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A. Spruce
Thermostats
A. Spruce

Hey guys, what can you tell me about thermostats? I have an old analog one that isn't functioning as it should, basically, if set on auto, the furnace fan runs at a slower speed and cycles on/off every few minutes, it's worst under high demand, like first thing in the morning when you increase the temp for daytime comfort. If you just turn the fan on, then it runs at full speed, no cycling and the house actually warms up.

Running a gas furnace with AC added to it. Current thermostat has 5 control wires, if that matters.

What I'm looking for is something that is simple and intuitive to use. A heat/cool switch, on/off switch, and a lever to control the temp is all that is needed. While it will be nigh impossible to find something that isn't an electronic atrocity, I just need the basics, I don't need ANY whistles or bells, and, I would prefer a name brand.

Any particular brand/models you can recommend?

Jack
Re: Thermostats
Jack

Spruce you need to look elsewhere for the cause. The thermostat calls for heat and the control board and other components control the blower. The control board provides power through the limit switches to turn on and off the blower. You could be having a problem with the high limit or the low limit switches.

Jack

ordjen
Re: Thermostats
ordjen

Tthat is my thought too. The thermostat is basically only an on/off switch that goes on or off with the temp set. The controls on the furnace itself controls how the unit reacts.

A. Spruce
Re: Thermostats
A. Spruce

I had a duct replaced last winter, and while the guy was here I had him check out the whole system. The cycling problem wouldn't show itself, of course, while he was here. As I recall, he checked the limit switches and said they were fine and suggested that the thermostat could be part of the problem. It was after this visit that I discovered flipping the switch to the on position, instead of auto, affected the fan speed.

Regardless of the cause, I am ok with changing out the old thermostat because I don't believe that it is accurately controlling the temps, warm or cold. If you have any experience with trailers, as this is, then you know that the general build quality to be less than sub par, most things need replacement when they're brand new, let alone 20 years in.

Fencepost
Re: Thermostats
Fencepost

If it's a 2-stage thermostat (for example, if the room temp is less than 2 degrees below the set temp, run the burner & fan on low; if it's more, run them on high), it could be a problem with the thermostat.

For an electronic thermostat, try a Honeywell RTH111B -- about $25, no programming, dead simple to operate. Available from your favorite orange store. Downside: it requires batteries.

Mastercarpentry
Re: Thermostats
Mastercarpentry

I'd go with a programmable T-stat; they're cheap enough and save you from constantly adjusting for day/night temps. I don't know anybody who hasn't liked making the upgrade. And always have an extra battery or two on hand as they only go dead at the most inconvenient times :mad:

Phil

Fencepost
Re: Thermostats
Fencepost
Mastercarpentry wrote:

And always have an extra battery or two on hand as they only go dead at the most inconvenient times

Some of them flash a low battery warning for a while before they go completely dead.

A. Spruce
Re: Thermostats
A. Spruce

Thanks for the feedback, guys, keep it coming if ya got it. :cool:

dodsworth
Re: Thermostats
dodsworth

SPRUCE,

Before you spend money on components, be aware that the first thing heating servicemen do in a situation like this is to shut off the elec power to the heating system & take a women's cardboard fingernail file & start with opening the T-stat cover & lightly file the contacts-----do this for the rest of the contacts in the ignition chain, (mostly located on or near the heating unit), including any zone valves, ignition transformers, etc., do not use a metal fingernail file!

After firing thousands of times during a heating season, the various contacts in the system get caked with a light film of crud that can seriously degrade or shut down the ignition sequence.

Mastercarpentry
Re: Thermostats
Mastercarpentry
dodsworth wrote:

SPRUCE,

Before you spend money on components, be aware that the first thing heating servicemen do in a situation like this is to shut off the elec power to the heating system & take a women's cardboard fingernail file & start with opening the T-stat cover & lightly file the contacts-----do this for the rest of the contacts in the ignition chain, (mostly located on or near the heating unit), including any zone valves, ignition transformers, etc., do not use a metal fingernail file!

After firing thousands of times during a heating season, the various contacts in the system get caked with a light film of crud that can seriously degrade or shut down the ignition sequence.

Not a good idea unless you use a very fine cut 'polishing' salon board, not an 'emery' board. Ideal is a "Points Burnisher" which mechanic's once used to dress down ignition points in cars. Good luck finding one of those these days (and I'm not selling mine). Here's the poop: Electrical contacts spark when opening or closing which burns away metal, pitting the contacts which increases resistance and makes for bigger sparks and more erosion. Ideal is a very slightly rounded well-polished contact surface so that the spark can have as much clean un-pitted area to work with as possible in close contact. Sanding or using anything coarse grooves the metal and burns the high parts quickly leaving the low spots where they can't touch making the problem return even faster. A burnisher (or a polishing board) is like 10,000 grit sandpaper giving a very, very smooth finish which helps avoid this. Us 'radio nuts' who use old rigs dress out our relays with a cardboard matchbook cover or similar since the receive current can't take any additional resistance in the circuit before things go weird. The coarser grits work faster but fail faster; a patch but not a fix.

"Sandpaper on a stick" aka "Salon Boards" is some handy stuff and you can get many grades of it in the nail care section of your local [email protected]. It works pretty good on fingernails too :p And white fingernail polish makes a decent porcelain chip repair so get some of that while you're there and hope your buddies don't happen by at the checkout line :rolleyes: :o ;) Next week we'll cover "Mini Bungee Loops" aka hair scrunchies and how to use them in home renovation projects.

Phil '

Jack
Re: Thermostats
Jack

It may be possible you have an old thermostat with a mercury switch, no contacts. When the thermostat calls for heat it just connects "R" to "W" on the furnace.

Jack

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