First off, glad to have found this site as it appears to have lots of good information from fellow RV'ers. We are currently living in our Forest River Wildcat 5th wheel for going on a year now (new home being built). Ever since buying this camper new in '16 we've had issues with the AC, the thing seems to start/stop alot while it's cooling, I realize it should "shift" the fan to Hi if it's too far out of range on the thermostat but it doesn't seem to do that very often, it will shut the fan off (not compressor) several times in the course of a few minutes or it will just run flawless all day, never know. Well, earlier this year the thing wouldn't come on at all and I just figure it bit the bullet, so I bought a new one and installed it, guess what... same thing but at least it ran. A few weeks go by and it refuses to start again, T-stat is set as 72 and it's almost 90 in here, I call the dealership and they tell me that more thank likely either my T-stat or control box is bad so I drive 2 hours to get a new control box and T-stat, install it and and same thing. So now I'm thinking I have a good AC unit thrown into the dump pit and something else is the problem since I just spent $1600 on a new AC/Control box/T-stat. What else is there besides wire running from the AC to the T-stat.??Right now we are having to basically reset the thermostat each time it shuts down, it will run and satisfy the thermostat and when it shuts down it will not restart without doing that, which really sucks at night!!! During the day while it's so hot it just runs all day.I'm at a loss!! I'll try and search the forum for more tips.

I am not familiar with Dometic units, I have 2 Coleman units on my coach, controlled by a single tstat. If your tstat controls the unit thru a data wire vs the normal 12v Y1 wire, then interference could be the cause. I had pursued my issues for almost two months before I tracked the culprit to an ac to dc 12v wall transformer. Once I replaced the transformer units have been trouble free. I would start by turning off all your 120v breakers except for the main and the a/c unit. See if the unit will run normally. If it does, then I would begin turning on the other breakers one at a time, monitoring the unit. My issue was found when I turned on one of the general receptacle breakers on the inverter sub panel, which happened to control all my entertainment systems in the coach. The transformer powered my HDMI to CAT5 conversion module and was hard to locate. This may or may not be a solution for your system, but I would find the schematics for your tstat to see if it controls the unit thru a data wire.

1. Need Model of AC2. need P/n of Control board3. need model of tstat. Is the tstat a single zone LCD square tstat? 3 wires going to wall tstat?4. Is the Freeze thermister installed in the evaporator? 5. Ducted AC system?6. Separation plenum installed between the air intake(filter) and cold exhaust plenum?7. TOP mount AC unit or you have the 4 bolts from inside the RV? Doug

Inquire at your RV park or campground (managers/owners) about a mobile RV repairman with electrical/AC experience. A Google search may also help you find a dude that knows RV AC and electrical systems in your general location area. Inquiry phone calls may also be necessary in addition to email contact.I was always very lucky in that my Dometic AC would freeze me out even in the high heat of Texas summers.

I would not run with the fan on low. Ice up is a common occurrence with low fan speed. I’ve never seen a unit that changes speeds on its own

jkwilson wrote:I would not run with the fan on low. Ice up is a common occurrence with low fan speed. I’ve never seen a unit that changes speeds on its ownDometic on Auto will go from Hi to Lo or Hi to med to lo fan speed depending on the model of the Top AC unit. Doug

First Post, Out of Frustration over Dometic AC | Good Sam Community

wa8yxm
Explorer III
Aug 07, 2023
Jsledder wrote:

Running the fan on high can be counter-intuitive since the compressor shuts off during the satisfaction of the T-stat and the fan continues to run and bring in the hot/humid outside air which then causes the dehumidifier to run which produces heat... so on and so on.

Well, if your A/C is like a 1970s model. It might have a Fresh air intake, but modern ones do not. The outside and inside air flows are 100% separated. It does not draw outside air into the RV unless there is a defect as the two sides are sealed from each other. Outside air is ued ONLY to cool the condenser. It's not brought in..

Same with most window A/C's.. back in the 80's they had "Fresh air" doors (and/or exhaust doors) you could open.... Today they do not.

For the very reason you cite in fact.

I've been on the roof and taken the cover off multiple makes of A/C's and there is only a very tiny path (The Drip Tray) that's common to both sides and it's usually water locked if the unit has run for any period of time.
jimh406
Explorer III
Aug 07, 2023
There are some options for you to help make the AC run cooler. Those include adding some sun deflection/insulation. Even changing the direction pointed can make a difference.

Things we've found to work include sunscreen awnings, reflective in the windows/skylights or covering the skylights. You don't have to leave them in place all day, but they can do a lot to reduce the heat in the hottest part of the day.

Assuming you are an early riser, make sure you cool off the inside as much as possible.

What size 5th wheel are we talking about and what size BTU unit? I'd be surprised if one is enough unless it's really short.
jkwilson
Explorer III
Aug 07, 2023
Jsledder wrote:
wa8yxm wrote:
There are several things folks often overlook

First make sure the intake filter(s) are clean. if they are dirty air flow is reduced and some A/C's have "Frost" detectors. these detect when the evap starts to Ice up (or rather they should) and shut down the compressor... That sounds like your issue.

Second make sure the condenser (Rooftop the part that gets HOT) is clean.. For different reasons.. IF I Were making an A/C i'd include an over pressure sensor. I do not think Dometic did but that's how I'd do it.

Finally Fan on high.. Not low. Not auto Two reasons.

