Roof A/C Question July 15, 2022, 06:43:34 pm The A/C is original but has had little use. I cleaned both evaporator and condenser coils although both appeared to be very clean. The removable filters are clean. Right now the rig is parked next to my house and is exposed to very high ambient temps, up to 106 or so. Anyhow, I am running the A/C constantly (all glass has Reflectix). For much of the day, the A/C cools well but when the temperature creeps up into the upper 90s and lower 100s, the compressor shuts down while the fan continues to blow. Our other rigs had two A/Cs, one 15,000 and one 13.5. When it got this hot I would usually run both but I never had this problem before. Is is freezing up or what? Thanks.jor
Re: Roof A/C Question Reply #1 – July 15, 2022, 06:58:21 pm Hi JOR; not freezing up unless the air coming out is below about 45 degrees. If any air is coming out, then it isn't freezing. The compressor motor is shutting off to protect itself. Check the input voltage, shore power, and if it is 120 VAC or higher, then still check the voltage getting to the A/C compressor motor. There might be a test point inside the underneath in the motorhome cover. Do this if you are comfortable with DMM test leads and high voltages. RonB
Re: Roof A/C Question Reply #2 – July 15, 2022, 07:10:07 pm The compressor has a thermal overheat switch attached to the outside that shuts the compressor off when it gets too hot.Either your compressor is overheating (not good) or the switch is out of calibration and is shutting off at too low a temperature.. Our 2003 roof A/C's temp switch was bad from the Factory, it was a challenge to get it replaced under warranty.The A/C's compressor should continue working in 100+ degree weather, our LD's A/C has run every summer for twenty years in very hot conditions. If you can find a service manual for your A/C, it may have the specification of the compressor's thermal cutoff, something that can be checked with an infrared thermometer. It should also list the amperage used by the A/C, if pulling over the rated draw, the compressor may be failing.I'm putting my money on a bad thermal switch...if you can find one with the right temperature rating. The thermal switch in our LD has a proprietary part number and could not be cross-referenced with an off-the-shelf switch. The part had to come from Dometic. Maybe things are different today.Larry 2 Likes
Re: Roof A/C Question Reply #3 – July 16, 2022, 10:46:23 am I think this is just a standard run of the mill 13.5 Dometic of that era. 520316 is the model number. QuoteCheck the input voltageCould be the issue although it has not been in the past. I'm doing measurements today. e.g. My first reading this morning at the A/C showed 120 at rest and 115 running. However, yesterday, in the heat of the afternoon, the voltage in the rig's outlets was 111. (hadn't checked at the A/C at that point). We are on a major electric service but our voltage tends to drop in the afternoon and we have a number of outages. Quotehe thermal switch in our LD has a proprietary part number and could not be cross-referenced with an off-the-shelf switch. Happen to have a photo or part number for the one you found?Where is this switch? I don't see anything on or near the compressor. I found the installation manual online but don't see any reference to a thermal switch. It's cooling nicely right now.Thanks to you both.jor
Re: Roof A/C Question Reply #4 – July 16, 2022, 11:18:43 am Hi JOR; The motor windings are copper, and increases resistance with heat. This reduces the amount of current that can flow, reducing efficiency. Copper is also heavy and expensive, so for a rooftop A/C it is minimized as much as possible. I'm sure the temperatures inside the motor can be as much as 200 degrees and maybe higher before the protective switch operates. Not a good idea to melt down surrounding plastics, or catch on fire. Motor winding insulation is likely to be very high temp polyamide. I found this switch: Dometic 3100250.301 A/C Overload Protector and it might be this one. Not sure where it would be located. A measurement of 111 VAC at the rigs inside outlets might be much lower at the compressor motor. Combine the high heat with constant running and a marginal voltage, and the switch may be fine. Just doing its job. RonB
