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Is my Honeywell T87F HVAC thermostat getting old?

NickD on Wed November 04, 2009 6:41 AM User is offline

Was working perfectly with my old furnace, but had to increase the heat anticipator from 0.3 to 0.7 with the new furnace. Least that is what the instructions state.

Here is the problem, when I set it to 70*F, it heats the house to 70*F, but when I set it to 72*F, it heats the house to 74*F, I prefer 72*F, 74*F is too warm and the air feels a lot dryer.

When I rotate the thermostat setting to 74*F, two things happen, that long outlawed mercury switch bulb goes slightly off the peak to the right, maybe that bimetallic coil is getting tired keeping it in the heat cycle longer, that bulb is comparatively heavy. The other thing that could be wrong, it has three very fine vinyl insulated wires in a form C configuration, maybe the vinyl is getting stiff binding the return of that mercury filled bulb. It's only 30 years old, those are possibilities. I did check the heat anticipator, nice and continuous between 0 to 6.7 ohms, is in series with the gas valve, suppose to heat up right next to that bimetallic coil to reduced the hysteresis of that relatively heavy mercury filled bulb. Set at 4.67 ohms at 0.8. It was made in the USA, getting hard to fine stuff today made in the USA.

Did look at new Honeywell's, claim no more dangerous mercury, oh my God, I have mercury in my home, am I going to die? Have no idea what's inside the new ones. But suppose I could lay out 40 bucks and find out if it's any good or not, package says it's made in China, is that a good sign?

Did buy one of those digital programmable thermostats a few years back, really don't know if they are making those better today. The package still says I can save thousands of dollars on my heating bill. Only thing I really noticed is the chairs on my dinning room set were falling apart due to constant thermal cycling and mold was building up in the closed space closets, not a damn bit of difference on my heating bill. But if I do buy a new one, can get a tax credit on it. The final straw to removing it, the damn thing crashed and I got no heat at all. Could be reset, but more of that crazy digital stuff that is also driving me nuts in my cars, so I went back to my good old made in the USA Honeywell.

Terrible getting old with the habit of buying good stuff in this country, when I shop today, only see junk, in my neck of the woods, leaving my home for a couple of days can be a disaster if the heat doesn't come up, all the plumbing would freeze up causing thousands of dollars worth of damage. So, I am looking for a new thermostat, but dead lost as to what to buy.

Dave in Texas on Thu November 05, 2009 6:18 PM User is offlineView users profile

A least, and prolly more than, 10yrs ago I installed a Honeywell CT3200 to control my HVAC. Honeywell has always been the best 'controls' company.

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At 2, I went home with a 10. At 10 I woke up with a 2 !!

bohica2xo on Thu November 05, 2009 11:21 PM User is offline

Nick:

I have a pair of White Rodgers 1F90 thermostats in my home. They are at least 10 years old now. Been very reliable, accurate units. Batteries are a backup device, the unit "steals" enough 24v power to run without them. Programmable, the clocks keep accurate time over years. I am sure they have been superceeded by now, but I would not hesitate to use W-R units again.

B.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Fri November 06, 2009 6:22 AM User is offline

Local Shopko store is selling the Honeywell RTH heating cooling digital thermostat for $6.24, tried one, but was 3*F off in the thermometer part, took it back and got another, this one was 4*F off. Called Honeywell, suppose to be within 1*F of the actual temperature, but said I couldn't return it to him, just take it back to the store. They had more left, but got tired of chasing back and forth. This thing ran on two AAA batteries and no heat if they die, but figured I could steal 3 VDC off the 24 VAC line with a tiny VR circuit. These things use some kind of a stepping relay for the R-W, R-Y connection that are only pulsed to conserve on battery life, suppose to last over a year.

So I laid out 44 bucks and got a Honeywell, CT8775C round digital that is powered off the 24 VAC line, far superior quality, the thermometer is dead on compared to my NTIS thermometers so think I will install that one. They are stilling ground current through the gas valve, AC contactor, or the manual fan relay and only pulling 0.8 ma that is not quite enough to energize these valves or relays so only a four wire thermostat cable is required, but using a five would be no problem for me. The RTH's were software programmable, this one uses DIP switches that are far more robust. I may play with my old mercury, do have a spare heat only with flexible wires on it, but can't find a mercury anymore. Can't seem to find any White Rogers around here, just some strange made in China brands I never heard of.

Biggest surprise I got yesterday, was my gas bill, last month they charged me $1.27 a therm, this month it dropped to 82 cents per therm, but only had my new furnace in for a couple of weeks now so really can't compare the usage. It was a crime they shot up our gas bill based on OPEC prices, natural gas is 100% domestic and we are suppose to have a known 4,000 year supply of the stuff.

Can feel the air in the home is much better in that this new furnace is not burning up our oxygen supply and doesn't seem to run nearly as long. My old furnace went on with a loud click, this one is dead quite.

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