Home thermostat question

By SNGX1275 ยท 6 replies
Jun 3, 2011
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  1. I know this is a longshot here, but figured I'd give it a try:

    So I bought a honeywell non programmable thermostat to replace an old honeywell round one. I wired everything up the way I thought it should be, but the AC stays on below the set point. So if I set it to 76 it continues running below that without shutting off. It does turn off by flipping it from Cool to Off.

    Old thermostat: http://img818.imageshack.us/img818/4601/img0176ix.jpg

    New thermostat: http://img845.imageshack.us/img845/4568/img0179g.jpg

    I called Honeywell on it, and the dude basically said there is no problem unless it does this 14 days later. He was saying they have a 14 day learning period. I think it not turning off several degrees below the set point is an actual problem and not some learning period. I can't see how the wiring could be messed up... There is a jumper to switch on the back if you have a heat pump and some other form of AC, but this is on a regular electric and normal AC unit. Although I may switch the jumper anyway..
  2. jobeard

    jobeard TS Ambassador Posts: 11,165   +986

    IMO, the heat pump choice would be wrong - - that's special stuff and most A/C is not like that -- could be, so inspect the evaporator label.

    I have a unit that has a learning curve, but that learning is to adapt the start time so that the room gets up to the set point in the morning when you wake (ie on the heat cycle, not the cool cycle). I've used the installer instructions to disable such learning and make the thing just obey :)

    I read your post to say that when the room reaches the set point, it overruns and when it does stop, the thermostat then actually reads +2degrees. While the readings of a thermostat are not calibrated, the on/off actions should occur at the set points selected.
    It may take ~1 minute to purge, but that should not overrun to +2.
  3. SNGX1275

    SNGX1275 TS Forces Special Topic Starter Posts: 10,742   +421

    Today it got to 79 in the house and I kicked the unit on, with a set point of 78. Then I forgot to shut it off when I left the house for a bit and it got down to 74 by the time I got home. So even with a +/- 2 degree allowance this still misses.

    I too did not think it was worth switching the jumper because I know I don't have a heat pump.

    We have a separate unit for upstairs that got replaced last fall (we rent) and it replaced a honeywell round, but that one did not control any heat. I may look at its wiring, although it is a different thermostat brand, just to see about how the A/C is hooked up. That might not tell me anything, but in the spirit of further troubleshooting I may look up its manual online and see if I could swap it for the honeywell that I'm having issues with. Although that may not work either because the upstairs one may be an A/C only thermostat..... I'll check tonight.
  4. jobeard

    jobeard TS Ambassador Posts: 11,165   +986

    The following *may* be due to my configuration but . . .
    the thermostat must be coordinated with the controller.
    My system is two zoned, where there are two thermos, controller, one A/C-heater, and two independent duct works. Zone one controls multiple rooms in 1/2 of the house and the other zone takes the remainer. The multi-zone controller board must be married to specific thermostat types, mfg and model.
  5. Zen

    Zen TechSpot Paladin Posts: 861   +50

    I know that this might be of no real help here, your owners guide probably has all this stuff in it. But I did find a handy installation guide as far as hooking up a Honeywell RTH1100B Horizontal non-programmable thermostat. The link I'm providing is in ((PDF)) format. I hope at least some of this helps.....


    Good luck to you :)
  6. SNGX1275

    SNGX1275 TS Forces Special Topic Starter Posts: 10,742   +421

    In my setup they are completely separate.

    I'm going to Lowes to see if anyone there knows (highly doubtful), but Honeywell support isn't very good. I haven't swapped with the upstairs thermostat yet, but I did pop its cover off and its a heat and AC thermostat (was concerned it may be AC only). The wiring is really straight foward on it and has the same color scheme. Once Lowes convinces me they don't know anything I'll take the upstairs thermostat and hook it up downstairs. If it shuts off the AC at the right set point then I'll take the Honeywell back to Lowes and get a different one. If it doesn't, guess I'll be calling a HVAC dude.
  7. SNGX1275

    SNGX1275 TS Forces Special Topic Starter Posts: 10,742   +421

    Update: Swapped the thermostats and ran into the same issue, so I think the problem is more serious than a simple thermostat problem. I don't really know how something could have gone wrong, I had the breakers off before I did anything and the old one worked, but you had to physically depress the switch for Cool - otherwise it would go to off.

    Guess I can try and clean the contacts on the old and see if it still works, will have to try to clean the contacts.

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