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Old 12-01-2006, 04:36 PM   #1
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Is there a homestyle replacement thermostat for the True Air Coleman Mach thermostat? I would like to be able to program temps and times.

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Old 12-01-2006, 04:36 PM   #2
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Is there a homestyle replacement thermostat for the True Air Coleman Mach thermostat? I would like to be able to program temps and times.

Thanks
Jim
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Old 12-02-2006, 04:41 AM   #3
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Jim - I seriously doubt it. The thermostat does some "magic" about starting one or two compressors due to the limited power we have to work with in the coach. But this is only a guess so maybe you will get a more qualified opinion from somebody else.
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Old 12-02-2006, 05:12 AM   #4
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John, plus the fact that it has 2 heat modes. I have not seen any like that in the stores.

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Old 12-02-2006, 06:39 PM   #5
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Jim and John
All thermostats that I have access to both residential and commercial are 24 volt AC.There are many commercial thermostats that come with up to three stages of heating and cooling.But here is the issue our thermostats are 12 volts DC.
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Old 12-04-2006, 05:43 AM   #6
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I've done a bit of research on this as I plan to replace mine because I don't particularly like the programming on the Coleman, and I also want to cool off the motor home at night. I believe it woud be possible to use a high end dual stage AC/dual stage Heat programmable heat pump thermostat. It would have to be heat pump compatible, and have dual stage heating and cooling. The one thing that I want that I cannot find in a replacement programmable thermostat is the ability to set when the 2nd stage heat comes on independant of the 1st stage.
If you have not already done so, you would need to get the wiring diagrams for the thermostat, heat pumps and LP furnace from Winnebago's web site. It will require special wiring, and doing this incorrectly could damage your equipment.
1. While true that residental control circuits are 24VAC, usually the programmable thermostats actually run on AA batteries and use relays to cycle heat/ac/fan modes. While this should be verified by tracing the circuits on the thermostat, it makes since that nothing in the thermostat really uses the 24VAC because all the electronics would require low voltage DC.
2. As for power management, this is done by the powerline system and the thermostat never really knows whether one or two compressors are running. The thermostat just sends 12V to the relays in the heat pump (and LP furnace) and if the powerline is sending AC to that circuit, it comes on.
3. In heating mode, you would connect the 1st stage of the thermostat to the heat pump. In heating mode, Coleman tries to run both compressors (depending on power availablity) all the time. The 2nd stage could be connected to the LP furnace. Note however this seriously changes the nature of how the 2 heat sources work. The orig thermostat runs the heat pump until the temp drops 5 degrees below set point and then turns on LP. It repeats this cycle 3 times, then locks out the HP for a few hours (doc says 2, but it seems longer on mine). With most programmable thermostats, 1st stage comes on at either .5 or 1 degrees below setpoint, and 2nd stage cycles at 2 degrees below setpoint.
4. In cooling mode, you would connect 1st stage cool to compressor 1 circuit, and 2nd stage to compressor 2 circuit. This would work identical to the orig Coleman thermostat.
Please note that this is all theory at this point as I have not attempted to do this yet.
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Old 12-04-2006, 07:50 AM   #7
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Some great info here.

And while on the subject. We needed to replace our thermostat. There are two different ones in the Winnebago catalog (besides black and white). They appear the same except for a choke coil. Are they? When would the choke coil be required?
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Old 12-04-2006, 08:16 AM   #8
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swyates: Consider this link 3 heat/2 cool Thermostat

tderonne, here's good info about using a Hunter Thermostat (from Home Depot or Lowes):
Hunter T'stat
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Old 12-04-2006, 03:51 PM   #9
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Thanks troth, I will follow up on those threads.

Jim
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Old 12-04-2006, 06:21 PM   #10
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swyates
jimandsue

You made me think
Look at a Honeywell TH8000 VisionPro
#TH8321U1008 Touch Screen Thermostat
Either 24 volt ac or battery operated
3 stages of heat
2 stages of cool
Programmable
Conventional and or heat pump
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Old 12-05-2006, 03:37 AM   #11
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Ed,

Thanks for the idea on the Honeywell Thermostat. I have been thinking of doing something like this too.
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Old 12-05-2006, 10:57 PM   #12
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Well I did manage to replace the stock Coleman-Mach thermostat with a $79 full-featured digital touch screen unit from Home Depot. The slide switch on the Coleman was getting more & more flaky, and my warranty was gone. To avoid spending $150-300 for another featureless stock Coleman, I was highly motivated to figure how to adapt a digital setback model. This job took me many, many hours to figure out the wiring. I had to measure voltage swings on all the wires, in all the different conditions, break down and understand the schematics of the heat pump unit, the Coleman stat, an the RiteTemp schematics. I sure didn't want to blow out the control circuits or bypass the delay function that protects the compressors.

