urbanhermit Report post Posted August 8, 2020 Circa 2006 Dometic low-profile roof unit with fancy Dometic thermostat that displays multiple modes -- Cool, Furnace, HP -- works on cool but won't turn on the LP furnace or the heat pump cycle (if there is one). Lowest I've gotten the coach interior by AC is 80 degrees. Anybody know if the thermostat requires a cooler ambient temperature to activate at least an LP furnace? (I'm not nuts -- trying to get it covered under a maintenance contract.) Share this post Link to post Share on other sites
hermanmullins Report post Posted August 8, 2020 To the best of my knowledge there is no LP to a roof top A/C with a heat pump. Herman Share this post Link to post Share on other sites
urbanhermit Report post Posted August 8, 2020 I must not have phrased my question properly. The coach has an LP furnace and a rooftop cooling unit which may be straight AC or a heat pump. I don't know which. The rooftop unit cools through a Dometic thermostat that offers "Cool," "Furn," and "HP" modes. The furnace does not come on, nor does the rooftop unit heat, in "Furn" and "HP" modes. The Coleman thermostat in the bedroom is conventional On/Off, fan Auto/Run, and temperature slide unit obviously not connected to the LP furnace. The lowest interior ambient air temperature at which I've attempted to activate the LP furnace or the possible heat pump is 80 degrees. Question is, is this too high to have the thermostat send the proper signal to either unit, or might there more likely be an equipment problem. Share this post Link to post Share on other sites
747guy Report post Posted August 8, 2020 If the original Dometic roof unit has been replaced, it may not have the HP Heat Pump option, even though the thermostat shows this option. My furnace mode is attached to my aqua hot system, so this must be turned on with a separate switch. If not,, nothing happens when furnace is selected on the Dometic Thermostat. Share this post Link to post Share on other sites
manholt Report post Posted August 8, 2020 UH, easy way to check furn in high ambient temp, is to place a frozen bag of peas, corn, carrots, etc over thermostat. Share this post Link to post Share on other sites
urbanhermit Report post Posted August 8, 2020 (edited) 1 hour ago, manholt said: UH, easy way to check furn in high ambient temp, is to place a frozen bag of peas, corn, carrots, etc over thermostat. Helpful and appreciated -- but why snark? Edited August 8, 2020 by UrbanHermit Share this post Link to post Share on other sites
urbanhermit Report post Posted August 8, 2020 1 hour ago, 747guy said: If the original Dometic roof unit has been replaced, it may not have the HP Heat Pump option, even though the thermostat shows this option. My furnace mode is attached to my aqua hot system, so this must be turned on with a separate switch. If not,, nothing happens when furnace is selected on the Dometic Thermostat. Thank you -- a possibility but I don't think so. Roof and thermostat are both Dometic and there aren't any obvious signs of replacement. Awhle back the AC got disabled by a low-hanging branch breaking an electrical connnection on the roof, or so my coach mechanic told me; maybe he didn't get all the wires reconnected, but that wouldn't explain the LP system not coming on. I think if it isn't an issue of high ambient temperature, it's likely to be a defective thermostatat Share this post Link to post Share on other sites
wildebill308 Report post Posted August 8, 2020 Try this, turn the thermostat off. Pull the front cover off. There should be a fuse, remove the fuse and test it. Removing the fuse also resets the thermostat. Put the fuse back in turn on the thermostat to heat. crank it up and see if it lights the furnace. With my last coach if you asked for more than 10 deg over ambient temp it would bypass the heat pumps and go directly to the furnace. Bill Share this post Link to post Share on other sites
urbanhermit Report post Posted August 8, 2020 19 minutes ago, WILDEBILL308 said: Try this, turn the thermostat off. Pull the front cover off. There should be a fuse, remove the fuse and test it. Removing the fuse also resets the thermostat. Put the fuse back in turn on the thermostat to heat. crank it up and see if it lights the furnace. With my last coach if you asked for more than 10 deg over ambient temp it would bypass the heat pumps and go directly to the furnace. Bill Bill -- thank you. I'll try that. Cudos for helpfulness. Share this post Link to post Share on other sites
urbanhermit Report post Posted August 8, 2020 Manholdt -- I owe you an apology. I've been thinking that your "UH" was a version of "Duh." My episodes of being thick as a brick, in my declining years, are stretching into seasons. I only just now realized you were compressing UrbanHermit. That red glow in the east isn't an early sunrise -- it's my red face. Share this post Link to post Share on other sites
urbanhermit Report post Posted August 14, 2020 On 8/8/2020 at 10:03 AM, manholt said: UH, easy way to check furn in high ambient temp, is to place a frozen bag of peas, corn, carrots, etc over thermostat. Well, it was a bag of frozen lima beans, but it worked. Got a reading below 70 and the heat pump came on. Thank you for the "hack" suggestion . The FURN mode didn't produce heat. Mother Superior may not have an LP furnace, but there are floor vents. Ya think I oughta read the owner's manual? . Only electric heat for the water, 12 or 120, and the range top lit, so LP was available. Still learning Mother Superior's quirks. Share this post Link to post Share on other sites
