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Adjust or replace Coleman-Mack thermostat for heat pump?


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#1 GeezerDropOut

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Posted 23 February 2013 - 09:14 AM

[attachment=4676:Thermostat front.jpg

The heating cycle with our 2004-vintage 2-compressor Coleman basement AC/heat pump kicks-in at an uncomfortably cool temperature, and then it does not kick-off until the temperature is uncomfortably warm. Also, the digital readout for room temperature is inaccurate: thermostat reading is 10 to 15 degrees higher than true room temperature. The symptoms are about the same for both heat pump and gas furnace. Otherwise, the thermostat is functional.

We have the Coleman-Mack Digital Wall Thermostat TrueAir Model 6535-335 (AG7839-0411). We have a 2005 Winnebago Vectra WKS40KD.

I've been told that there are no adjustments on this thermostat, and the too-cool/too-warm cycle is typical for this thermostat. I've been told to check for air drafts within interior wall where thermostat is mounted, but I'm not sure how to do that. I don't see any obvious adjustments on the thermostat. We change interior air filter regularly, and external AC/heat pump coils are clean and straight.

I can find what appears to be OEM replacement thermostat at makariosrv.com for $117. However, this is the 6535-3442 model thermostat. The makariosrv.com web site, which is very professionally done, has instructions on how to retrofit wiring on model 3443 to wiring harness for model 335. The information appears credible.

I don't mind paying purchase price if the 3442-Model will improve comfort and solve the annoying temperature readout error. Installation appears easy.

Any knowledgeable advice greatly appreciated.

Full-time RV travelers since 2011

Home base in Fort Collins, Colorado, USA

40-ft Winnebago Vectra motorhome with Jeep Wrangler toad

Please visit our website at www.GeezerDropOuts.com


#2 Jimalberta

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Posted 23 February 2013 - 11:22 AM

To check for drafts in the wall behind the thermostat you will need to remove the mounting screws holding the thermostat to the wall and let the stat hang by its wires for a little bit..then feel for cool air coming out the hole that you will see the wires coming out of. Sometimes it helps to hold a feather or lit match or something that is very sensitive to air movement. If you do find a draft it will definitely affect the performance of the thermostat.

To rectify this , seal the hole with some putty or caulking and I would also use a spacer to have the thermostat mounted away from the wall about 1/2 inch to allow some air circulation behind the thermostat...this helps the thermostat to function a lot more accurately.

....JIM and LINDA..He..retired Refrigeration , Heating and A/C tech for 44 years and counting. she ...retired bookkeeper.....2001 American Eagle 40 '.towing a GMC Sierra 1500 4X4 with RZR in the rear. 1999 JEEP Cherokee that we tow as well.
IT IS A CONTENTED MAN WHO CAN APPRECIATE THE SCENERY ALONG A DETOUR.


#3 GeezerDropOut

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Posted 23 February 2013 - 11:32 AM

To check for drafts in the wall behind the thermostat you will need to remove the mounting screws holding the thermostat to the wall and let the stat hang by its wires for a little bit..then feel for cool air coming out the hole that you will see the wires coming out of. Sometimes it helps to hold a feather or lit match or something that is very sensitive to air movement. If you do find a draft it will definitely affect the performance of the thermostat.

To rectify this , seal the hole with some putty or caulking and I would also use a spacer to have the thermostat mounted away from the wall about 1/2 inch to allow some air circulation behind the thermostat...this helps the thermostat to function a lot more accurately.


Fine recommendations. I'll post outcomes in the future.

Full-time RV travelers since 2011

Home base in Fort Collins, Colorado, USA

40-ft Winnebago Vectra motorhome with Jeep Wrangler toad

Please visit our website at www.GeezerDropOuts.com


#4 Kirk

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Posted 24 February 2013 - 08:17 AM

On the substitute thermostat, I have no experience with your issue but I do know that I have had excellent service from Mark's RV in the past with what I purchased there. I would tend to believe what they say if they claim you can make that change. You may want to contact them to see if there is any adjustment for the range of the thermostat's on/off cycle as many thermostats do have an adjustment for that.

On the draft issue, I once saw an RV which had such a problem and the owner solved it by making up a box as an air diffuser which he mounted to the wall with the thermostat inside of it. His box was made of plexiglass and was large enough to allow about 2" of space on all sides of the thermostat and the sides extended out about 2" into the room beyond the face of the thermostat. I saw it and asked and he said that before that for some reason the natural air currents in the RV would cause temperature inaccuracy on his thermostat, but that by blocking the currents, the problem was solved. This was only a one time visit into the RV where this happened and we only spent a few days as neighbors so I really don't know much about the owner or the problem, but the box seemed to make sense. ;)

Good travelin !...............Kirk

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#5 Newt

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Posted 24 February 2013 - 08:34 AM

On the draft issue, we do just the opposite. Our ceiling fan is in the vicinity of the thermostat. We leave it on most of the time to hot or cold s;pots and keep the temperature more constant.

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#6 Jimalberta

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Posted 24 February 2013 - 01:04 PM

On the draft issue, we do just the opposite. Our ceiling fan is in the vicinity of the thermostat. We leave it on most of the time to hot or cold s;pots and keep the temperature more constant.

Newt


I agree with you Newt...by doing it this way you are evening out the air temp in your living space and getting a much more accurate control of temps.

....JIM and LINDA..He..retired Refrigeration , Heating and A/C tech for 44 years and counting. she ...retired bookkeeper.....2001 American Eagle 40 '.towing a GMC Sierra 1500 4X4 with RZR in the rear. 1999 JEEP Cherokee that we tow as well.
IT IS A CONTENTED MAN WHO CAN APPRECIATE THE SCENERY ALONG A DETOUR.


#7 GeezerDropOut

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Posted 16 March 2013 - 10:17 AM

Final chapter (hopefully): 
 
I never did find evidence of draft between walls, but I did fabricate a simple spacer that plugged most of the 2-inch diameter hole in the wall behind the thermostat. I figured that was the easiest potential fix. The spacer is about 1/2-inch thick, so the thermostat has a little better exposure to ambient air. 
 
After a few weeks, we decided that the thermostat still didn't perform as it should.The thermometer would register 99-degrees when it was no where near that temperature. The cooling cycle was off calibration too.
 
I did purchase an OEM replacement at http://www.makariosr...-air-6535-3442/ and was very happy with customer service. I followed simple directions that adapted the new 6535-3442 model to the old  Model 6535-335 wiring harness. I just finished closing up, and the air conditioner seems to be running satisfactorily. I'll add a post latter if any issues remain. 
 
Otherwise, mission accomplished. Thank you to all who responded to my query and helped my out!

Full-time RV travelers since 2011

Home base in Fort Collins, Colorado, USA

40-ft Winnebago Vectra motorhome with Jeep Wrangler toad

Please visit our website at www.GeezerDropOuts.com


#8 Jimalberta

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Posted 16 March 2013 - 10:34 AM

Thanks for the post...its always nice to hear of results..positive or negative.


....JIM and LINDA..He..retired Refrigeration , Heating and A/C tech for 44 years and counting. she ...retired bookkeeper.....2001 American Eagle 40 '.towing a GMC Sierra 1500 4X4 with RZR in the rear. 1999 JEEP Cherokee that we tow as well.
IT IS A CONTENTED MAN WHO CAN APPRECIATE THE SCENERY ALONG A DETOUR.