AUX Heat on 2 much, HW RTH8500D Stats, Trane XR12 HPs

[adcgroup]

I have 2 Trane XR12 Heat Pumps (a 3 Ton and a 2 Ton) each controlled by Honeywell RTH8500D 'Vision' digital programmable thermostats. I have the thermostats Locked In 24x7 at 69 degrees downstairs and 70 degrees upstairs. (I have no programed features active at the moment until I get this all sorted out and know HPs don't like to keep moving temps up and down)

We just moved in December and got a high elec. bill after 22 days. I decided to watch the meter and noticed that we were using a lot of electricity and noticed that the "AUX HEAT" was running a lot more than I thought it should.

I came home yesterday around 2pm. The outside temp was 60 degrees. I have my thermostats set at 69. When I went upstairs, the first floor unit was not running. Both ambient and setpoint temps were at 69. When I came down, ambient temp was 69, setpoint temp was 69, and the "AUX HEAT ON" indicator was on and the unit was running (of course).

I know that the AUX HEAT should not be kicking on and I'm sure it was not defrosting. I called the HVAC installers and had them take a look at it. They, of course, blamed the thermostats (since I requested to have them put in - they had the old ugly manual ones originally) and then the builder. "Digital thermostats never work right!", and the builder didn't put enough insulation on the kneewall under the house. He categorically told me that *both* digital thermostats were defective and I should replace them with good 'ol manual ones.

Now, what he said may be true, but it's also just what I'd expect him to say - just like I'd expect the builder to blame Honeywell and the HVAC installer and I'd expect Honeywell to blame the HVAC installer and builder. It's a vicious cycle of CYA.

How can I tell what's the problem? I see a lot of pros on this board who seem to like the digital stats. Our old house had Honeywell digital (non-programmable) stats, and we never had a problem staying comfortable or having a high bill.

Any ideas how I sort out what's really wrong?

Thanks,

Duane

[docholiday]

The thermostat itlef is not the probelm, the configuration and wiring are probably suspect but no one here will know for sure without looking at it, there are umpteen million ways it could be screwed up.

[mark beiser]

If the installer is so in the stone age that he puts manual thermostats on by default, and recommends them over digitals, I highly suspect that he didn't get the thermostats configured properly. They could also be wired incorrectly.

Do your outdoor units run in the heating mode? If not, he may have just slapped them on the wall and left the default setup options in place. The thermostat has to be configured for the type of system it is running, I think there are something like 11 system type options...

[Special Ed]

Whoever that stone-age A/C contractor is didn't configure the too-technical-for-him t-stats right.

[centralflinstaller]

wow..can't wire a t-stat,let me guess lowest bid ????

[chilledcool]

I would have to agree with the doctor and beiser.
Check to make sure the outside unit is running when the thermostat is set one degree above inside ambient temperature in heat mode. At this setting only the heatpump should be running and no aux heat.
If the outside unit does not come on but the aux heat does and/or the heatpump comes on along with the aux heat then I would say it is a wiring or set up problem with the thermostat due to improper installation by the installer, especially if both systems have the same trouble.
Call out another contractor that is not afraid to read the instructions that came with the stats.

[adcgroup]

You're all echoing my sentiments to a tee! The service dude had a thing against Digital stats from the very beginning. The very first words out of his mouth when he saw them were negative. I expect them to blame anything but their install, but he was relentless. Anything that happened out of the ordinary all afternoon pointed to the "finicky", "erratic" behavior of Digital Stats.

The contractor is who the builder chose as installer. We came along a little too late and the house was already standing. My wife loved it and the location, so you know the rest of the story.

While he was here, I had him pull the stat so we could check the wiring. According to the 'colors' and the install manual, the wiring is correct. These guys have been in business a long time, so I would ASSume the wiring at the HP is correct - at this point, anyway.

I've also dug around a little and found some programming info for the Honeywell Vision Touchscreen (RTH8500D) and it doesn't seem there's much to configure. It appears in the "Installer Setup", you can select date/time, type of system, changeover mode, Temp display (C/F), Daylight Savings, Filter change reminder, Adaptive Intelligent Recovery, and 12/24 hour time format. That seems to be an all-inclusive list for this model. I've checked the settings and they seem to be ok as far as I can tell.

