Question about Dometic Rooftop RV Air Conditioner

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A/C switching to heat

Hi, I have a 630516 unit that will run for a short period in the A/C mode and then switch to heat. I have checked power to the reversing valve coil and have power to it. Is the problem a weak coil or do I have problems elsewhere?

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  • mechmagcn Jul 15, 2008

    After extensive troubleshooting, I figured out the problem. The coil on the reversing valve was getting hot and no longer able to hold the valve in the A/C position. After replacing this coil, the unit is working as it should.



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I have the same problem, it may cool for 1 min or 5 min then go to heat mode. Once it goes to heat mode only way to reset is to shut the AC down and let it cool. It may or amy not work the next time.

Posted on Jul 14, 2008

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Simple way to pay less bill with big comfort.
Tips for it: To get proper cold air set temp 23 degree and mode"cool". To get heat set temp 30 degree and mode in "Heat" Clean indoor and out door periodically ( Once in 4 months) Clean Air filter every fortnightly. Avoid frequent opening of the door where it's air conditioned. Avoid keep closing the doors even a/c is switch off. It helps to cool the room next times in short minutes. Use proper breaker, wiring for your air conditioner plug points. Make sure your elect meter is working properly.Check your Elect meter with 1000watts bulb for one hour. It should consume one unit only. Hope, it's helpful.

Jan 08, 2011 | Heating & Cooling

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I have an intertherm rpbmb030k combo a/c and heat. Had frion put in the unit over the summer and a new digital thermostat. Unit has worked great until we needed heat. Unit works great on aux. heat but...

Hi, if the unit had a leak in it, was the leak located and repaired? Did he check the pressures in the unit now? If it switches to the aux mode ( Heat Strips ) is normally caused when your primary unit, compressor and freon are low on charge. I would have that checked.
A/C, & Heating Contractor

Dec 03, 2010 | Intertherm P3RA-060K Air Conditioner

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No heat, no ac. Power apparently not getting where it needs to be. Checked the fuse in the unit (5amp) still good. I have non-fusable boxes located next to furnance inside (crawlspace) and outside unit....

Hi, you do have a power problem, that's for sure.If the indoor unit has a non-fused box, and condenser also, it would have to be at the main breaker. That's the only power source you have that supplies power to everything is the main breaker. If you are sure you have power to the main unit, 120 volts to the furnace, you should have a led light that's is on, and its either red or green. This will tell you there is power there. The 5 amp fuse is for the secondary control voltage, 24 volts.If you could unplug your furnace in the craw space and plug something else in to check for power, you would know for sure. You may just have a faulty thermostat. If you turn the switch, fan switch to on, it should come on. If not, you have lost power. If you have a volt meter, this would be very helpful. You could have a bad transformer, but normally the 5 amp fuse will blow to keep the transformer from blowing out. I would check the fan switch, turn it to on and see if it runs, if not, you have lost power at your indoor unit. Make sure the panel on the indoor unit is put on right, as most of them have a panel switch on the perimeter that closes when you put it on to restore power. If its not on just right, it will keep the switch open, and you will have no power, so double check that panel. Check the led light, door switch, power to the indoor unit, and let me know what you find. It should be pretty easy to find where the problem is, if you are in the heat mode. This eliminates the outdoor unit, so you will know it is the indoor unit. Please let me know and keep me posted. You will find it, its a easy fix.
A/C, & Heating Contractor

Nov 30, 2010 | Heating & Cooling

1 Answer

Heat side of heatpump is blowing a transformer when switched to heating mode.

It is either a shorted wire or a shorted component in the heat cycle wiring. The most likely is a bad reversing valve solenoid. You can use a re-settable transformer to help lower cost while troubleshooting. Remove the RV solenoid wires and set the unit for heat. If nothing blows,you will have found the problem. If it is not the RV,plug it back in and remove another low voltage wire and restart the unit. Keep doing this until the unit runs. When it runs OK,the last wire removed will go to the defective part.

