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campinia's avatar
campinia
Explorer
Jun 19, 2017

Coleman Mach 3 coils freezing

We tried to run our A/C for the first time this year and it would try to cool for about an hour, then the evaporator coils would be iced over and it would not cool any more. The unit is a Coleman Mach 48000 series, non-ducted. It worked fine up through last fall and we have not needed it until this last weekend. I cleaned the evaporator and condenser coils yesterday and the filters. When I first opened up the inside ceiling unit, I found that the small vinyl duct from the cold air side into the trailer had come loose enough that a little of the cold air could escape. I tightened that back up as the screws had backed out a little and then resealed with new double sided tape. I thought that would solve the problem, but it didn't. I ran for an hour yesterday and it never lowered the temps more than a few degrees inside and after about an hour, I could look up and see that the evaporator was icing up and there was no water coming off of the roof as has always been in the past. This has always been an excellent unit that would cool down our 24 foot box in about 10-15 minutes in humid 90 degree weather and then freeze us out if we let it. Yesterday was only 80 degrees and not even really very humid. I just want to know if there is anything else I should be looking for. The fans are blowing well, I cleaned the coils, and there does not seem to be any cold air leaking over to the warm side in any way. The fins on all of the coils seem to be open and in good shape. I tried it on two different days at two different camp ground power pedestals. My temperature gun showed that the air coming out of the duct yesterday was initially 69 degrees and then as it iced up it warmed up to over 70 within the hour and this was with the T-stat maxed and 79 degrees outside. This is a 2 year old trailer and A/C that have never been damaged. I find it hard to believe that it leaked refrigerant for some reason, but, I can't think of what else it would be. Any ideas would be appreciated.
  • j-d's avatar
    j-d
    Explorer II
    Jun 19, 2017
    When you cleaned, were you able to get to both sides of the Evaporator Coil, and clean the Drain Pan (and its drain holes)?

    Have you tried running it on HIGH Fan, or only Low?

    Gotta say, I don't like the 69* but I want to add that a temp gun isn't as good for measuring air temp as a thermometer is.

    Do you have a Clamp-On Ammeter? Your compressor should be marked "RLA" for Running Load Amps. If you measure the Amps at the main connection to the A/C, then find the RLA for the Fan and add that to the Compressor's RLA. If the actual Amp Draw is less than that (or grossly more than that) it's likely there's compressor trouble or a refrigerant leak.

    Do these things leak? Sure, but not all that often, and Coleman seems to be one of the tighter ones. I thought I had to replace the 1983 Coleman Mach 13500 till I cleaned it. Thing wasn't cooling, and the Evap was freezing over. After cleaning, it cooled very well again, and ran well till we sold the coach in 2008. It was then, that I picked up the "run fan on High" tip and it's really helped.

    Our present coach has Coleman Mach 15000, still running since 2002 (some years full time) with only cleaning and a new blower motor.

    Both the 13500 and the 15000 units are non-ducted. I cut intake filters from "30-day" home A/C filters and change them often. One 20x20 filter gives me two sets for the RV.
  • TenOC's avatar
    TenOC
    Nomad
    Jun 19, 2017
    As I understand, coil freezing is caused by low Freon. On my home A/C there is a thermostat located at the coils that shuts off the compress when the coils start to freeze up so they can warm up.
  • j-d's avatar
    j-d
    Explorer II
    Jun 19, 2017
    TenOC wrote:
    ...coil freezing is caused by low Freon... On my home A/C there is a thermostat located at the coils...


    Low refrigerant as a cause, is true. What happens, it there is no longer sufficient refrigerant to maintain adequate pressure in the Evaporator. What happens is, the refrigerant expands "prematurely" right where it enters the Evap. If that produces a sub-freezing temperature, frost begins there.

    Another cause is a Fouled Evaporator. Dust and Dirt reduce air flow and also insulate the coils under that layer of "stuff." Once one area freezes, that block of frost/ice expands till a big part of the evap is clogged with frost.

    Tied into all this, of course, anything else that reduces air flow (like Fan on Low not High)promotes freezing. An otherwise OK A/C can freeze on a humid day with Low Fan.

    And, so can bringing extremely humid air into the evap area in the form of an intake air leak to the outside.