----New Info----
This bit of may make a difference, but I don't know how significant it is given the problem at hand. In talking with the service dude after his checkup, he mentioned that the heatpumps were "slightly" overcharged. I asked him if that would make a difference and he said that it would cut down on the efficiency, but shouldn't produce the AUX HEAT problems I've been having. Anyone have a different take on that?
----------------

Now, to answer Chilledcool, the thermostat does kick heat on when set to one degree above ambient. Here's a breakdown of how it seems to work as I observed specifically today.

Setpoint = 0 (same as ambient) - unit sometimes kicks on - I'm assuming that may be the result of fractions of degrees? Perhaps it shouldn't kick on at all - that threw the service dude for a loop and added fuel to his "Get rid of Digital stats" fire.

Setpoint = +1 - after a few seconds, heat kicks on

Setpoint = +2 - Heat kicks on or stays on

Setpoint = +3 - AUX HEAT kicks on


If we go back to yesterday, however, I had the AUX HEAT indicator on when BOTH ambient and setpoints were at 69 - and it was 60 degrees outside. What might cause that if we ASSume the stat is wired and configured correctly?

As far as I know from the service dude, the Tranes are running as they should. He supposedly checked everything at the outside unit and it was ok. He recovered "some" freon from each of the units to bring them down to the recommended levels according to the paperwork inside the unit panel.

If Heat Pumps and stats are A-OK, what's next?

Thanks again!

[adcgroup]

For what it's worth, here are the exact words the service guy used on the work order to describe his findings.


"Evaluated system. Checked refrigerant level, a little overcharged. Recovered some freon. T/Stat does not work same all time. Heat strips comes [SIC] on at times when both ambient and set point are same. Recommend close vents in crawl space, all are open. Knee wall is not insulated. Temp is cold under house. Recommend replace those t/stats w/ Trane manual ones."


NOTE: Today, here in NC, it was almost 70 degrees. The vents are automatic, which is why they were open on a warm day. It was cold under the house in comparison to the sunny 70 degree day outside. He is correct in that a knee wall is not insulated. Our house is hardiplank and stone, so there is a block footer and about a 3 foot kneewall on top of that before you get to the sill plate on 2 sides of the house. The floor is insulated, however, and it looks to be about 6-8 inches of insulation - I couldn't tell for sure and couldn't find an R value anywhere.

[docholiday]

I havent used them much but from reading here, those a great thermostat. Sometehing isnt right here, Im not sure what tho.

[travisfl]

Originally posted by adcgroup
Any ideas how I sort out what's really wrong?

I'm surprised that your builder / contractor installed the Vision Pro retail version as opposed to the trade version. Did they buy it at Home Depot?

Anyway, check and make sure that Adaptive Intelligent Recovery option is set ON (see p.36 of your Owner's Manual - installer option 0530=1). If that isn't the problem, then there are a number of Trane system options that could be configured wrong, and you'll need to get a cooperative, professional contractor to fix it.

[adcgroup]

Well, they had originally installed manual stats. My wife didn't like the way they looked and I really wanted something that I could program to save elec costs. I asked the builder to have the HVAC contractor to change them out and they didn't want to, so we finally settled on me picking out what stats I wanted and they would do the install. I did my homework and came up with a lot of kudos for the Visions. I called the HVAC contractor and asked if there would be any problem with them. The guy I talked to there said that they could install anything I picked out as long as it was compatible with a heat pump. I asked if they could get them at a better price than I could, and he said I would probably do just as well picking them up at Lowes or Home Depot. So, I went to one of them and picked up a couple retail models and they installed them.

As far as the A.I.R., that option is set to ON.

When you say "Trane system options", are you talking about settings in the stat, or at the Trane unit itself?

My challenge, should I not be able to figure this out, is finding a "_Cooperative_, professional contractor" to look at it

Thanks

[travisfl]

Other than Adaptive Recovery and the System type selection (option 0170=7) there aren't any other options on the 'stat to configure. There are some wiring and configuration options on the Trane systems that affect the way the heat strips work, but they are not user configurable.

[bornriding]

Are you sure these are heat pump thermostats??
Did not find where you said anything about an emergency heat mode?? Which takes two-stage thermostat for heat.
Some of the programmable thermostats have an adjustable differential setting. Maybe this one has been programmed for a tight differential between the first stage heat & the second stage heat ?

Just a thought

[adcgroup]

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!

[chilledcool]

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?

[adcgroup]

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.

[trbleshootr]

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

[adcgroup]

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!

[travisfl]

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.