanical in nature (fan blade blocked, seized fan motor, etc.) the cause would be readily apparent. If the unit was icing up, there would be evidence of ice/water present. Does anyone know if it is possible for a run capacitor to have intermittent function? Specifically, those terminals on the capacitor that are connected to the fan, fail (open?) when the capacitor is energized for a period of time, while the terminals connected to the compressor don't fail and work normally. This thing really has me puzzled.

[dickandlois]

Dalltop,

With the fan turning freely, clean evaporator and surrounding area clean that kinda removes the mechanical items out of the equation. Like you mentioned.

Caps can break down when hot! I keep going back to the compressor, BUT have to remind myself that it will keep running.

So I'm back to the starter and the caps. Kind of have to eliminate the starter, because it always starts when on low speed.

Always has a problem on high speed correct?

That would leave the high speed winding in the motor or the run cap. So I would change the run cap and see what happens.

Should it still quit on high then one has to lean towards the motor and an issue when it heats up.

Second question, when the fan stops on high, Will it start right up as soon as you set it to low speed?

There is a clue to the problem in there somewhere, the trick is to find it. !!!! LOL

Rich.

[duffel]

Hello Rich:

When the motor stops and I manually turn off/stop the unit at the Dometic comfort control center, it takes a few minutes before I can re-start the unit. I am reliably informed that the delay is normal and is a function of the control center's internal protocol. Be that as it may, when the unit is in the "fan only" mode, the fan will run without a problem for days on high or low - depending on the setting that I've chosen. Thus, I don't believe that the fan is problem. If the fan was to be the problem, it is logical that the fan would stop after 20 minutes or so even if the roof-top unit isn't in the "cooling" mode. You may have a point about the run capacitor possibly breaking down when it gets hot. I may have a spare and will see if replacing the existing capacitor solves the problem. Thanks.

Duffel

[dickandlois]

Duffel,

Sounds like a plan, remember that the fan draws air in over the evaporator coil and the air temperature would be higher due to the heating affect. You did mention that the fan would run longer while driving do the road. To me that could mean that the air entering the AC unit through the side vent could be having a cooling affect on the hotter air being drawn in through the evaporator.

It will be interesting to see what effect the capacitor has on things!!

Rich.

[ronjudi]

Sounds like thermal overload in fan which then cuts fan off. Fan motors are protected and when they get hot from overload the fan motor protector opens up to protect the motor. Compressors are also thermally protected but would not know the fan is running so would continue to run until it also overheats and cycles the overload protector on the compressor.

Measure fan current with a clamp on Amp meter and if it is too high find out why. Perhaps there is shorted winding in fan or more probably a bearing that is failing causing excessive mechanical load on the rotation of the fan.

Old posting so too late but I would guess the fan motor needed replacement.

Ron