15K rooftop Unit. Went on a overnight concert trip this weekend and camped in a grass parking lot. It was exceptionally hot/humid for this time of year and we were running both A/C units as hard as they could go....set at 64 to get the coach to cool down. The one in front is the 15K unit...the bedroom is a 13.5K unit. Bedroom unit was cooling fine with plenty of air coming through the ceiling ducts. BUT....the front unit was barely moving air through SOME of the ceiling ducts with fan set on high. What air was moving was fairly cool feeling, but not what it has been in the past, and again, very little air movement even though we could hear the fan running and it was set on high. Is something maybe blocking the ducts or did it freeze up from all the humidity? I've never tried to pull the cover on the unit and see what's in there. I'll go back out today and see it it seems to be any better after being off for a couple of days.

It sounds like it just iced up, which could be from a low Freon level or from exceptionally high humidity. Of course your rear AC operated fine in the same humidity so I am guessing that there is probably a problem with your front unit that caused it to ice up. You may want to pull the top cover and clean everything and remove the ceiling cover and make sure that all of the duct connections are sealed.

Is it low on Freon? Why did you set to 64? Did you really want the temp to reach 64? Because turning it down further than the desired temp does not make it work any harder or faster. A thermostat is not an accelerator. If you want 72, setting it to 64 won't make it cool to 72 any faster than actually setting it to 72. It does not run cooler the lower you set it. If it froze up then it's low on Freon (or whatever they put in them these days). Were you plugged in shore power and getting the right power to it? Is the unit clean? If it can't breathe right it can't cool efficiently.

Effy wrote:Is it low on Freon? Why did you set to 64? Did you really want the temp to reach 64? Because turning it down further than the desired temp does not make it work any harder or faster. A thermostat is not an accelerator. If you want 72, setting it to 64 won't make it cool to 72 any faster than actually setting it to 72. It does not run cooler the lower you set it. If it froze up then it's low on Freon (or whatever they put in them these days). Were you plugged in shore power and getting the right power to it? Is the unit clean? If it can't breathe right it can't cool efficiently.I set it to 64 because I like it cold in my RV and I wanted icicles hanging when I came back in from the hot concert....:BI do know that it doesn't cool faster set that low, but it never seems to be cool enough inside until I get the temp (according to the thermostat) down into the 60s. All window shades closed and a floor fan running. I keep my house at 68 and ceiling fans running all the time..... I haven't had a problem in the past three years with the A/C units, but this time it just wasn't moving the air.When I was up on the roof cleaning it, although I didn't remove the cover, I did visually look for tree debris and anything else I could see through the gills. All appeard to be good from the outside.

rgatijnet1 wrote:It sounds like it just iced up, which could be from a low Freon level or from exceptionally high humidity. I will add to this.. I've seen clogged filters restrict air flow as well. But conitions that can add up to icing areNO FROST SENSOR or frost sensor mis-placed.. I've not seen this personally but have read about it.. The frost sensor is a Temperature probe stuck in the evaporator (cold) coils.Low Freon (Seen many times)Low air flow (Clogged filters seen once, or fan on low)and overly high humidity (Again I've not PERSONALLY seen this)Also though it is tempting to set the things at a lower temp to "Cool faster" it's a myth that it will do so, set to 70 or 72 and let it work, setting it in the 60's won't cool any fasterSame (With reversed nubmers) applys to heating as well, IT will heat just as fast at 73 as it will at 93.

10forty2, the covers come off so easily on the roof-top units. It won't take but a couple a seconds to remove the four screws and lift the cover off. I'm not sure you could see everything with the cover on. Take the cover off and clean everything. There are some foam and rubber pieces that may have come loose that might need to be repositioned.Of course you will need to check/clean the inside ceiling filter. Good luck,MM.

Air Condition Unit | Good Sam Community

rgatijnet1
Explorer III
May 01, 2017
It sounds like it just iced up, which could be from a low Freon level or from exceptionally high humidity. Of course your rear AC operated fine in the same humidity so I am guessing that there is probably a problem with your front unit that caused it to ice up. You may want to pull the top cover and clean everything and remove the ceiling cover and make sure that all of the duct connections are sealed.
Effy
Explorer II
May 01, 2017
Is it low on Freon? Why did you set to 64? Did you really want the temp to reach 64? Because turning it down further than the desired temp does not make it work any harder or faster. A thermostat is not an accelerator. If you want 72, setting it to 64 won't make it cool to 72 any faster than actually setting it to 72. It does not run cooler the lower you set it. If it froze up then it's low on Freon (or whatever they put in them these days). Were you plugged in shore power and getting the right power to it? Is the unit clean? If it can't breathe right it can't cool efficiently.
10forty2
Explorer
May 01, 2017
Effy wrote:
Is it low on Freon? Why did you set to 64? Did you really want the temp to reach 64? Because turning it down further than the desired temp does not make it work any harder or faster. A thermostat is not an accelerator. If you want 72, setting it to 64 won't make it cool to 72 any faster than actually setting it to 72. It does not run cooler the lower you set it. If it froze up then it's low on Freon (or whatever they put in them these days). Were you plugged in shore power and getting the right power to it? Is the unit clean? If it can't breathe right it can't cool efficiently.