First.. Your problem.. Fan on high might fix

Second.. Yes I know it is noisy but it's very close to "White noise" which means your brain, given a few minutes, will filter it out.. and what's more that fan noise will cover the compressor so you won't be as annoyed by it cutting in and out be it short or long cycling (you will hear it but you might need to pay attention to do so) Also when your next site neighbors get into a knock down drag out.. You won't hear that either. (Trust me on that count... Throwing things through the window level fight and I never heard a thign).

Thanks for your feedback.
This AC being a month old is still clean and the filters get cleaned regularly, I have an air compressor close by and try to blow out each unit, along with the fridge and water heater area, monthly.
Running the fan on high can be counter-intuitive since the compressor shuts off during the satisfaction of the T-stat and the fan continues to run and bring in the hot/humid outside air which then causes the dehumidifier to run which produces heat... so on and so on. When it's really hot out we have to do that with the unit in the front, no t-stat, and the humidity gets crazy up there.

It appears that replacing this simple little therimister was the answer, thanks Doug for asking about that, it was just by happenstance that I pulled that down while looking for the model number and then it took off. Going on day 3 of the unit working the way it should, which it really never has since new.

The air conditioner fans neither bring outside air into the trailer or expel inside air out. The air paths are completely isolated. Only refrigerant passes between the inside of the trailer and the outside carrying heat to the outside.
dougrainer
Nomad
Aug 07, 2023
StirCrazy wrote:
ok so when I did my PDI walk through, the guy stressed to never run the ac in auto or with the fan set to low. So, for me it's always on hi. not saying it's your issue but could it be? Have you tried it in a different setting?

IF you have a wall tstat in an RV, the roof AC has a freeze Thermister, so the evap can NEVER freeze regardless of conditions. Roof AC's in an RV that has manual knob controls on the upper plenum, YES, do NOT run on LO as these units have NO freeze thermister. These units also have NO auto since the fan control is a manual switch. Doug
jjrbus
Explorer
Aug 07, 2023
They have been selling low quality generators and AC to RV'ers for years, it is interesting to see some of the new products coming on the market. I modded a window AC for my Toyota.

Noise, first they put a hole in the roof and then install the electric motor, fan and compressor in the hole. Simply ducting the intake and cooled air would reduce noise a lot, very inexpensive to do during construction.
StirCrazy
Moderator
Aug 07, 2023
ok so when I did my PDI walk through, the guy stressed to never run the ac in auto or with the fan set to low. So, for me it's always on hi. not saying it's your issue but could it be? Have you tried it in a different setting?
Jsledder
Explorer
Aug 07, 2023
wa8yxm wrote:
There are several things folks often overlook

First make sure the intake filter(s) are clean. if they are dirty air flow is reduced and some A/C's have "Frost" detectors. these detect when the evap starts to Ice up (or rather they should) and shut down the compressor... That sounds like your issue.

Second make sure the condenser (Rooftop the part that gets HOT) is clean.. For different reasons.. IF I Were making an A/C i'd include an over pressure sensor. I do not think Dometic did but that's how I'd do it.

Finally Fan on high.. Not low. Not auto Two reasons.

First.. Your problem.. Fan on high might fix

Second.. Yes I know it is noisy but it's very close to "White noise" which means your brain, given a few minutes, will filter it out.. and what's more that fan noise will cover the compressor so you won't be as annoyed by it cutting in and out be it short or long cycling (you will hear it but you might need to pay attention to do so) Also when your next site neighbors get into a knock down drag out.. You won't hear that either. (Trust me on that count... Throwing things through the window level fight and I never heard a thign).

Thanks for your feedback.
This AC being a month old is still clean and the filters get cleaned regularly, I have an air compressor close by and try to blow out each unit, along with the fridge and water heater area, monthly.
Running the fan on high can be counter-intuitive since the compressor shuts off during the satisfaction of the T-stat and the fan continues to run and bring in the hot/humid outside air which then causes the dehumidifier to run which produces heat... so on and so on. When it's really hot out we have to do that with the unit in the front, no t-stat, and the humidity gets crazy up there.

It appears that replacing this simple little therimister was the answer, thanks Doug for asking about that, it was just by happenstance that I pulled that down while looking for the model number and then it took off. Going on day 3 of the unit working the way it should, which it really never has since new.
Jsledder
Explorer
Aug 06, 2023
Yes it did, I installed that last night (for whatever reason I didn't when I put in the new control box) and the AC ran all by itself all night, turned on and off all on it's very own! Kind of like having a 2 year old that finally sleeps all night.
wa8yxm
Explorer III
Aug 06, 2023
There are several things folks often overlook

First make sure the intake filter(s) are clean. if they are dirty air flow is reduced and some A/C's have "Frost" detectors. these detect when the evap starts to Ice up (or rather they should) and shut down the compressor... That sounds like your issue.

Second make sure the condenser (Rooftop the part that gets HOT) is clean.. For different reasons.. IF I Were making an A/C i'd include an over pressure sensor. I do not think Dometic did but that's how I'd do it.

Finally Fan on high.. Not low. Not auto Two reasons.

First.. Your problem.. Fan on high might fix

Second.. Yes I know it is noisy but it's very close to "White noise" which means your brain, given a few minutes, will filter it out.. and what's more that fan noise will cover the compressor so you won't be as annoyed by it cutting in and out be it short or long cycling (you will hear it but you might need to pay attention to do so) Also when your next site neighbors get into a knock down drag out.. You won't hear that either. (Trust me on that count... Throwing things through the window level fight and I never heard a thign).
dougrainer
Nomad
Aug 06, 2023
Did the NEW control not come with a NEW freeze Thermister? IF not replace the freeze thermister. Doug