Roof AC Freezing

[karenandcollins]

The copper tubing on our class "A" rooftop Dometic Duo Therm A/C is icing up between the motor & front of the unit, while the tubing from the motor to the back does not ice up. I can't see any blockage anywhere. After running for awhile it leaks water into the unit. We were told awhile ago if we run the fan on high, which we do, we shouldn't have freezing problems. Any suggestions?

[wolfe10]

Steps to reduce freeze up:

1. Run fan on high.

2. Turn thermostat a little warmer.

3. Be sure to keep the air return filter clean/replaced.

4. Clean the EVAPORATOR COILS with a good commercial evaporator cleaner from any HVAC store and many box stores. Particularly critical if A/C is operated in humid climates. This needs to be done once a year in humid climates and/or when you get that musty smell when first turning on the A/C.

5. Check ducting in ducted A/C's to insure that cold air can not recirculate back into the return side of the unit.

Brett

[cwschnepf]

When your evaporator coil ices over it is usually a sign the unit is not picking up enough heat from your camper. First check would be to pull down the filter at the ceiling and let it run for a few hours. If it works wash out or replace the filter. You didn't say the age of your camper but there is a possibility the gaskets directing the air through the coil may be failing or not placed properly to do the job. Second the fan may be slipping on the shaft. You need a long allen wrench to tighten the set screw in the fan collar. I hope this helps you..

[cobrafang61]

Heat pump and AC coils must be chemically cleaned annually or a huge loss of efficiency/capacity results. HVAC/R supply houses sell condenser/evaporator coil cleaner, its a mild acid liquid that once sprayed into the coil, foams up, pushing debris from inside the rows of fins as well as stripping off any smoke, grease,oils, dirt, dust that accumulates rather quickly upon the coils. As in the heat mode the outdoor coils air conditioning the outdoors the outdoor coil sweats, like a beer can will, thus the dust/dirt that accumulates is turned to muck, and adheres to the backside of the outdoor coil since the fan motor slings the condensate upon the coil via splash ring. Without a cleaning, no unit will work well after awhile.

As to charging the unit, as mentioned its a sealed system, which many units are, freezers, refrigerators,dehumidifiers, wine chillers, window ac units etc. There are no schrader ports to service them, however you can apply a "piercing valve which goes on the :low side" which is usually around 70 psi in ac mode, in heat mode it will be 270 or so, so you need to remove the piercing valve once you reclaim the refrigerant, if any, and silver solder a schrader port into the low side, a high side isn't required. This is the correct way to add a service port, if it were just AC, the piercing valves are OK if just subjected to 50-70 lbs of pressure, but heat pumps reverse so the low side is a high side in heat mode, so piercing valves are for reclaiming refrigerant and adding a schrader port properly. If you need to add refrigerant, you are leaking, which may be small and a annual recharge will get by.

If not they sell sealers that actually do work well there days for $50. But given that the new units $800 and labors about $106.50 per hr and parts markups 100% to 500% depending on parts cost/size, a compressor may be 100% marked up, refrigerant 500%, $75 a lb for R22, 3 hours labor to clean and evacuate and recharge will be $400-$500 easily, not an economically viable alternative, especially considering your compressor and components are old too, you may not be happy with a repaired old unit too? They do get tired, losing volumetric efficiency /compression as cars will.

I read a "Master RV technician" here saying the systems in a vacuum, not correct, its positively charged with 70psi on the low side while running and 270 on the high side approximately, even off its whatever ambient correlates to on the temperature pressure chart for that refrigerant, if it has any liquid refrigerant is will be at X temp at X pressure according to the heat its subjected to parked, not running, at no time is it ever in a vacuum except when preparing it to be charged!