Roof Air Conditioner unit icing up

[Hahn007]

1985 chieftain with Coleman roof mounted air conditioner.  Evaporator ices up after running for several hours. Anybody else experiencing this?

Thanks in advance,
Chris

[2nstoys]

Very common problem. Check for air leaks between the air intake and outlet. Make sure that it is sealed up from each other. That wll cause icing. Also running on low fan for long periods will also do it.

[Lefty]

A dirty condenser or evaporator will restrict the air flow thru the fins, causing icing. You can remove the interior cover to inspect it for dust and dirt buildup, as well as climb on the roof and remove the cover to inspect the upper sections.
I use an air compressor to blow mine out before the start of each season. Be sure to clean the interior foam pre-filters often too. I find mine need cleaning about once a month when used heavily. If you cook a lot inside, or smoke, it will require cleaning more often.

[Hahn007]

Thanks for the reply.
Not exactly sure what you mean by air leaks between the air intake and outlet.
Are you referring to the intake inside the coach, through the evaporator, and out through the registers?
Where would one start looking for leaks in this area?

Running fan on low or temp on low?

Thanks again,
Chris

[Rickf1985]

Check the foam seals around the outlets, if the cold air is leaking by and into the warm air return which is right next to the outlets it will freeze. this is a common problem with the older units and an easy one to fix with weatherstripping.

[Hahn007]

Thanks I will check that this weekend when I have the RV out camping.

A dirty condenser or evaporator will restrict the air flow thru the fins, causing icing. You can remove the interior cover to inspect it for dust and dirt buildup, as well as climb on the roof and remove the cover to inspect the upper sections.I use an air compressor to blow mine out before the start of each season. Be sure to clean the interior foam pre-filters often too. I find mine need cleaning about once a month when used heavily. If you cook a lot inside, or smoke, it will require cleaning more often.

Good points.I cleaned the condenser really good when I got the RV.I didn't however clean the evaporator as I couldn't see a very good way to do it without disassembling the sealed sheet metal enclosure when accessed from the roof.Hmmmm compressed air from the inside on the evaporator sounds like a good idea, I will have to give that a try.Thanks again,Chris

[JerryP]

If it was serviced recently, or before you bought it, this same issue is also caused by too much refridgerant

[lngfish]

Usually by removing a couple dozen screws you can get to clean the evaporator after the outside cover is removed. Just did both of mine. Just sprayed inlet of Evap with some degreaser , let is soak and lighly hose off. Secure power, keep clear of capacitors up there. Put rag in duck up there . Check drains.

[lngfish]

My fan had 2 holes for 3 in 1 oil. So I squirted some in and spun fan. One motor for Evap and Condenser. Motor should spin freely and not drag.

[DRMousseau]

Long periods of disuse and oversight can quite problematic for mobile air conditioners. How many of us find the need in early summer while driving on the highway only to find the AC isn't gonna work when we wanted.

A periodic full cycling of AC units during the long cool fall/winter/spring season, can do much to prevent AC problems and even detect some servicing needs BEFORE the busy summer season. I cycle mobile car and truck units monthly, and household units a couple times during winter and have been laughed at dearly,... till early summer.

I really hate removing shrouds and covers for cleaning, but I've experienced that icing issue too many times and it's ALWAYS too dang hot to messin' with when you have problems. You can't neglect regular and preventative maintenance without consequences that sometimes can be serious.

Clean the condenser and evaporator good, inspect seals, filters, drainage ports, and check for adequate air circulation in ALL areas (especially important in humid conditions). If outside temps are cooler than inside, it will also cause freezing on the indoor coils. This something I watch for during those "off-season" cycles I run. I don't want everything iced up ALL winter! I run the units jus enough to circulate and run fans to begin cooling. Freezing can damage your system no differently than your plumbing and batteries if not addressed immediately. I can dislocate or damage lines, cause corrosion and leaks and more.

IF, under normal conditions, and you have done ALL the above, and it's still freezing,... then you'll likely need the services of a professional. It may be low on refrigerant due to pin leakage ("Worked fine for a few days after servicing, then froze up again!), or it may be a plugged or faulty expansion valve or low pressure switch, or even a damaged line somewhere. Solving these issues are usually beyond the capabilities of most folks.

Keeping units clean can much for preventing pin leaks and the corrosion that often causes them, and prolong the useful life of your AC unit.

[Lefty]

My fan had 2 holes for 3 in 1 oil. So I squirted some in and spun fan. One motor for Evap and Condenser. Motor should spin freely and not drag.

Excellent point. The older units typically used an oil bath lubrication system for the fans.. there will be a small drip cup at the bearing where you are supposed to add a few drops of machine oil periodically. I think they recommended doing it twice a year, but not positive.