I set it to 64 because I like it cold in my RV and I wanted icicles hanging when I came back in from the hot concert....:B

I do know that it doesn't cool faster set that low, but it never seems to be cool enough inside until I get the temp (according to the thermostat) down into the 60s. All window shades closed and a floor fan running. I keep my house at 68 and ceiling fans running all the time..... I haven't had a problem in the past three years with the A/C units, but this time it just wasn't moving the air.

When I was up on the roof cleaning it, although I didn't remove the cover, I did visually look for tree debris and anything else I could see through the gills. All appeard to be good from the outside.
wa8yxm
Explorer III
May 01, 2017
rgatijnet1 wrote:
It sounds like it just iced up, which could be from a low Freon level or from exceptionally high humidity.

I will add to this.. I've seen clogged filters restrict air flow as well. But conitions that can add up to icing are

NO FROST SENSOR or frost sensor mis-placed.. I've not seen this personally but have read about it.. The frost sensor is a Temperature probe stuck in the evaporator (cold) coils.

Low Freon (Seen many times)
Low air flow (Clogged filters seen once, or fan on low)
and overly high humidity (Again I've not PERSONALLY seen this)

Also though it is tempting to set the things at a lower temp to "Cool faster" it's a myth that it will do so, set to 70 or 72 and let it work, setting it in the 60's won't cool any faster

Same (With reversed nubmers) applys to heating as well, IT will heat just as fast at 73 as it will at 93.
Mr_Mark1
Explorer
May 01, 2017
10forty2, the covers come off so easily on the roof-top units. It won't take but a couple a seconds to remove the four screws and lift the cover off.

I'm not sure you could see everything with the cover on. Take the cover off and clean everything. There are some foam and rubber pieces that may have come loose that might need to be repositioned.

Of course you will need to check/clean the inside ceiling filter.

Good luck,
MM.
Effy
Explorer II
May 01, 2017
10forty2 wrote:
Effy wrote:
Is it low on Freon? Why did you set to 64? Did you really want the temp to reach 64? Because turning it down further than the desired temp does not make it work any harder or faster. A thermostat is not an accelerator. If you want 72, setting it to 64 won't make it cool to 72 any faster than actually setting it to 72. It does not run cooler the lower you set it. If it froze up then it's low on Freon (or whatever they put in them these days). Were you plugged in shore power and getting the right power to it? Is the unit clean? If it can't breathe right it can't cool efficiently.

I set it to 64 because I like it cold in my RV and I wanted icicles hanging when I came back in from the hot concert....:B

I do know that it doesn't cool faster set that low, but it never seems to be cool enough inside until I get the temp (according to the thermostat) down into the 60s. All window shades closed and a floor fan running. I keep my house at 68 and ceiling fans running all the time..... I haven't had a problem in the past three years with the A/C units, but this time it just wasn't moving the air.

When I was up on the roof cleaning it, although I didn't remove the cover, I did visually look for tree debris and anything else I could see through the gills. All appeard to be good from the outside.

I hear ya. I know our thermostat in our RV is really inaccurate. Says it's 70 when it' actually like 73-74.
Fleetwood_Coupl
Explorer
May 01, 2017
I little trick a long time RVer told me to help was to set the rear unit to a colder temp and set fan to low, then set the front to desired temp and auto. The duct work is connected and the rear unit will blow the colder air from the back to the front to help cool the larger space. If possible close the door between the main and bed room. It worked good for me when it got hot in southern CA before I could head north.
10forty2
Explorer
May 01, 2017
So is the duct system just a plenum space above the ceiling or is it actual flexible ducting?
AJR
Explorer
May 01, 2017
Remove the return air filter on the ceiling. With a good flashlight see if you can see the cooling coils up there. When I did this there was no question that ice had formed. While looking up there I saw what looked like a cooking thermometer dangling on a wire. After I thawed the ice off the coils I could see where that sensor was just stuck into the cooling fins and held in place by friction. I just stuck the sensor back into the fins and never had another problem with the unit. The sensor turns off the compressor if it detects ice on the fins. The fan melts the ice and the compressor starts back up.
Effy
Explorer II
May 01, 2017
10forty2 wrote:
So is the duct system just a plenum space above the ceiling or is it actual flexible ducting?

In most RV's it's just channels cut in the Styrofoam insulation in the roof. No real duct work at all.

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