Oct 04, 2009 | Ruud UAMB Air Conditioner

1 Answer

Hi, I have a wall mount midea split a/c model- MSG-36HR that will only heat. when put in cool mode it only blow's room temp air and the outdoor unit won't run. On heat mode it works normally. I have cycled...

Most heat pumps are 'fail-safe to heat'. That is: the normal position of the valve which reverses the function is in the position which provides heat. The reversing valve must be powered to switch to the cooling position.

Although the lack of valve function could be a mechanically defective reversing valve - it's more likely to be an electrical issue. Start with checking for power at the reversing valve's coil. If it's powered unpower it - you will be able to hear the reversing valve distinctively

Oct 03, 2009 | Midea Heating & Cooling

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Reversing valve not switching over to air on heat pump. compressor will come on for about 10 minutes, then shut off. Hot air comes out vent.

Look for any refrigerant leaks - no or low refrigerant can cause problems in both modes. The unit may be going off on low suction.


The unit may be stuck in the heating mode.

Make sure the system is calling for the correct mode (cooling or heating) - some systems are auto, but if you can, select cooling since that is the requested mode. Check for power at the reversing valve inside the condensing unit. If power exists, then the reversing valve is stuck. It could also be the reversing valve solenoid coil, so make sure that isn't bad. There should be a strong magnetic field at the solenoid coil.

If you can hear the reversing valve clicking (moving), check the T-stat and make sure it will switch modes. Also check the reversing valve relay (those can be located in either the indoor unit or condensing unit).

May 25, 2009 | Ruud Matching Split Air Conditioner

2 Answers

GE zoneline heat not working

You need to have some one check the continuity of the thermal fuses at the plug where it plugs into the side of the control box. It's a two pin plastic white plug with black fabric covered wires coming out of the plug, you should have about (0) resistance or maybe 1 ohm. If you have no reading at all you will have to pull the heating coils out. Not a big job but, the unit must be removed from the wall as you have to take off the long top metal plate. Remember you do this only if you have to get to the coils. You can get the the plastic plug with out removing the unit but unplugging the plastic plug this may be a little tough but, you can do it.
Make sure you pull the Power plug out of the unit or out of the wall before testing for continuity.
I hope this helps. I put a picture below. It's the only one I have. On the right of the unit under the control panel there is a metal box you can see the front if it in the picture. Most units have this box on the right side. On the left side of the box are the plugs for heat, fan and Thermal fuses.
There maybe another plug with yellow wires. the plug with the 2 black wires is the one you want. Squeeze the side of the plug to unlock the plug then just pull out and test.


Nov 09, 2008 | GE Zoneline AZ55H07D Air Conditioner

1 Answer

Dometic ac/heat pump

Would suggest it is drawing excessive current, make sure both fans are going, (inside will cycle low/high), or possible faulty reversing valve solenoid, or could be as simple as loose wire connection, how long does it run for and is it on the same 20amp breaker as the rear?if so start by running only the front unit in cooling 15/20min, check fans running, no unusual bearing noises, switch off for 60 sec then back on heat mode, if unit runs without stopping rewire onto separate circuit, if inside fan not working on heat check bi-metal switch in the airway, if running for a while, fans going but not very warm, check reversing valve.
Note, electrical's should be tested by someone who are qualified in the field.

Nov 05, 2008 | Dometic Rooftop RV Air Conditioner

1 Answer

Blower fan will not come on when set on Auto in heat mode.

the fan is controlled by a fan center or a stack switch. as burners light and heat up the spring sensor on the bulkhead above burners heats up and turns and a a point energizes the indoor fan if it gets to hot the burners go out on safty. sounds like a fan control is bad tap on them gently and they sometimes break loose but if not then have a pro replace fan control and test heat exchanger.

Oct 24, 2008 | Ruud UBHC Air Conditioner

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