I found that a RiteTemp Model 8085C for a dual stage heat pump with control for auxiliary heat strips fit the bill. It is battery operated and has floating contact closures to control the heat pump unit and kick in the gas furnace if the heat pump can't keep up or if you set the temp more than 4 deg warmer than ambient. It doesn't have the 2 speed fan switch so you wire it for hi speed only, but the Winnie Energy Management System will still cut the speed to low to save power on 20 or 30 amp service.

It has some really great features:
---It records the number of hours of actual furnace run time and will notify you to clean/replace the filters when it hits the hrs you preset.
---You set the swing temp for up or down to get the cycling time that suits you & your coach conditions.
---You can off-set the temp reading to be calibrated to a more accurate temp somewhere else (like next to your favorite chair).
---Backlite touch screen with very large numbers and very intuitive to use.
---Measures humidity and can set a limit to control a humidifier if you really need one.
---It comes programmed with an "Energy-Star" program which works great for us. But if you want, it has 4 program periods/day on Program A, and 2 or 6 periods/day on program B.
---If the coach is too hot/cold, just tap the display up/down a few degrees to override program.

I have a hand sketch of the wiring that is working in my '04 Winnie coach, but I would have to clean it up so it could be used to show exactly what wire goes where. I'm thinking a drawing that shows existing Coleman stat terminal connections crossed over to new RiteTemp terminals is all that is needed. I believe all the Winnie's with basement AC/Heat pump use the same Coleman thermostat for many years. It'll take me a few days to pull all the info together to publish here. Also I don't know how to upload a pdf to the forum when I have a schematic ready. If someone could PM the info to me that would be helpful.

This link will take you to the RiteTemp website where you can download the Installation Guide and Operation Guide:
8085C

Here's the 29 page application guide:
Download Professional Application Guide

Happy Trails,
Bill
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Old 12-06-2006, 01:34 AM   #13
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I believe that the True air is actually a 3 stage unit. You have two compressors and a furnace. Only one compressor runs if the temperature is close to set point and if it is over two degrees from set point, both compressors come on. Then you also have the furnace to deal with.
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Old 12-06-2006, 02:02 AM   #14
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Wow, nice job Duner! I look forward to seeing the wiring schematic and how it hooks up to your coach.
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Old 12-06-2006, 03:39 AM   #15
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Duner, Thanks for the info. How do you switch that thermostat between heat pump and gas heat? Looking at the info on the pages you provided I only the the 1 heat/cool switch.

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Jim
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Old 12-06-2006, 04:34 PM   #16
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jimandsue60:
Duner, Thanks for the info. How do you switch that thermostat between heat pump and gas heat? Looking at the info on the pages you provided I only the the 1 heat/cool switch.

Thanks
Jim </div></BLOCKQUOTE>
Yes, Jim there's no gas/elect heat switch position. But there's two ways to go on this point.
Option ONE:
Using the RiteTemp, if you're dry camping with no 110v, then you can switch to heat position and only the gas heater will come on. The RiteTemp has a function called EMER[ency] heat and if you press this on, it will force the gas heater on (just went out to my mh and tried this function). It may regulate at the set temp, I don't know since I didn't leave it on long enough. If 110v is present heat pump will always come first. Most of the time folks want to conserve the propane fuel so using 110v is 1st choice anyway.
Option TWO:
For a couple years now I have been using a little cheap ($20) digital set back thermometer for gas heater only. I installed it just around the corner from the original Coleman and used them both. Controlling the gas heater is real simple, just contact closure from +12V to the control wire. This can be added in parallel without disturbing any of the existing Coleman wires. This worked great when dry camping, where I set back the temp real low (50deg or lower) while sleeping to save the batteries by not cycling heat all night long, then 30 min before I get up the it kicks on and gets real toasty when I have to throw off the blankets & get up. So at this point I have two digital thermostats and use them both. In a campground with 110v I use only the RiteTemp for AC or heat pump. In my earlier post I didn't want to confuse everybody so I didn't mention the 2nd setback. thermometer.
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Old 12-06-2006, 06:45 PM   #17
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Charles99:
I believe that the True air is actually a 3 stage unit. You have two compressors and a furnace. Only one compressor runs if the temperature is close to set point and if it is over two degrees from set point, both compressors come on. Then you also have the furnace to deal with. </div></BLOCKQUOTE>
Charles, you're right, the 3rd stage is gas heat. The RiteTemp is only 2 stage where the 2nd stage can be a 2nd compressor or be the auxiliary electric heat strips. I wired 2nd stage for gas furnance which more closely matches the Coleman. RiteTemp can be set for 2, 3, or 4 deg spread before the gas heat is called to come on. I set the RiteTemp for 4 deg since that is close to the Coleman which is designed for 5 degrees.

