Air Condition Unit

[10forty2]

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.

[10forty2]

dougrainer wrote:
Page 11. Doug

http://bryantrv.com/docs2/docs/cccir.pdf

Well ****.... guess I'll be going back up on the roof......:S

[mchero]

Just what I Thought! After replacing many roof A/C units I did not think that was supposed to be jammed into the fins.

Thanks Doug!

[dougrainer]

Page 11. Doug

http://bryantrv.com/docs2/docs/cccir.pdf

[10forty2]

mchero wrote:
That clip looks like it should clip to a copper pipe on the evaporator coil, not push into the fins.

Perhaps Doug can chime in here with his thoughts.

Totally lunched on that possibility when I was in there, but I don't remember the wires being long enough to reach the sides of the coil and the indentions on the fins were a perfect fit for the clip, so I assumed it just pushed in there. Hopefully this placement and the popsicle stick fasteners will work just as well! 🙂

[mchero]

That clip looks like it should clip to a copper pipe on the evaporator coil, not push into the fins.

Perhaps Doug can chime in here with his thoughts.

[Mr_Mark1]

10forty2

A good MacGyver move!

MM.

[10forty2]

Think I figured out the photo thing...let's see if it works....

Sensor not connected:
Click For Full-Size Image

Sensor pushed into fins:
Click For Full-Size Image

Sensor secured with popsicle sticks:
Click For Full-Size Image

[10forty2]

**UPDATE** - Finally had time to get up on the roof yesterday and pop the cover on the A/C units. The offending unit's coil fins were remarkable clean, but sure enough, the freeze sensor was dangling loose, not making contact with the fins at all. This one is a round sensor about the size of a quarter with a small clip that just pushes into the fins....I have pictures, but no way to post them. It simply would not stay put and I didn't want to ruin all the fins by trying different spots....SOooooo....wooden popsicle sticks to the rescue!! I was able to wedge the end of a couple of sticks between the plastic condensate tray and the sensor to get a snug fit that should stay put until I take it off, instead of it falling off during transit. I vacuumed the fins on both coils as well as all the leaves and stuff that had gotten inside through the gills. Then went back to the bedroom unit and did the same. That sensor was still inplace and operating fine...it was more like a temperature probe on the end of a wire that was shoved into the fins instead of a round sensor.

So my first assumption was correct, in that the unit froze up, but that was because of the freeze sensor not being in its proper place! If I can find a way to post pictures, I'll do that for everyone's future reference!

Thanks for all the replies!

[dougrainer]

vjstangelo wrote:
Sorry, I should clarify my comment. My current RV is a Winnie, the prior was a TT with a Coleman Mach 13.5 AC with controls on the unit. For that unit, the temp controller was a dial on the AC which sets the point at which the compressor will cycle off. This type of unit uses a probe (or thermocouple) that senses the evaporator coil dry bulb temperature. If the dial is set too low, the evaporator coil will get to a temperature below 32F hence the coil will build up ice. If that happens, the airflow will diminish as ice builds up on the evaporator coil fins.

I am in agreement with Effy in that a 13.5 BTUH unit will theoretically generate 13.5 BTU of cooling when the compressor is activated. The wall thermostat, or cooling temperature dial on panel mounted unit only turns the compressor on and off.

The danger of running the unit (compressor energized) with an iced over evaporator coil is that this could allow liquid refrigerant to pass from the evaporator to the compressor through the suction side hose/pipe and destroy the compressor (which is only designed to compress gas, not liquid which is incompressible).

To the OP, if the unit is no longer cooling the compressor could be toast due to liquid getting into the suction line when the coil was frozen and the compressor running.

