Thermostat Upgrade Help

[mchur01]

Replaced my Coleman Mach today with a Honeywell RTH111B digital thermostat. Here's the issue the AC & AC fan will only run when the fan is on the "ON" position not "AUTO", but the heat works just fine. If I switch the switch on the back of the stat from "GAS" to "ELECTRIC" then the AC & AC fan work fine in auto. If I switch over to heat the heat comes on & works fine but the AC fan comes on also. If I turn the AC breaker off & start the heat then the AC fan won't come on, help please! Or should I just leave the AC breaker off when running the heat & call it good.

[mfMcFroggierPod]

Have you gone into the advanced setup?

[mfMcFroggierPod]

Manual Page 8&9

[mchur01]

It's not a programmable one.

[mfMcFroggierPod]

I know this is NOT a programmable one. The advanced setup selects the proper heat type. This could affect having the wrong settings. Read pages 8 & 9 of manual.

[mchur01]

Ok, I see it now. Any idea on what selection it may be? Or just go with the trial & error technique.

[mfMcFroggierPod]

I would trial and error
My guess would be #2
Because you don't need a 2nd blower running.
When it calls for heat it should send a signal to activate the heat w/o a blower signal. Just my Guess.
Good Luck /Advise?

[rockfordroo]

Check your wiring. Here's mine.

If you didn't add the fan speed switch, you need to pick a speed and connect that wire (green or gray) to the G connection and tape off the other one.

The gas/elec switch should be in the gas position.

[mchur01]

Ok, so I'm totally baffled. Wiring is correct I triple checked that before I even turned power back on, I just went with the green wire for fan high since that's what we always have it set on anyway. So today I entered the advanced setup as suggested, went from 5-5 to 5-4 (4 isn't even listed in the manual) & everything worked as it should. I continued on to 5-3 & 5-2 and everything worked properly. I then decided to go back to the default of 5-5 and the darn thing worked properly. Checked all the wire connections & made sure (gray) fan low & (blue) 12v- were still taped & not touching anything. All wiring checked out again. So long story short everything is working in default settings now. Thank you all for your suggestions.

[rockfordroo]

Sometimes they just want a little TLC!

[suprheat]

I replaced my 2109s original cheapie analog Coleman tstat with a Coleman digital (http://www.rvupgradestore.com/v/vspf...thermostat.pdf - direct replacement that has 2 position fan switch too). I don't have a wiring schematic on how the A/C and heating are wired but I know that my furnace will operate on 12vdc. The wiring diagram that came with the stat is the same as the left side of your diagram, so it shows DC pos and neg going to tstat. In my 40 years experience as a HVAC tech, I've never seen a tstat that needed both potentials from power to operate an analog tstat. Only a few digital actually need both potentials too so I'm confused that your diagram says the minus side is not needed. I can't find anything about your RT111 that says it will work with 12vDC. Household control systems operate on 24vAC. I'm not sure where you got that wiring diagram but I don't think that tstat will work. (if you can find a Rockwood HVAC wiring schematic that shows how the low voltage is connected, I'd certainly appreciate it!)

[rockfordroo]

Originally Posted by suprheat

I replaced my 2109s original cheapie analog Coleman tstat with a Coleman digital (http://www.rvupgradestore.com/v/vspf...thermostat.pdf - direct replacement that has 2 position fan switch too). I don't have a wiring schematic on how the A/C and heating are wired but I know that my furnace will operate on 12vdc. The wiring diagram that came with the stat is the same as the left side of your diagram, so it shows DC pos and neg going to tstat. In my 40 years experience as a HVAC tech, I've never seen a tstat that needed both potentials from power to operate an analog tstat. Only a few digital actually need both potentials too so I'm confused that your diagram says the minus side is not needed. I can't find anything about your RT111 that says it will work with 12vDC. Household control systems operate on 24vAC. I'm not sure where you got that wiring diagram but I don't think that tstat will work. (if you can find a Rockwood HVAC wiring schematic that shows how the low voltage is connected, I'd certainly appreciate it!)

I made the drawing and I can assure you that it works fine. The new tstat is battery operated, so it doesn't need a ground OR a positive and therefore also doesn't care about 12VDC or 24VDC. With respect to the analog Coleman Mach, I'm guessing they wire them all as if they were digital with brains that need power; if an analog one is used, they just don't have a ground internally; the bimetallic switch will still connect the positive power to either the furnace or the AC.

