A/C Freezing Up

[MrFixit454]

New RV, 32' 15k Dometic ducted w/ remote control T-stat. I have known for years about A/C freeze ups on low fan but I am experiencing freezup on high fan as well, when ducted. Less freeze up when dropping the air straight down. I took all sorts of temp readings in the RV over the weekend of which I don't have right now. As for the weather, 90 deg. outside (31% humidity, dew pt. 52deg.) I can't seem to get the compressor to cycle at 76 deg. inside. When I click it up a couple of notches, I hear the compress shut off and I hear the ice falling into fan I guess and a ton of water dumps off the roof from the gutter as it melts. While cleaing the roof last night, I noticed brown streaks running from the A/C in the rubber roof that won't clean up. This is 4 month old trailer and every other streak washes off OK. I will bring it to the dealer as I am under warranty but I want to do my homework first. The shielding in the airbox was not done right so return air was being sucked back in. I sealed it all off when I first bought the trailer as I had little flow when I did my own PDI. I searched other threads and it sounds like it might be low on freon?? This means they have to add a service port which might present problems later??
Thanks in advance.
Ramon.

[MrFixit454]

New RV, 32' 15k Dometic ducted w/ remote control T-stat. I have known for years about A/C freeze ups on low fan but I am experiencing freezup on high fan as well, when ducted. Less freeze up when dropping the air straight down. I took all sorts of temp readings in the RV over the weekend of which I don't have right now. As for the weather, 90 deg. outside (31% humidity, dew pt. 52deg.) I can't seem to get the compressor to cycle at 76 deg. inside. When I click it up a couple of notches, I hear the compress shut off and I hear the ice falling into fan I guess and a ton of water dumps off the roof from the gutter as it melts. While cleaing the roof last night, I noticed brown streaks running from the A/C in the rubber roof that won't clean up. This is 4 month old trailer and every other streak washes off OK. I will bring it to the dealer as I am under warranty but I want to do my homework first. The shielding in the airbox was not done right so return air was being sucked back in. I sealed it all off when I first bought the trailer as I had little flow when I did my own PDI. I searched other threads and it sounds like it might be low on freon?? This means they have to add a service port which might present problems later??
Thanks in advance.
Ramon.

[TXiceman]

Make sure you air bypasses (that you closed) have not opened up again. Also, are you keeping the air filter clean? Start the unit and after about 10 minutes of operation, get a temperature reading of the air coming out of the duct closest to the unit. Next get a reading of the air that is going into the unit. The air off should be about 20 degrees colder than the inlet air. If it is more than 20 degrees, you mostly likely have a low flow problem or low refrigerant.

90% of the problems with an RV A/C are not low refrigerant. In order to check the unit, the dealer will need to put in a clamp on temporary connection on the compressor suction and discharge. These do not seal very well and will leak. After it is checked, a decent tech will recover the refrigerant from the unit and solder in permenate Schrader connections (like bike tube tires)and reepair any leaks. Then they have to evacuate the unit (pull it into a vacuum to get the moisture out) and finally recharge the unit.

Best to let the dealer handle it. They may want to just replace the unit.

Ken

[MrFixit454]

Thanks Ken,
I used the alum. foil hvac tape to seal everything up as the metal divider was cut too short. The foam seal was 1/2" from the top of the air box. I also made better transitions into the duct work with this tape. Since this is new, the filter had a 1/2 hour of use before this trip and I can't see any dust like my prev. trailers. So hopeully everything is good there. Here are my numbers, although this is not after 10 min., this is after several hours at about 3 in the afternoon.

Outside temp. 89 deg.
Inside temp. near return, 75 deg.
return air near closest duct, 50 deg. on high fan, 46. deg on low fan.

Tstat set at 73 deg. If I set tstat to 77 deg, compressor kicks off and minutes later the waterfall outside begins.
I have seen those clamp-on units before and maybe the people who had problems never had them welded up like you said. I'll see what my dealer says. The wife was laughing at me all weekend making all these readings.. it's the test engineer in me I guess.
P.S. after I sealed off the intake and return air and got good flow, a heard a noise running down the duct and it was a cut out from one of the registers (a circle) that they never removed. Guess I need to scope the rest of the ducts!

[TXiceman]

Sounds like you have a problem with the air flow, low refrigerant or several other things. You will need to get an amp probe on the unit and see where it is running and if the motor is loaded or not. Can't do much more long-distance testing, so you need to get to a tech.

Running the unit on low fan is asking for problems. I wish the manufacturers would eliminate the low speed switch.


Goot luck,
Ken

[MrFixit454]

Thanks again for all your input. I dropped it off at the dealer this morning and we will see what they say. I just want to be educated when they inform me of what they did (or didn't do), then I can tell them to try what you suggest. I have all the installation instructions and user manuals for my model. What I find intersting (havning owned 3 5th wheels) is that some manufactueres don't follow the installation requirements. Number of ducts, reisters, size of ducts etc. My A/C is near the rear and I have 2 ducts on one run and 5 on the other. I need to measure duct size a surface area of all the openings. I'll let you know what they come up with.

[MrFixit454]

I picked up the trailer at the dealers today and as I expected, they said it did not freeze up on them in 3 hours of operation. Maybe this was not enough time. I guess I will have to do more of my own testing and examination. I need to check the freeze sensor to see if it is making proper contact and actually working. My BIL has a scope and we are going to scan the ducts for problems as well. This might take a few weeks since my trailer is in storage. I'll get back to you when I find something out.

[Bounder Ernie]

Try leaving one of the roof vents open about half way. When I had my TT I had a freezing up problem, I left one of the roof vents open to release the warm air and moisture. Solved my problem. Ernie

[MrFixit454]

Funny you should say this.. my sister has the exact same trailer and hers was not freezing up. Ther difference was she had the main door open in the ealry day and early evening while running her A/C and she was not having my problem. I have always been a "Close everything" when running A/C. I'll try it out next time we are out.
Thanks