Lets clarify with correct statements
1. The roof mounted controls, the Temp sensor does NOT sense the Evap temp. That Thermocoupler sensor senses ONLY the return air thru the Air filter. These type units can and do freeze up if on LO Cool and the Tstat is set to max cool. Rarely will they freeze if set to max cool and run on HI cool.
2. WALL tstat units have 2 sensors, NOT just the wall tstat. The wall tstat tells the AC what temp it wants. The 2nd Sensor is the FREEZE sensor installed in the evap fins. This freeze sensor will NOT allow the evap to freeze, PERIOD. IF you have this type system and the unit does freeze, FIX the sensor problem, but don't state that it is normal, because it is NOT. Both the wall Tstat AND the Freeze sensor will turn the compressor OFF. Doug

[mchero]

damntough wrote:
Our Newmar had the exact same problem. Turns out the front unit was previously replaced. The new unit was installed without the foam gasket that separates the return air from the conditioned air. Most of the air just kept recirculating through the unit without ever going into the coach. I hope this helps.

BINGO!!!

I replaced a number of roof A/C units this last winter in Quartzsite and was AMAZED at the CRAPPY job of PROPERLY sealed return and supply ducts!!!!!
EDIT
After posting I pulled the cover on my rear A/C. It is just an intake duct. I pulled the cover over the supply plenum, it forces the conditioned air thru both front and rear ducts. Took a flash light, stuck it up the intake and shined it around the seal between the divider. Looking from the output side I foun a number of gaps! Spent the last 30 plus minutes removing, cleaning and reassembling the assembly. The hardest part was sealing with the aluminum tape. Man it's hard to peel that backing off!

Tomorrow I will do the same to the forward A/C.

[vjstangelo]

Sorry, I should clarify my comment. My current RV is a Winnie, the prior was a TT with a Coleman Mach 13.5 AC with controls on the unit. For that unit, the temp controller was a dial on the AC which sets the point at which the compressor will cycle off. This type of unit uses a probe (or thermocouple) that senses the evaporator coil dry bulb temperature. If the dial is set too low, the evaporator coil will get to a temperature below 32F hence the coil will build up ice. If that happens, the airflow will diminish as ice builds up on the evaporator coil fins.

I am in agreement with Effy in that a 13.5 BTUH unit will theoretically generate 13.5 BTU of cooling when the compressor is activated. The wall thermostat, or cooling temperature dial on panel mounted unit only turns the compressor on and off.

The danger of running the unit (compressor energized) with an iced over evaporator coil is that this could allow liquid refrigerant to pass from the evaporator to the compressor through the suction side hose/pipe and destroy the compressor (which is only designed to compress gas, not liquid which is incompressible).

To the OP, if the unit is no longer cooling the compressor could be toast due to liquid getting into the suction line when the coil was frozen and the compressor running.

[crasster]

Try some usual maint things such as spraying off the coils, cleaning filters, and getting circulation. Next it may need freon. That should be enough a/c for that coach.

[10forty2]

Thanks for your ideas everyone, and thanks for the technical info Doug Rainer!! The unit in question is NOT the original unit, so there may well be a missing or misplaced gasket causing reduced airflow. I'll get up on the roof in a few days when I have time and then report back on what I find.

[Effy]

dougrainer wrote:

vjstangelo wrote:

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.

Effy is absolutely right. I can speak from experience as my DW once did the same on our 13.5 BTU unit. It was going to be over 100F one day in Denver and she set the tstat to very low temp. Since the compressor was not able to cycle off and defrost, the evaporator iced up even though the temp was hot outside with almost no cooling airflow coming out of the duct

I raised the temp so that the compressor cycled off and the evaporator ice melted. Told her not to lower less than 70F and no more problems.

Absolute rubbish. From your sig, you have a Winne. Wall Tstat RV AC Units have a FREEZE THERMISTER, which will NOT allow the evap to freeze regardless of anything else. IF your evap indeed iced up, you have a operational problem with the Freeze Thermister. FIX your problems. Don't post that some things are normal because YOU experienced a similar result. Doug

Yeah I am not too sure what it had to do with my comment. Mine was simply stating that adjusting the stat lower does not make it work harder and that it's likely low on Freon or air is restricted.