[rockfordroo]

Originally Posted by rockfordroo

I made the drawing and I can assure you that it works fine. The new tstat is battery operated, so it doesn't need a ground OR a positive and therefore also doesn't care about 12VDC or 24VDC. With respect to the analog Coleman Mach, I'm guessing they wire them all as if they were digital with brains that need power; if an analog one is used, they just don't have a ground internally; the bimetallic switch will still connect the positive power to either the furnace or the AC.

Here's an updated drawing that may help.

[suprheat]

That's great! Still I don't see a reason to fuss around with that tstat and lose high/low fan functionality just to save a few bucks. Some posts show adding a little toggle switch to perform the high/low function but still, just get the right one and be done with it, is what I say.

[rockfordroo]

Originally Posted by suprheat

That's great! Still I don't see a reason to fuss around with that tstat and lose high/low fan functionality just to save a few bucks. Some posts show adding a little toggle switch to perform the high/low function but still, just get the right one and be done with it, is what I say.

Until recently, you couldn't get a plug-and-play digital that would replace what you already had. For example, my 2012 Roo 19 had the old crappy Suburban analog:



Also until recently, the plug-and-play digitals were quite a bit more $$ than a home digital and a small switch. Doing an internet search just now for a digital Coleman Mach, the cheapest I found is around $50. That's twice the $25 I paid for the RTH111 and a small switch.

If you have the crappy Suburban, you don't have 2 speeds either, so all you need is the digital T-stat.

It's like a lot of what we do here: if you have a little know-how and enjoy doing mods, you can save $25. If you don't, you go with the plug-and-play.

[suprheat]

Well I was more referring to having an ugly 2-speed switch sticking out the side of the t-stat and along with the trip to radio shack, the cost factor changes greatly. Single speed fan, I'd probably go the route you went however I'm not sure how you knew it would work on 12vDC since they're made for 24vAC.

[Bama Rambler]

Originally Posted by suprheat

... I'm not sure how you knew it would work on 12vDC since they're made for 24vAC.

If you look at that thermostat's manual you'll see that it's for millivolt systems also. And being that the controls are just a set of relays, it doesn't really care what the control voltage is. But being a HVAC tech for 40 years, I'm sure you already know that.

[rockfordroo]

Originally Posted by suprheat

Well I was more referring to having an ugly 2-speed switch sticking out the side of the t-stat and along with the trip to radio shack, the cost factor changes greatly. Single speed fan, I'd probably go the route you went however I'm not sure how you knew it would work on 12vDC since they're made for 24vAC.

As I show on the wiring diagram, you can use a standard RV type switch mounted next to the T-stat. I'm seriously considering the JR Products 12625:



If you're really an RV tech, you probably have easier access to this switch than the rest of us. Wire it so UP is high speed and DOWN is low speed. Comes in your choice of colors.

And don't confuse what's needed to power the "brains" vs what's sent through the relay contacts. Don't necessarily need to be "the same." The Honeywell uses 3VDC (the battery) to power the brains that send 12VDC through the relay contacts. Another example: Suburban "L" model water heaters use 12VDC to close a relay that supplies 110VAC to the heating element.

But you're correct in that if I'd tried to use a home T-stat that wasn't battery powered, I MIGHT have had an issue trying to power it with 12VDC. But since logic circuits are DC, even a 24VAC T-stat would have a rectifier circuit to convert it to DC to power the "brains." But you can put DC on a rectifier and it will work. Only question is if 24 volts vs 12 volts would still be OK.

[dnmatt7]

Originally Posted by rockfordroo

Check your wiring. Here's mine.

If you didn't add the fan speed switch, you need to pick a speed and connect that wire (green or gray) to the G connection and tape off the other one.

The gas/elec switch should be in the gas position.

This worked perfectly for me. The drawing was a life savior. Thanks!

[rockfordroo]

Originally Posted by rockfordroo

Check your wiring. Here's mine.

If you didn't add the fan speed switch, you need to pick a speed and connect that wire (green or gray) to the G connection and tape off the other one.

The gas/elec switch should be in the gas position.

Originally Posted by dnmatt7

This worked perfectly for me. The drawing was a life savior. Thanks!

You're welcome!