A/C built-in thermostat question - A/C not cycling often

[DazedNConfused]

Good morning. Camped over the weekend in probably the warmest non-shade temps we've done so far -- around 90-92 degrees. I have a 40-foot 5th wheel with twin A/Cs -- a 15K in the main living space and a 13.5K in the front bedroom.

The main A/C worked like a champ. Ran lots all weekend, but produced nice cool air. My concern is the 13.5K unit. It runs and cools fine when the compressor is cycled...but the issue I am seeing is that the compressor doesn't cycle as much as I'd like for it to. I experimented a bunch this weekend varying the fan speed between low, med, and high....and adjusting the dial-thermostat that's built into the return/blower housing. At the hottest part of the day, the main unit was doing all it could...but I wanted to supplement with the bedroom unit...however it would only run for a minute or two...and then cycle off again. It would cycle from time to time...but maybe only 4 times per hour (I didn't time it).

My camper is stored indoors...and I inspected the coil and such by removing the outside cover...and there wasn't anything obvious going on, nothing looked very dirty, etc.

I did read that some folks say the built-in thermostat being so close to the moving air can cause the compressor to cycle off. Curious what people's thoughts are on this. If this is reasonable or expected, can I wire in a wall-mount thermostat so it's farther away from the unit and bypass the built-in one?

So for the most part the main A/C was doing the bulk of the cooling. As such, it would cycle at 74 or above...but would run non-stop below 74. I was happy with that...but would be happier if I could get the second unit to help share the load more effectively.

Of note, I have a Progressive Industries surge protector installed with a remote display...so I can tell by looking at the second 50-amp leg when the bedroom A/C is just blowing air vs. the compressor also running -- usually a 5amp draw vs. 16 or so amps.

Thanks,
DNC

[time2roll]

Here is the product manual:

http://www.dometic.com/4051e767-809b-45df-a50f-d8f28e443826.fodoc

Page 15 shows a simple thermostat to close the compressor circuit.
Page 12 says thermostat samples inlet temperature.

Probably need an HVAC thermometer to verify the inlet temperature and thermostat are operating as expected.
Dial should cover about 65 to 90 degrees. (pg 12)

[DazedNConfused]

smkettner wrote:
Can just crank the bedroom thermostat to max cold... or is it?

Any chance you are running on 30 amp supply with an EMS load shedding the bedroom air?

I worked my way up to max cold...but that didn't seem to matter. I'm certainly no electrician, but I was plugged into 50 amps. I had enough voltage on each of the two legs...and when the compressor was running, it was demanding almost 20 amps from that leg -- so I believe there was ample power for the unit.

[time2roll]

Can just crank the bedroom thermostat to max cold... or is it?

Any chance you are running on 30 amp supply with an EMS load shedding the bedroom air?

[DazedNConfused]

The A/C unit is a Dometic and here is the information from the sticker:

MFG# 457915.711CO

Serial No. 30524009

Prod No. 991762978

It's a 13,500 BTU unit

Thanks for everyone's input.

[TXiceman]

More than likely, the problem is the bedroom unit is somewhat confined. The thermostat will simply start and stop the compressor based on what it is sensing.

You can add a fan or two to help get air out of the bedroom. Mount one up high blowing into the bedroom and set one on the floor to blow air out of the bedroom. This will help the circulation a bunch.

ken

[DazedNConfused]

wa8yxm wrote:

wa8yxm wrote:
Two thoughts.. You said you removed the outer cover, Did you also remove the cover over the condenser coils? This is where it really gets gunked up, in the "Backside" (Fan side) of the condenser coils.

Page 2. HOW HOT WAS IT (outside the RV that is) the hotter the more the compressor runs.

Finally a quick check you can run that does not even require a ladder!!

Using a clamp on AC ammeter, Carefully CAUTION DANGEROUS VOLTAGES EXIST open the breaker panel and identify the wire that runs to the air conditioner you are worried about,, Fit meter over wire in the manner explained in the meter owner's manual and measure current draw. Compare to the A/C's specification lable..

Example. mine is 13.5 amps.. So if it's much less than 10, or more than 15 I have a problem. (It hit 21, the condenser was clogged)

Let it run for a while if it's normal.. (NOTE Starting (first second) may be higher) took mine a few mintues to hit 21.

On my particular rig, it was a 30-amp setup. I optioned in the 50-amp service when I optioned in the second A/C. To the best of my knowledge, not much is hanging off that second leg besides the second A/C as I never see more than an amp or two draw when reading the progressive industries meter which cycles 24/7. When the A/C is running, it jumps to about 19 amps, I think. I'd have to look again to remember. When the A/C compressor is cycled off and just the A/C blower is running, I see 5 amps of draw. Voltage on each leg was reading between 116v and 118v the whole weekend.

