Dometic Thermostat Problem Operating Suburban Furnace

[peteco]

Having trouble with my Suburban gas furnace not coming on at times. I think the Dometic thermostat is getting flaky, as I can fiddle with it and the furnace will sometimes come on, but then not come on at the next need for heat. The Dometic thermostat controls the furnace and the CoolCat heatpump. I have never been very happy with the Dometic controlling the temperature consistently anyway. So I am thinking about installing a heat only thermostat for just the furnace. Suburban makes the 161154 thermostat, which is analog and simple. Has anyone used this for the furnace, or gone with a digital heat only thermostat? A digital thermostat needs batteries, which is somewhat of a hassle to deal with. Is it worth the little bit of hassle if the digital offers significantly better performance?

[peteco]

Here is the Suburban thermostat I am considering.

https://www.amazon.com/dp/B003G9DD8S...v_ov_lig_dp_it

[avanti]

Many of those old-school mechanical thermostats make a surprisingly obnoxious "clunk" sound when they kick on or off. We couldn't stand the one that came with our old Airstream Interstate and ended up replacing it with an electronic one from Home Depot. Worked great. The battery was just a standard AAA (maybe two), and lasted forever.

[peteco]

Originally Posted by avanti

Many of those old-school mechanical thermostats make a surprisingly obnoxious "clunk" sound when they kick on or off. We couldn't stand the one that came with our old Airstream Interstate and ended up replacing it with an electronic one from Home Depot. Worked great. The battery was just a standard AAA (maybe two), and lasted forever.

Interesting, as my very limited experience is the opposite. Had my house Ruud mechanical thermostats (no clunk noise) replaced with a fancy Honeywell. The Honeywell had such a loud clunk I put the Ruud back in for my first floor unit. The Honeywell for the upstairs clunks also, but I left it and the kids just had to deal with it. I assumed the clunk is from a relay.

The Dometic is quiet. The Suburban does not look like it has a relay so I hope it would be quiet. I will check out what Home Depot has in electronic thermostats.

[avanti]

Originally Posted by peteco

Interesting, as my very limited experience is the opposite. Had my house Ruud mechanical thermostats (no clunk noise) replaced with a fancy Honeywell. The Honeywell had such a loud clunk I put the Ruud back in for my first floor unit. The Honeywell for the upstairs clunks also, but I left it and the kids just had to deal with it. I assumed the clunk is from a relay.

The Dometic is quiet. The Suburban does not look like it has a relay so I hope it would be quiet. I will check out what Home Depot has in electronic thermostats.

This is the one we replaced:



It literally woke us up at night.

I can't remember exactly what we replaced it with, but it was roughly like this:



https://www.homedepot.com/p/Honeywel...111B/203539510

It was silent.

[peteco]

Originally Posted by avanti

This is the one we replaced:



It literally woke us up at night.

I can't remember exactly what we replaced it with, but it was roughly like this:

That thermostat looks somewhat similar to the Suburban one. I wonder what causes the click???

[mkguitar]

older thermostats have a bubble of mercury within a glass bulb on a bi-metallic coil.


newer use relays ( click) or electronic controls.


on the old thermostat there is nothing to go wrong unless the bimetallic coil suffers physical damage.

[avanti]

Originally Posted by mkguitar

older thermostats have a bubble of mercury within a glass bulb on a bi-metallic coil.

I think the latest (last?) generation of inexpensive non-electronic stats eliminated the mercury bulb in favor of a simple dry-contact bi-metallic strip that switched on and off with a mechanical "snap". Depending on the design, it can be very loud when it switches.

[peteco]

Originally Posted by avanti

I think the latest (last?) generation of inexpensive non-electronic stats eliminated the mercury bulb in favor of a simple dry-contact bi-metallic strip that switched on and off with a mechanical "snap". Depending on the design, it can be very loud when it switches.

That makes sense.