    RV A/C units don't have the Freeze Sensor unless they are Ducted. The Ductless, with Fan and Temp Knobs, like mine and apparently like the one in this thread, don't have that feature.
  • campinia's avatar
    campinia
    Explorer
    Jun 19, 2017
    j-d wrote:
    When you cleaned, were you able to get to both sides of the Evaporator Coil, and clean the Drain Pan (and its drain holes)?

    Have you tried running it on HIGH Fan, or only Low?

    Gotta say, I don't like the 69* but I want to add that a temp gun isn't as good for measuring air temp as a thermometer is.

    Do you have a Clamp-On Ammeter? Your compressor should be marked "RLA" for Running Load Amps. If you measure the Amps at the main connection to the A/C, then find the RLA for the Fan and add that to the Compressor's RLA. If the actual Amp Draw is less than that (or grossly more than that) it's likely there's compressor trouble or a refrigerant leak.


    Do these things leak? Sure, but not all that often, and Coleman seems to be one of the tighter ones. I thought I had to replace the 1983 Coleman Mach 13500 till I cleaned it. Thing wasn't cooling, and the Evap was freezing over. After cleaning, it cooled very well again, and ran well till we sold the coach in 2008. It was then, that I picked up the "run fan on High" tip and it's really helped.

    Our present coach has Coleman Mach 15000, still running since 2002 (some years full time) with only cleaning and a new blower motor.

    Both the 13500 and the 15000 units are non-ducted. I cut intake filters from "30-day" home A/C filters and change them often. One 20x20 filter gives me two sets for the RV.


    I don't think I have a clamp-on ammeter any more, will have to look. I did only run it with high fan, actually, the new ones have a combination knob that is either high cool or low cool and the fan is integrated into that. We have only run on high cool. I did clean both sides of the evaporator coil, but, I did not clean the drain pain and drain holes, think I will go out and try that!
  • time2roll's avatar
    time2roll
    Nomad
    Jun 19, 2017
    Since it used to freeze you out, can you set the thermostat so the compressor barely kicks on... this should allow the compressor to cycle a bit and minimize the freeze up. Also keep the blower fan set to high continuous.

    Not really a fix but may get you through a few days to figure this out or get service.
  • Chris_Bryant's avatar
    Chris_Bryant
    Explorer II
    Jun 19, 2017
    I hate to say it, but you have checked all there is which commonly causes freeze up, so I do think you are loosing the refrigerant charge. A quick and dirty don't-ever-do-this-except-now test would be to turn it on, let it run for 10 minutes, then turn the thermostat up to shut the compressor off, then right back down to turn it back on- short cycling it. I thin the compressor will restart easily, indicating very low charge. Of course, if it doesn't start, turn the thermostat back up so it doesn't cycle on the overload.
  • campinia's avatar
    campinia
    Explorer
    Jun 22, 2017
    Thank you for the replies everyone. I found a new upper unit locally and I installed it in about an hour. It was very easy to swap them out. I had quotes of about $500 to install plus the unit cost. The soonest anyone could look at is was August and our whole summer would have been gone. No one would have wanted to go in the camper with the mid 90 temps and high humidity that we have been getting already. I still can't believe that a 2.5 year old unit went bad, but, it happens. I am now sitting here enjoying meat locker temperatures!
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jun 22, 2017
    Some folks have it made.
    With tropical conditions, I had to purchase a dehumidifier and use it in conjunction with an A/C in order to bring relative humidity down to less than sixty percent. The A/C was fighting to lower temperature from 95F to 80F. When I ran the dehumidifier the first time, the room temperature simply fell to 70F. This cycled the A/C.

    Live and learn. Condensing humidity is not friendly
  • billyboy's avatar
    billyboy
    Explorer
    Jun 22, 2017
    I think you should have bought a freeze sensor and hooked that to the evaporator coil
  • down_home's avatar
    down_home
    Explorer II
    Jun 23, 2017
    We have in the past had the coils ice up when run on low fan speed and high moisture.
    Recently we had one unit quit. Fan had to be replaced.
    Checking the vents inside it was discovered a lot of the cooled air was going right back to be cooled again due to no gasket or sealing around the intake, just pieces of fiberglass board loosely fitted. They taped it up with metal tape and no leaking back to the cooling side and early shut off, and a lot of lost cool air elsewhere.
    I going over that with the thought that, because I think it contributed greatly to the icing up under slow fan speed and high humidity, since the units were designed to function under such conditions.

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