[DazedNConfused]

wa8yxm wrote:
Two thoughts.. You said you removed the outer cover, Did you also remove the cover over the condenser coils? This is where it really gets gunked up, in the "Backside" (Fan side) of the condenser coils.

Page 2. HOW HOT WAS IT (outside the RV that is) the hotter the more the compressor runs.

I'll admit it was a very quick inspection. I'll also admit I wasn't 100% sure what to look for...but was hoping if something at least look out of place, it would jump out at me. But this was one of those times I wasn't sure what I was looking for. I chose to spend more time with the A/C adjustments to see if I could find a pattern or t-stat position, but didn't come up with much. I would think, though, that if I maxed out the t-stat to the coldest setting...it would stay on longer than a few minutes at a time...and cycle more frequently that just a few times per hour...but I could be way off base here.

[wa8yxm]

wa8yxm wrote:
Two thoughts.. You said you removed the outer cover, Did you also remove the cover over the condenser coils? This is where it really gets gunked up, in the "Backside" (Fan side) of the condenser coils.

Page 2. HOW HOT WAS IT (outside the RV that is) the hotter the more the compressor runs.

Finally a quick check you can run that does not even require a ladder!!

Using a clamp on AC ammeter, Carefully CAUTION DANGEROUS VOLTAGES EXIST open the breaker panel and identify the wire that runs to the air conditioner you are worried about,, Fit meter over wire in the manner explained in the meter owner's manual and measure current draw. Compare to the A/C's specification lable..

Example. mine is 13.5 amps.. So if it's much less than 10, or more than 15 I have a problem. (It hit 21, the condenser was clogged)

Let it run for a while if it's normal.. (NOTE Starting (first second) may be higher) took mine a few mintues to hit 21.

[wa8yxm]

Two thoughts.. You said you removed the outer cover, Did you also remove the cover over the condenser coils? This is where it really gets gunked up, in the "Backside" (Fan side) of the condenser coils.

Page 2. HOW HOT WAS IT (outside the RV that is) the hotter the more the compressor runs.

[DazedNConfused]

tpi wrote:
It sounds like it runs so little the stat could actually be faulty.

There's a couple guys who really know their stuff on here regarding AC units. If you could get the model info, they probably could tell you exactly what to look for.

When the unit was new, it would cycle once....then it would never cycle again. Dealer replaced the t-stat. It's possible it's been this way since then...but this was the first full-sun warm weather trip we've had. Up until now we've chosen cgs that have had full shade in the summer....so even when it was hot out, the camper stayed much cooler. Make/model info forthcoming.

[tpi]

It sounds like it runs so little the stat could actually be faulty.

There's a couple guys who really know their stuff on here regarding AC units. If you could get the model info, they probably could tell you exactly what to look for.

[DazedNConfused]

tpi wrote:
Is the bedroom AC located in a confined space and air rapidly cools and kicks off the thermostat? Somehow recirculating cold air into the thermostat space? If so a remote thermostat could help. If not I'd suspect the thermostat being defective or the probe located improperly. The fact it only runs four times per hour could indicate that. Best to post the make/model and some of the forum experts on AC could chime in.

I had similar situation in my house where thermostat was much to close to forced air register. The air conditioning would cycle off much too soon-and the solution was relocating the thermostat.

Yeah...normally at night we'll close the sliding door to the bedroom and then it would certainly be more confined. This weekend I had the bedroom door open..and was hoping air would move to the main cabin. Maybe a small box fan on the steps leading into my bedroom would help. I'll get the make and model this evening and post. I'm not sure exactly what a properly placed probe would look like...but i'll read to see where it's supposed to be and will drop the inside cover and "inspect".

On the main unit, an inspection showed there was a taping issue between the plenum and the duct-work...so I sealed that up and greatly increased airflow to the vents.

[tpi]

Is the bedroom AC located in a confined space and air rapidly cools and kicks off the thermostat? Somehow recirculating cold air into the thermostat space? If so a remote thermostat could help. If not I'd suspect the thermostat being defective or the probe located improperly. The fact it only runs four times per hour could indicate that. Best to post the make/model and some of the forum experts on AC could chime in.

I had similar situation in my house where thermostat was much to close to forced air register. The air conditioning would cycle off much too soon-and the solution was relocating the thermostat.