AUX Heat on 2 much, HW RTH8500D Stats, Trane XR12 HPs - Page 2
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  1. #14
    Join Date
    Feb 2005
    Posts
    7
    Yes, they are Heat Pump thermostats equipped with Em. Heat mode.

    They are Honeywell Vision Touchscreen model RTH8500D.

    They are also designed to work with other heating/cooling systems as well. The type of system is configured in the installer setup which I have confirmed is properly set for a Heat Pump.

    Can anyone tell me what would be the effects of overcharging the freon in a system? Would it ever produce a level of inefficiency that would cause the AUX HEAT to constantly supplement the heat pump?

    The more I think about it, the more I realize that the heat pump compressors were running a lot. From the electric bill, the AUX Heat must have been running a lot too. Yet, we were never too hot and the temp never went above the setpoint. It would seem to me that if the heat pumps were producing sufficient heat and the AUX Heat came on as well, it would shorten the cycle causing the heat pump compressor to run much less overall. I recall everything running quite a bit leading me to believe that perhaps the heat pump wasn't producing enough heat so the AUX Heat legitimately had to step in to keep the temp up.

    How likely is that scenario?

    And, if that's the case, would the overcharged compressors be likely to blame, or do I need to look for a different problem?

    Thanks!

  2. #15
    Join Date
    Sep 2004
    Posts
    265
    Aux heat should only come on when the set point is 2-3 degrees above the inside ambient temperature or when the heatpump is in the defrost cycle.
    If the heatpump is in the defrost cycle the larger of the two copper lines going into the outside unit would be cool, meaning the unit is in the ac mode which is correct for the defrost cycle. This would last only a few minutes depending on where you live and the amount of frost built up on the outside coil. When the heatpump is functioning in heat mode the larger line will be very warm if not hot to the touch.
    There may be an outside sensor on the heatpump to let the defrost cycle know when to terminate. If this sensor is not making good contact it will keep the unit in defrost.
    Are both units acting the same way or just one?


  3. #16
    Join Date
    Feb 2005
    Posts
    7
    Both units are acting essentially the same. I'm in the Raleigh, NC area, by the way.

    It could be by a freak of nature that I caught the unit in defrost mode the other day. It was 60 outside and 69 inside (setpoint & ambient). Would it have gone into defrost mode under those circumstances?

    It seems that whatever is wrong is wrong on both heat pumps. If it is the thermostats, then they're both bad. Ironically, *both* heat pumps were overcharged when the service guy came out.

    Would overcharging have this effect, though?

    We are supposed to have a cooler weekend. Since he took some refrigerant out, I'm going to keep a close eye on it. If the AUX HEAT doesn't come on, then I guess it must have been the overcharging.

  4. #17
    Join Date
    Nov 2004
    Location
    central ca.
    Posts
    11
    I installed an Amer. Std 12 SEER H/P sys several years ago and it had exactly the same problem. With the stst recommended by the supplier the 2nd stage was leading the first stage to a degree that aux heat was coming on instead of 1st, I was actually able to watch the mercury bulb moving.Wierd. I used 4 different stats before one would work with this instllation. They are service agreement customers and I check the sys. twice a year since, no problems at all. So check the heat anticipator votage, hopefully before messing with the unit charge.Just a thought and good luck

  5. #18
    Join Date
    Feb 2005
    Posts
    7
    Well, I felt compelled to discuss my dilemma with the builder who in turn called the owner of the company that installed the system. He and his partner are coming out on Tuesday and promise a complete inspection from top to bottom to get this resolved.

    There are a couple of things I need help with. Can anyone give me either questions I should be asking or things I should be looking for them to do to make sure that they have examined the system thoroughly?

    Second, I asked the owner what his opinion of Digital Thermostats was. He said he had no problem with them, but I want to be ready anyway. The only part of the system that I had anything to do with was the thermostats. On one hand, I think they intentionally had me pick them up so they would have a scapegoat if anything ever went wrong with the system. They DID install them, though. I would think that puts a little onus on them if they're defective. My thermostats are retail packaged Honeywell Vision Touchscreen models (RTH8500D). I had several people recommend these thermostats, but where might I find good information or additional recommendations that I can use in support of my choice when I talk with the installer?

    I hope they are truly coming to fix things. However, I am preparing for them to look at everything and say that 'my' thermostats have caused the whole problem and may have permanently injured the system and caused long-term damage that voids any and all warranties (after which they'll have to talk it over with my lawyer). Maybe I'm a sceptic, but I always say "Hope for the best, but prepare for the worst!".

    Thanks!

  6. #19
    Join Date
    Jan 2005
    Posts
    340
    Originally posted by adcgroup
    I am preparing for them to look at everything and say that 'my' thermostats have caused the whole problem and may have permanently injured the system and caused long-term damage that voids any and all warranties
    Outside of blowing a fuse, I can't imagine any scenario where a properly connected thermostat (even if defective) would cause permanent damage to a modern day heat pump system.

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