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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8768
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I had two technicians from the same company come out and

Customer Question

Hi!
I had two technicians from the same company come out and they think the problem is my new Exobee3 that I put in this last May. Just would like a second opinion, if possible, please :) .
I have a Trane XR13 heat pump, XV80 gas furnace and of course, the Ecobee3 (my previous thermostat was a XR402, I believe). Before I installed the Ecobee3, never had this problem (at least as far as I know - maybe not this last spring also after the Ecobee3 was installed). Anyways, ever since I started putting the heat on the heat pump a few days ago (this fall), what will happen is that the heat in the heat pump will run for about 24 hours... then after roughly 24 hours, when the thermostat will call for heat from the heat pump, the furnace will ramp up the but the heat pump will not run. No fan, hum, noise, anything from the heat pump - just dead (it'll run just fine cool mode, though)!
The tech guys came out too look at the heat pump, says that everything checks out on it... says that the TXV valve is good, pressure is good, refrigerant is good, temperature is good, signal is coming to the heat pump board for heat, signal light on the board, not frosted up, wiring looks good - but nothing happens. What we discovered (along with the tech the day before - he wasn't very sure about the results that day) - the only way we can get the heat to come back on the heat pump, is if we turn the thermostat to cool from heat after the heat pump is dead (after being in heat mode), it'll run in cool (like mentioned above, no surprise), then switch it back to heat and the heat pump will run! It'll run in heat for 24 hours (about) until the heat pump dies again... have to switch it to back cool, then back to heat and it'll heat. Wash, rinse, repeat.
I have a replacement Ecobee3 coming soon (hopefully :p ~)... but my main question - does this truly sound like a thermostat problem or could it be something else that is being missed??? The head tech thinks it's a bad signal form the thermostat that's causing the heat pump to die/turn off.
Thanks much in advance!
Submitted: 2 years ago.
Category: HVAC
Expert:  Phil replied 2 years ago.

Hello,

The XV80 furnace has a variable speed blower that works in conjunction with the two stage gas valve and other features... the ecobee is not designed to accommodate the variable speed features...nor what is a proprietary Trane controls system in many aspects. Trane has their own line of remote controlled wifi thermostats that you must buy to get that sort of wifi and variable speed performance.

https://www.trane.com/residential/en/products/heating-and-cooling/gas-furnaces/xv80.html

..........

Please remember to rate my service before you leave today. It is how I earn a living, and does not increase your charges.

If you need anything else, just let me know. You can continue asking follow-up questions at no additional cost.

Customer: replied 2 years ago.
Hi!Thanks for your reply! The jumpers on the XV80 is set to run in comfort-r mode and the Ecobee3 is set to let the HVAC system control fan speeds (instead of the thermostat)... as far I can tell, during the summer (cool mode), the variable speeds were working just fine on the furnace... (if I remember right) 1 minute slow ramp-up to dehumidify, 7.5 minutes at 80% fan speed, 100% thereafter and 3 minutes ramp-down for air flow... also, the dehumidify feature worked just fine at a slow fan speed... so at least when it's cooling, it seems like it's working. When the gas furnace is on, stage 1 has a slow ramp-up and a slow ramp-down. We haven't got quite cold enough to hit a stage 2 but it works just fine with the highest fan speed in test mode on the Ecobee3. When heating on the heat pump, it's delayed ramp-up and slow ramp-down. I haven't heard a defrost call on the heat pump yet - but the tech says that it's not cold enough for it to do it yet. Do you think the heat pump is calling for a defrost and the furnace is confused because of the thermostat??? Like I say, it seems like the variable speed features are working fine, but I'm not an expert, so I'm not positive what's going on :p . On the RMA form, the Ecobee folks put down that it's a relay is fused (all of this was over the phone, though ~_~ ).Also about the preparatory stuff that Trane has, I know that one is the outdoor temperature sensor, so that's not currently hooked up... the Ecobee3 is getting the temps off of wifi, so supposedly it should know when to cut the heat pump off and allow the furnace to run :p . Currently, the heat pump cut-off temp is set at 25° (we haven't reached that yet). Not sure what the others are and the furnace cut-off is 50°.Anyways, after all of the above :p , curious if you have any additional thoughts :) . Thanks again ^^ !
Expert:  Phil replied 2 years ago.