Troth -- Thanks for the complement

Happy Trails,
Bill
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Old 12-06-2006, 07:57 PM   #18
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I've thought about replacing the RVP True Air thermostat since day one. After reading this thread I reviewed the RVP 6535*335 (Winnebago)Thermostat Reference Guide and learned some things relevant to this discussion:
<UL TYPE=SQUARE><LI>Electric heat mode is only two stages as far as the thermostat is concerned. Stage 1 call energizes both compressors (there's a built in 30 second delay to energize the second compressor). Stage two call is the gas furnace if the temperature difference is more 4 degrees or more.<LI>The heat pump will be locked out of operation for two hours (DIFF on LCD display) if there are three calls in a row for stage two heat (furnace) after the heat pump fails to satisfy the thermostat setting (aka 3 strikes). During the lockout period only the furnace will work. After the two hour lockout then each time the heat pump fails satisfy the thermostat it will be locked out again. This is obviously a safety mechanism to not stress the heat pump if it's has a legit problem or if the outside temperature has reduced it's efficiency to low that it can't provide heat (about 27F from what I know about heat pumps).<LI>Evaporator freeze control is controlled by the thermostat and not by any logic in the heat pump itself (this is way different than a home heat pump which has most of its smarts in the heat pump unit).<LI>and more....[/list]Given the specialized programming this unit has it appears to me it is not just a thermostat but rather a very integral part of the heat pump system. Replacing it with an aftermarket unit strikes me as risky.
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Old 02-03-2007, 10:02 PM   #19
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Jon brought up some issues that sent me back digging thru the schematics and assessing the results I've been getting in my coach for the past two winters using the RiteTemp stat. Since last year I'm been camping in 112 deg high's and 23 deg lows. I want to make sure that this conversion is not sacrificing reliability for convenience.

Below are the wiring cross connections I used to install the RiteTemp and some comments about operation.

Here's what I have found:
This link to the Coleman Service Manual describes the early Coleman stat 6535-3451 which works with the same basement unit as the Coleman-Mach thermostat and does not have 3 strikes lockout feature. Looking at page 7 functional schematic, this stat has time delay circuits for sequencing and no microprocessor to count strikes and lockout. This older Coleman performs like the RiteTemp stat with two exceptions (only one fan speed, and both compressors start at the same time). The RiteTemp stat does have a 5 min delay for compressor restart protection. Regarding the compressors coming on simultaneously, I've watched the amp draw on the PowerLine display and the initial amperage is 13 amp for the blower, then 30 second delay, then 23 amp when the compressors kick in. When both compressors are running, the Winnebago EMS (energy management system) will still shut down the 2nd compressor if the power exceeds 30 amps.

Regarding freeze protection, page 32 shows schematic of the base control. Both coils have freeze switches that open the -12v to the stat when temp reaches 28+/-3 deg and will stop the compressors even using the RiteTemp stat. Both freeze switches have about 20 deg of hysteresis which should provide recovery time for the compressors. Jon stated above that "Evaporator freeze control is controlled by the thermostat and not by any logic in the heat pump itself", but that's not what I see in this diagram. I've seen the freze protection kick in on my unit in AC mode and the blower keeps on running but there is no cold air. Recovery was automatic when the ice melted and the compressors came back on.

If all of this is just too confusing and/or you feel that it is just too much of concern, there is a real simple solution to get automatic setback for your gas furnace. Leave the Coleman-Mach in place and install a 2nd digital set back thermostat just for gas furnace control. This only requires a simple contact closure across the P1-3 white wire (gas control) to P1-1 re/white wire (+12v). I've been using a second stat for 7 years in both of my Winnebagos.

Happy trails,
Bill
Here's link to higher resolution image.
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Old 04-10-2010, 10:09 AM   #20
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I could not locate the RiteTemp 8085C. The manufacturer states that the 6030 is a direct upgrade replacement. However, after carefully following all of the detailed wiring instructions from your posting, my system will not create heat from the heat pump system. I get air conditioning. I checked everything and even metered the functionality. It always looked like the system should work but we are missing some small detail. I fixed the switch on my original thermostat (this is a constant failure point on mine) and re-installed it. My heater now works (at least as well as it did originally).
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