Re: Roof A/C Question Reply #5 – July 16, 2022, 12:01:32 pm Quote from: jor - July 16, 2022, 10:46:23 amMy first reading this morning at the A/C showed 120 at rest and 115 running. However, yesterday, in the heat of the afternoon, the voltage in the rig's outlets was 111. (hadn't checked at the A/C at that point). We are on a major electric service but our voltage tends to drop in the afternoon and we have a number of outages. The lower voltage on a hot summer afternoon is common, 111 volts is nothing to be worried about, yesterday it dropped here to 106 and our LD's A/C ran fine as usual.The thermal overheat switch on our A/C is the round thing about the size of a quarter, with two wires, it clips onto the compressor, It doesn't look like much but is needed to keep the compressor from overheating.Without doing a diagnostic on it, it's tough to say what is wrong. The fact that it runs normally, except on very hot days, does point to the thermal switch as being the possible cause of the A/C cutting out.If you have the tool, check the amperage draw, it may be excessive.Larry
Re: Roof A/C Question Reply #6 – July 16, 2022, 04:34:21 pm I've seen many overloads go bad, It'll be under a plastic cap on the top of the compressor. They are easy to get apart somewhat harder to put back together. You said you cleaned the condenser, did you wash it or blow it out? Either is good but if you just dusted it off it will probably need more attention. If the hot condenser is air restricted at all, it has to be able to move freely.Jon
Re: Roof A/C Question Reply #7 – July 16, 2022, 04:41:03 pm Quotecleaned the condenser, did you wash it or blow it out?I washed both the condenser and evap coils. They are very clean. Thanks for the tip on the location of the overload switch/ thermal. I'll head topside in the morning (too hot now) and get that baby out. I'll replace it. So far today the A/C is doing a great job. My voltage at the unit has not fallen below 113 and it's blowing nice and cold with 101 outside temp and 76 in the rig. It's losing ground but trying hard.jor 2 Likes
Re: Roof A/C Question Reply #8 – July 17, 2022, 11:22:15 am QuoteI'll head topside in the morning (too hot now) and get that baby out. I'll replace it. Best laid plans... Topside I went and uncovered the gizmo on top of the compressor but I did not find a removable overload protector. As you can see in the photo there is a barrel-like component inserted into the compressor but as far as I could tell (gentle pliars) it is not removable. I suppose it is an integrated overload protector? So... I think I'm out of ideas on this thing.Yesterday, it performed well all day until it hit about 105. Then the compressor shut down and the fan continued to blow ambient air. The voltage at that time at the unit was 117. Anyhow, we don't plan to camp anywhere where it's 105 degrees so I guess you could say the A/C is good to go! (a bit chagrined but hopeful as ever!!!)jor
Re: Roof A/C Question Reply #9 – July 17, 2022, 01:08:33 pm Hi Jor; Did you undo that nut in the center there in your picture. That apparently is what is holding that "overload protector" in. The parts list calls it that and they are available in many places. That means they fail a lot. It would help a lot if I knew exactly what model you have. Dometic Duotherm Brisk Air II. Is it the Penguin. Is it a heat pump model? (not to be confused with the add on heat strip). Part number of the A/C, and model. It could also be some other part interfering with the operation of the compressor, such as a temperature related failure of the starting capacitor. Although the symptoms fit more for the overtemp protector. This site was interesting: RV Camper Boat A/C Hard Start Kit Dometic Penguin 3311883000 Air Conditioner... RonB
Re: Roof A/C Question Reply #10 – July 17, 2022, 01:39:27 pm Dometic Model Number: 520316.506E. It's the original so whatever LD was installing on the 09 models. I think it's a DuoTherm although it is the only component I don't have the documentation for.QuoteDid you undo that nut in the center there in your picture. Yea. See second photo. If that is it, it looks to be integrated with the compressor. jor
Re: Roof A/C Question Reply #11 – July 17, 2022, 04:38:41 pm That is not the motor overload.... Those are your compressor motor terminals. Usually the overload is under the second round space. Yours has either an internal overload embedded in the windings or something external maybe on the discharge line. The small hot one leaving the compressor. I need to go back to your pictures. It could be on the line coming out of the top of the compressor going to the condenser and I don't see it. They might have something in with the start components. The hard start components Ron linked to, have built in overloads and the one on the compressor would be eliminated. Jon