Looking at reviews for mechanical thermostats it looks like there can be a problem when using the thermostat in very cold temperatures at the beginning inside the van. Some report having to hold the temperature lever until it warms up enough for the temperature sensitive spring to hold it in place. That would be a major hassle, as the van inside temps can be in the 40s, or even less when returning from a day out.

[TX-Trek]

I realize you've got the original ac, but at the end of this thread I described installation of a simple mechanical thermostat for the furnace. Zero issues with it, its worked well in all situations.However, note that my installation was related to a new non-heat pump ac. The entire system has worked perfectly in very hot and very cold temps.

https://www.classbforum.com/forums/f...out-11478.html

[peteco]

Originally Posted by TX-Trek

I realize you've got the original ac, but at the end of this thread I described installation of a simple mechanical thermostat for the furnace. Zero issues with it, its worked well in all situations.However, note that my installation was related to a new non-heat pump ac. The entire system has worked perfectly in very hot and very cold temps.

https://www.classbforum.com/forums/f...out-11478.html

Thanks. That helps a lot. Since the CoolCat still works, I may just run a new control line from the furnace to the new thermostat. I will place the new thermostat in the panel area above the furnace.

Is the new thermostat quiet (does it make clicking noise)?

[TX-Trek]

It clicks but its not loud, I had to think about it to answer lol. Never has woken us up, the furnace itself is way louder than this small thermostat could ever be.

[jakegw2]

check out this thread: https://www.classbforum.com/forums/f...tat-12204.html

[peteco]

Originally Posted by jakegw2

check out this thread: https://www.classbforum.com/forums/f...tat-12204.html

Thanks. Interesting older discussion. I like booster's comments that indicate that some of the older stuff is better. I am finding that true on many items these days. Sad commentary on the state of design and manufacturing, which is adversely influenced by management goals of reduced cost in order to maximize profit.

[booster]

Originally Posted by peteco

Thanks. Interesting older discussion. I like booster's comments that indicate that some of the older stuff is better. I am finding that true on many items these days. Sad commentary on the state of design and manufacturing, which is adversely influenced by management goals of reduced cost in order to maximize profit.

Interesting that the old discussion came up, as it was before I found out a few different things regarding the digital thermostats by testing the ones we had tried.

Many, including Honeywell shut off the heat at least 2* before the room temp is reached to try to prevent overshoot. Personally, when it is recovering from and night setback I want it to stay fired until the house is at full temp, but they don't see it that way. One highest end Emerson touch panel digital does let you set full high heat in recovery to set temp, but they may still stop early to prevent overshoot. It isn't clear how that works and we haven't tested one. They are high end but don't have learned recovery timing, so they were out right off the bat for us.

Another, totally unexpected thing I found in my testing is that the digital thermostats, at least the one from Emerson and Honeywell I tested, fudged the temp display to make you think you are at setpoint when you are under it be an amount. The Emerson would routinely display 4-5*F higher than actual room temp on a recovery cycle and "by coincidence" what it displayed was also the setpoint. On normal temps with natural temp swings it tracked other thermometers so it was obvious manipulation. The Honeywell did the same, but it was 2*F every time and coincided with the shutoff point to prevent overshoot and the switch from high fire mode to low fire. It still was 2* over what the other thermometers read however so the same manipulation.

This sort of crap is almost impossible to do in a mechanical thermostat because the thermometer reading and control are separated and can't be manipulated to fool the customer.

Needless to say, I was very, very disappointed to find stuff like this going on as I think it is truly dishonest.

Digital could be great if they gave you the settings that are really needed and didn't fudge the data to make you think they are working better than they are.

[avanti]

In our forthcoming rig, I anticipate eventually taking over direct control of the Espar, the A/C, the MaxxFan, and their respective fan speeds via Home Assistant, and thus acquiring complete control of the behavior of the system, based on both indoor and outdoor temperatures. HA is quite sophisticated at this kind of thing, so it shouldn't be rocket science. There will be a number of higher-priority projects post-delivery, though, so it is probably going to take awhile.

