JC2
Mo
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Joined: 11/05/2004
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Just got back from a 1500 mile trip to a Tx Boomer rally in our recently acquired 2004 DSDP and have a couple of roof air(13.5 Duotherm ac/hp combos) questions. The front ac was set on 74 and during the weekend would run 2-2 1/2 minutes than shutdown for approx 10 minutes before starting again. There did not appear to be any direct sunlight or other external heat source(s) hitting the stat and the ceiling vents were also not directed towards the stat either. The rear ac was also set at 74 and seemed to run an awfull long time before shutting down. The ceiling vents direction was checked and the temp sensor on the wall was checked for crud build up and to see if it had fallen behind the wall. I have yet to take the top covers off and check but would dirty fins on top of the unit cause these problems. The stat is the 5 button type. I remotely remember a thread somewhere about the ballast in florescent lights possibly interfering with stat operation but don't remember if it was on this forum or another.
2004 Newmar DSDP 4015,370hp Cummins ISL,Spartan MM Chassis,2008 Saturn Vue,FMCA #402879,NKK 19776
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donn0128
Pronounced Ore-gun
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Joined: 04/21/2005
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Start/stop cycling is extremely hard on AC compressors. That one was IMHO short cycling. maybe because the thermostat is inaccurate, or possibly some other reasons. In any case it is not a good thing to have happening. First,check to see if there was any cold air blowing on the thermostat. Then,if this is one of the factory thermostats, I would consider replacing it with a better quality product.
Donn,Lorri,Max (The Rescued Lab)
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JC2
Mo
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randrx2 wrote:Was the temperature on the thermostat getting down to 74F in that 2.5 minutes? How hot was it outside? Was the outside temperature high enough that you needed 2 ACs running? It may be an issue of too much air conditioning capacity for a small space. This can cause your short cycling.
The outside temps were between 80-85 so (2) airs running might have overkill but wanted to give it a test as we just got this unit about 3 weeks ago. I haven't checked the ceiling vent temps yet but they felt cool enough to me. We used the ac some before the trip and don't recall the cycling problem until the trip.
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randrx2
Newport News, VA
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Joined: 03/26/2005
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Was the temperature on the thermostat getting down to 74F in that 2.5 minutes? How hot was it outside? Was the outside temperature high enough that you needed 2 ACs running? It may be an issue of too much air conditioning capacity for a small space. This can cause your short cycling.
When someone says, "I'm not book smart, I'm street smart." All I hear is, "I'm not real smart, I'm imaginary smart."
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dougrainer
Carrolton, Texas
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HOW do you know the front unit is cooling??????? From your description, the front AC is NOT running long enough to cool. There is a 2 minute 45 second delay between Compressor starts and your front compressor is either bad or the Start capacitor is bad. Your REAR AC is running longer because it is the ONLY AC cooling your unit. Doug
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JC2
Mo
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donn0128 wrote:Start/stop cycling is extremely hard on AC compressors. That one was IMHO short cycling. maybe because the thermostat is inaccurate, or possibly some other reasons. In any case it is not a good thing to have happening. First,check to see if there was any cold air blowing on the thermostat. Then,if this is one of the factory thermostats, I would consider replacing it with a better quality product.
All of the ceiling vents are aimed away from the stat and the air from the vents is cold but haven't checked with a thermometer yet.
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dougrainer
Carrolton, Texas
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The tstat reset does NOTHING for operation issues. ALL the reset does is verify DIP switch settings on each AC control board. The AC ducting is common and BOTH AC units feed air thruout the RV. The fact that it shuts down after 2 to 3 minutes shows a defective compressor. You don't state for sure that the COMPRESSOR is running during that time. Do you HEAR the compressor running or do you hear it attempt to start and then kick out. You are correct as Dometic Capacitors rarely fail. The norm is the Compressor failing. BUT, In even 10 minutes of running there is NO WAY that the roof unit could get enough cool air to blow on the tstat to short cycle. Doug
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JC2
Mo
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dougrainer wrote:HOW do you know the front unit is cooling??????? From your description, the front AC is NOT running long enough to cool. There is a 2 minute 45 second delay between Compressor starts and your front compressor is either bad or the Start capacitor is bad. Your REAR AC is running longer because it is the ONLY AC cooling your unit. Doug
Pryor to this trip, the ac's were used at home and seemed to be cycling correct at about the same temps as we encountered in Tx. I'm going to put a stat in the ceiling vents and check the air coming out of them even thought they seem cool enough, and pull the cover off the roof unit and make sure everything is clean up there. I won't be surprised if there're not as the dealer didn't do a number of things that I asked pryor to delivery. I've not ever had a capacitor go bad but I know they do. I'll keep pluggin away until I find the cause(s).
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JC2
Mo
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JC2 wrote:dougrainer wrote:HOW do you know the front unit is cooling??????? From your description, the front AC is NOT running long enough to cool. There is a 2 minute 45 second delay between Compressor starts and your front compressor is either bad or the Start capacitor is bad. Your REAR AC is running longer because it is the ONLY AC cooling your unit. Doug
Pryor to this trip, the ac's were used at home and seemed to be cycling correct at about the same temps as we encountered in Tx. I'm going to put a stat in the ceiling vents and check the air coming out of them even thought they seem cool enough, and pull the cover off the roof unit and make sure everything is clean up there. I won't be surprised if there're not as the dealer didn't do a number of things that I asked pryor to delivery. I've not ever had a capacitor go bad but I know they do. I'll keep pluggin away until I find the cause(s).
I might even try a reset on the stat.
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randrx2
Newport News, VA
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The simple check is to run just the one AC that is short cycling and see if it happens with it being the only AC trying to cool the coach.
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