Re: Roof A/C Question Reply #12 – July 17, 2022, 06:09:30 pm Man, you'd think finding this thing would be easy. There must be many thousands of these old Dometics on RV roofs. I have not been able to find a drawing that shows the overload switch, however. I'm going to take another look in there and see if I can find something somewhere that looks like an overload switch mañana in the morning. Thanks.Oh, one other thing. I was out there today working on something when the A/C started blowing warm air. I turned down the thermostat setting to 64 and the compressor kicked on. It blew cold for awhile. jor
Re: Roof A/C Question Reply #13 – July 17, 2022, 08:37:06 pm Maybe a person should be looking elsewhere. Is the tstat electronic. Maybe you should jumper the tstat and see if it stays running.Jon
Re: Roof A/C Question Reply #14 – July 17, 2022, 09:41:52 pm QuoteMaybe you should jumper the tstat and see if it stays running.Hmmmm... Now that's something I hadn't thought of. I'll give it a try! It's the standard 5-button Duo-Therm. The only problem I've had with those things is the buttons get cranky but who knows! Can't complain though. This a/c deal is the only thing I've found on this new to me rig that isn't working right.jor 1 Likes
Re: Roof A/C Question Reply #15 – July 19, 2022, 04:15:12 pm QuoteMaybe a person should be looking elsewhere. Is the tstat electronic. Maybe you should jumper the tstat and see if it stays running.Well, now. Yesterday I intended to jump it as suggested. However, this is an electronic therostat (Duo Therm Comfort Center) so no wires. Anyhow, I found instructions on how to reset it and did so. Two things changed:1. The A/C ran all day blowing cold (got up to 103 or so);2. When I turned it on, the fan started right away. Before this, there was a significant delay before the fan engaged.Keeping my fingers crossed. Thanks.jor
Re: Roof A/C Question Reply #16 – July 19, 2022, 09:04:34 pm I know relays and capacitors and stuff but you have a t stat that I know zero about. Electronics are good but they sometimes they need a little love. Reset might of done it.Jon
Re: Roof A/C Question Reply #17 – July 22, 2022, 03:06:07 pm QuoteMaybe a person should be looking elsewhere.OP here. All fixed and blowin' cold. JonS came up with the solution and the cost was within reason - free. After searching for capacitors, thermistors and thermal overload switches, I simply reset the Dometic 5-button and whadayaknow, success! Thanks to all. I now know a lot more about that roof a/c!jor 1 Likes
Re: Roof A/C Question Reply #18 – July 22, 2022, 04:29:17 pm Good to hear Jor! These newer digital thermostats no longer simply open and close contacts to control heat and ac functions. A serial stream of data is now used I believe over just one wire. Makes things easier for a builder install but not necessarily so for us owners who want to do a repair. Nice that reset is available and that it worked for you.
Re: Roof A/C Question Reply #19 – July 22, 2022, 05:05:24 pm Quote from: jor - July 19, 2022, 04:15:12 pmWell, now. Yesterday I intended to jump it as suggested. However, this is an electronic therostat (Duo Therm Comfort Center) so no wires. Anyhow, I found instructions on how to reset it and did so. Two things changed:1. The A/C ran all day blowing cold (got up to 103 or so);2. When I turned it on, the fan started right away. Before this, there was a significant delay before the fan engaged.Keeping my fingers crossed. Thanks.jorCan you share the manual or explain how to do the reset? Glad it worked!
Re: Roof A/C Question Reply #20 – July 22, 2022, 10:54:24 pm QuoteCan you share the manual or explain how to do the reset? Glad it worked! Reset Thermostat (DuoTherm Comfort Control)When you are going to do this action, remember that all previous program memory will be erased and the control will reset to factory settings of 72 degrees F for cool and 68 degrees F for heat.1. Turn the device on and the light and annunciator data are there. If they are, move on to step 2 and if they aren’t, consult your manual section 5.1. 2. Press the mode button to activate the annunciator light.3. Then, at the same time, press the up and down buttons and hold.4. Now while the up and down buttons are still pressed, use another finger to press the mode button and release it right away. You only need to press that button once at this time.5. When releasing the mode button you can release the up and down buttons.6. Press the mode button again. The light should go out and the mode should say ‘off’. If it doesn’t do the same steps all over again.7. Test the system to make sure the system reset and is working.8. When you see it is working right, re-program your settings to the levels you want. 3 Likes
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Topic: Roof A/C Question (Read 455 times)
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