Trane airhandler invaded by gremlins

[kokopup]

We have a brand new heat pump system, Trane XL16i heatpump with Trane variable speed airhandler (4TEE3F40A1000AB--the guys who work on it refer to it as "the 40"), Aprilaire humidifier and programable thermostate.

Approx ten days ago, as heat pump was in recovery stage moving from sleep to wake mode (60 to 68 degrees), air handler/blower began switching on and off, but would work fine if we switched to emergency heat. Thermostat would "buzz." Installer replaced the circuit board.

Everything worked fine for one week, then same problem at same time, but this time air handler would click on and off without blowing any air at all. Again the buzzing with the thermostat. After hour, hour and half, could run on emergency heat for short periods of time before problem started again. This time they replaced the "module" (modulator?) on the motor.

Worked fine for three days, then same problem, except no blower action at all, even on emergency heat. They swapped out circuit board again--no improvement.

Service guy is stumped and is calling Trane tomorrow. Has anybody else run into this? He said he's never seen this before. These guys are good and have been very responsive to service calls. They just seem quite perplexed.

In the meantime, he hotwired a regular blower motor (ie., not variable speed), so it bypasses cicuit board and is running all the time. A temporary measure to give us heat.

[mark beiser]

Never seen that kind of problem before. What kind of thermostat do you have? I have seen some power stealer thermostats cause some very odd problems.

On another note, you let it drop down to 60, then recover to 68 inside the house?

Do a search on the site for "hetpump setback" for more detailed info, but with a setback that far, you are costing yourself far more money recovering the house to 68 than you save by letting it set back to 60. Keeping it 68 would be less expensive than what you are doing now...

[airconman]

could be something with the thermostat..... usually if wired wrong you'll blow the 3 amp fuse.
Air handler wiring is pretty straight forward... hmmmm have to do some scratchin on this one, have seen em smoke before but thats usually on fossil fuel kits if someone hooked up wrong....

[kokopup]

Mark, we actually like cooler temperatures, and have a hard time sleeping if it is much above 60 degrees in the house. In theory anyway, our thermostat has a program in it that slowly raises temperature so that auxillary heat does not kick in. Isn't the resistance heat what costs money? Pe ryour suggestions I'll search archives and see what they have to say on the subject.

Airconman, I checked wiring myself and it does look pretty straight forward. But I am suspicious of the thermostat, given that all else on the airhandler has been replaced. I just haven't been able to interest the service guy in this theory. Maybe he'll learn something today from Trane. (It is also a Trane thermostat.)

[mark beiser]

Ok, as long as you are not doing the huge setback to try and save money like some people do. Comfort is king in my book. Do what makes you comforterable. The energy companies, government and to some extent, manufacturers, seem to have forgotten that these are COMFORT SYSTEMS.

I'm interested in what Trane thermostat you have. Does it look like the one pictured at the page the following link takes you to?

http://www.trane.com/Residential/Pro...grammable.aspx

If so, have them replace it with a better thermostat, even if you have to pay for the upgrade. I have found many many of that style thermostat to have wierd problems, regardless of what name it is sold under. It is Honeywell's cheep line of digital thermostats.

This one would still be covered under your 10 year parts and labor warranty, if you have one:
http://www.trane.com/Residential/Pro...grammable.aspx

Or even better, a Honeywell Vision Pro.

http://content.honeywell.com/yourhom...ionpro8000.asp

[kokopup]

We have the Trane XT500C, which seems to look like the one on your second link, but the description of it resembles the one on your third link.

And while comfort is part of the equation, money is too. Am I wrong in thinking that it is the resistance heat that drives up the cost of swinging temperature on a heat pump?

[mark beiser]

The resistance heat is a huge part of it, but even if your resistance heat is locked out by the thermostat during recovery, you are having to reheat the house 8 degreese.

Considder that you have to reheat more than just the air. You have to reheat the mass of all the furnashings and walls in the house. Another thing to keep in mind is that you are asking the system to do all this reheating during the part of the day that the heatpump has the least heating capacity. During cold weather it is likely that the system is not hitting the new setpoint during the recovery cycle, in wich case it will bring on the auxiliary heat to get to the set temperature.

When the outdoor temperatures are below the ballance point for the system, the heat pump is not even able to maintain the set temperature without using auxiliary heat, much less heat the house up from a lower setback temperature.

I only set the temperature back on my system during the day when I go to work, and only from 68 to 65. In my area, I think we only have like 4 days every 3 years where the daytime temperature is below the ballance point though.

I always thought it was a bit ironic that, because heat pumps are sized for cooling, the parts of the country that need heating the most, have the least heating capacity from thier heat pump systems....

[Edited by mark beiser on 01-31-2005 at 07:49 PM]

[kokopup]

What is the "balance point"?

[billygoat22]

We had a similar problem awhile back- the Aprilaire on a Trane unit would cut in and out (solenoid) randomly every 30s or so, sometimes would do this, sometimes not, Can't recall if it was "fixed" permanently this time.

[mark beiser]

Originally posted by kokopup
What is the "balance point"?

The ballance point is the outdoor temperature that the house is loosing heat at the same rate the heat pump is able to heat the house.

Below the ballance point, the house looses heat faster than the heat pump can heat the house. The heat pump will run constantly, and the auxiliary heat will cycle on and off periodicly.

The ballance point is different fome home to home, but usually is in the low 30's to upper 20's.

[joker dan]

Ihave experienced something in the order of this before , low volt fuse would blow at different times could not isolate when it would happen .aloud hum was noticed before it did at the indoor unit. with the indoor breaker off iwas getting a small feed of voltage from the low voltage terminals to ground .my fluke meter will beep when this happens . turned out tobe the defrost board; when i removed it the voltage from terminals to ground disappeared.all has been fine since i replaced the board i hope this helps,it was an interesting problem