Trane Mod# TZEMT400B22 Odd Panel Behavior

Other Devices & Integrations Climate Control & Temperature Sensors
1

Model: TZEMT400B22
Ver:01.00.10
ZVER:02.006
ZHID:01.48eF.e7
ZNID:002

After being in use for a year, my Trane is exhibiting a strange behavior.
During normal run times, the thermostat would cycle and the only LED to come on was
the “Run” LED. The panel did not light up and the "POST screen did not show.

Now, the LED’s for; Sys OFF, Econ, Hold, No Msg. and the display panel, which is showing
the Trane Logo and ZWAVE logos are lighting up EACH time the heating cycle comes on.

As far as I can recall, this “POST” display, would occasionally show, when the thermostat
was starting a new Scheduling period, ERGO - 7:00am to 11:00am. Then again when the next
period was starting, 11:00am to 3:30 pm and so on.

Why is the POST screen, now, after a year, showing each time it cycles?

2

If it’s only happening when energizing a relay, sounds like a momentary loss of power.

Have you checked all the wire connections & pin connections for the T-stat to sub-base are clean and tight? Is the transformers power output good and stable?

JOD.

3

JOD,
Thanks for the reply.
Yes, that’s the first thing I checked. My electric supply is from a rual co-op and it does dip from time to time to 99 volts and I have my computer equipment on a UPC power supply because of it. Vera is also on this supply.
This setup has been the same for about a year now and the displaying of the POST information on the thermostat panel is new. At least for the last week.

4

So you measure something around 24V AC at the t-stat between C and RH?

5

These T-Stats do occasionally break as well, so don’t rule that out.

I came back from vacation a yr ago to find that one of my Trane’s was “misbehaving”, and needed to be replaced.

6

I’m with JOD. Sounds like your low voltage transformer in your heating system is losing power briefly when the system tries to cycle on. Could be a weak transformer, or one of your relays or contactors is pulling too many amps on startup. Could be bare wires shorting together occasionally, mice, dogs. These things can be a nightmare to find sometimes.

What kind of heating system is it? Gas furnace, heat pump, other? It may be time to call a service guy to look at it.

7

Given the above notes, maybe bench test it with a separate power supply and see if you can reproduce the issue?

8

Thanks for the replies;
I have checked the transformer supply and it is showing 24 V, but thats not to say it isn’t failing. I have had to replace it once already (system is 20 Yrs. old)
I don’t have any way to monitor the 24v supply constantly so it is just a “spot” check.
As of Monday day times, the Trane panel was doing just the green “HEAT ON” LED, no POST readings. Monday night it was back to doing the POST reading.
Today, Tuesday, it is doing just the green “HEAT ON” LED, no POST readings. Which leans toward it being a PM night time thing, I’ll note that tonight and see if it is a nightly thing.

EDIT:
After ignoring the better half’s stares, I camped out on the Trane’s panel and noted when the green “Heat On” LED was on and when the panel did it’s full “On” POST screen.
What I found was the “HEAT ON” lED was when the thermostat was calling for HEAT and the Full Panel “On” “POST”, was when the furnance had just finished up running a heat cycle and the blower then came back on to clear out the residual heat remaimning in the heat chamber.
This is a 95% efficent furnance, with the PVC exhaust pipe (condensating furnance)
My theroy is the wife has closed off some registers therefore blocking off the air or the filter is dirty (40 days use) and is blocking off the air. Both will cause the heat exchanger in the furnance to heat back up and trigger the blower to come on and get rid of the heat.