I realize that this kind of thing isn't for everybody, but I expect to dramatically improve the comfort and convenience of the rig over time. Even if you didn't want to get that elaborate, using ESPhome to build a stand-alone thermostat from scratch would be a pretty easy beginner's project for anyone with any kind of programming background.

[peteco]

Originally Posted by booster

Interesting that the old discussion came up, as it was before I found out a few different things regarding the digital thermostats by testing the ones we had tried.


Many, including Honeywell shut off the heat at least 2* before the room temp is reached to try to prevent overshoot. Personally, when it is recovering from and night setback I want it to stay fired until the house is at full temp, but they don't see it that way. One highest end Emerson touch panel digital does let you set full high heat in recovery to set temp, but they may still stop early to prevent overshoot. It isn't clear how that works and we haven't tested one. They are high end but don't have learned recovery timing, so they were out right off the bat for us.


Another, totally unexpected thing I found in my testing is that the digital thermostats, at leas the one from Emerson and Honeywell I tested, fudged the temp display to make you think you are at setpoint when you are under it be an amount. The Emerson would routinely display 4-5*F higher than actual room temp on a recovery cycle and "by coincidence" what it displayed was also the setpoint. On normal temps with natural temp swings it tracked other thermometers so it was obvious manipulation. The Honeywell did the same, but it was 2*F every time and coincided with the shutoff point to prevent overshoot and the switch from high fire mode to low fire. It still was 2* over what the other thermometers read however so the same manipulation.



This sort of crap is almost impossible to do in a mechanical thermostat because the thermometer reading and control are separated and can't be manipulated to fool the customer.


Needless to say, I was very, very disappointed to find stuff like this going on as I think it is truly dishonest.


Digital could be great if they gave you the settings that are really needed and didn't fudge the data to make you think they are working better than they are.

That explains some wonky numbers I observed on our house Honeywell thermostat. I agree, I don't like them assuming what people want. It is fine if they have a nominal setting that they think most people would want. But give the option for custom settings and describe why one might want to do something different than the baseline setting.

Here is an interesting discussion on how the heat anticipator works on a mechanical thermostat. Pretty clever. Sounds like this function is programmed into digital thermostats in various manners. Again, give the owner an option to adjust.

https://inspectapedia.com/heat/Heat-...-Operation.php

[booster]

Originally Posted by peteco

That explains some wonky numbers I observed on our house Honeywell thermostat. I agree, I don't like them assuming what people want. It is fine if they have a nominal setting that they think most people would want. But give the option for custom settings and describe why one might want to do something different than the baseline setting.

Here is an interesting discussion on how the heat anticipator works on a mechanical thermostat. Pretty clever. Sounds like this function is programmed into digital thermostats in various manners. Again, give the owner an option to adjust.

https://inspectapedia.com/heat/Heat-...-Operation.php

Yep, the anticipators have traditionally been just a little electric heater and the adjustment is a rheostat to supply the heater various amounts of energy. Easy to understand and easy to use, to adjust the system to building it is in for best results.

[hbn7hj]

Just a little FYI. The hysteresis of the analog Dometic Coolcat thermostat is nearly 10F.

You could use a battery powered digital thermostat to get a +/- 1F hysteresis. The furnace control wires are the green wires.

The other way to do it is to replace the Coolcat with a new one with a digital thermostat, which is what I did. If you do that install an Easystart or Softstart for another $300. Total bill is $1500 plus a big PIA. Works great!

[tarp]

Originally Posted by hbn7hj

Just a little FYI. The hysteresis of the analog Dometic Coolcat thermostat is nearly 10F.

You could use a battery powered digital thermostat to get a +/- 1F hysteresis. The furnace control wires are the green wires.

The other way to do it is to replace the Coolcat with a new one with a digital thermostat, which is what I did. If you do that install an Easystart or Softstart for another $300. Total bill is $1500 plus a big PIA. Works great!

Is the new coolcat any quieter all in all?