Hello again, thanks for the detailed explanation.

Defrost is normally a separate and independent function from the thermostat, without an extensive study of the electronic controls I cannot say for sure that the defrost is confusing the furnace or the thermostat. Some systems energize one of the electric resistance heaters during defrost... that would not confuse the type of thermostat you have, and should not confuse the furnace controls.

Your ecobee folks were not too far off with their diagnosis that a set of contacts in a relay might be fusing...that might be in the 60% accurate range.

Do this test, next time the heat pump is stuck in heat pump mode, AND the largest copper tube attached to the outside unit is hot (that is important to notice, it confirms the heat pump compressor is actually running).... AND the house is more than 2 deg F warmer than the thermostat set point as a result, remove w1 and w2 thermostat wires from where they attach to the printed circuit card inside the furnace... tell me if the largest tube attached to the outside unit cools off or not.

IF the tube does not cool off, remove the Y1 wire from the same terminal strip... be sure not to short any of these wires to C or ground them on the frame of the unit.

We can go from there.

Customer: replied 2 years ago.
Hi!When you say stuck, you're talking about when the heat pump is dead, right? I'm pretty sure the tube hasn't been hot in the past... the temperature actually sags below the set-point and never comes up (the furnace fan can run for a couple of hours cold until I catch it - unless I notice the air is colder than it should be earlier)... when I rectify the situation, the temp comes up in just minutes. Anyways, I've set the thermostat back onto the heat pump (off of aux heat - it only took an hour this afternoon before the heat pump was dead :p )... when it does it's thing again, I'll let you know what I find out. May take up to 24 hors (sorry ~_~ ), but as I have learned, it only took an hour this last time :o .~Just for clarification - if the tube is cold, I probably don't need to continue with the wire test, do I (I'm getting not)?Thanks again and for your patience :) .....
Expert:  Phil replied 2 years ago.

When I say 'stuck' I am referring generically to any number of relays or switching devices in the furnace relative to that circuit... we will get into more detail later, if needed, as we progress with the trouble shooting.

If the largest tube attached to the outside unit, the one that is insulated and a bit larger than the size of a mans thumb, then the compressor inside that unit is not operating... the tube runs hot in heating mode and cold in cooling mode.

If the air filter in the furnace is dirty, the heat pump coil attached to the furnace will over heat and trip the high pressure safety cut out mounted in the outside unit.

Make sure the air filter is clean and none of the air vents are closed off.

You do not need to do the wire removal tests if the tube is not hot.

I also need to know how old the system is, and if you have furry pets in the home, that can clog the heat pumps A coil, above the furnace in a few years.

Customer: replied 2 years ago.
Ok, W1 & W2 removed, tube hot, heat pump running. Y1 removed, tube cools off, heat pump does not run.Filter is changes once a month... should be clean :) (hopefully >< ~). Never had a dog or anything else with this system except for a Chinese hamster currently :p ~.....
Expert:  Phil replied 2 years ago.

Thanks for the tests, so far it does not sound like an ecobee problem to me, at this point I don't think I can heip you from here, it is going to take a real sharp tech on site with instruments to sort that bug out, a very tall order for anyone.

I will opt out in case one of the other experts here has seen and knows what to do about this problem.

.

Customer: replied 2 years ago.
Hi!I'll repeat the test again tonight... when I took the Y1 wire off, the furnace also didn't ramp up so I'll see if I accidentally missed something somewhere. I'll let you know if it does the same or not. Hopefully I missed something :p .....
Customer: replied 2 years ago.
Hi again,Yeah, I repeated the test again with the same results. Disconnected W1 & W2 coming form the thermostat and the heat pump works / fan speed ramps up. Disconnect the Y1 along with the W1 & W2 wires from the thermostat and no heat pump / no fan ramp-up.Looking at the wiring on the furnace, this is how it is wired (the tech yesterday said it was ok):
Thermostat wire -> / Furnace terminal / <- Heat Pump wire
arrow=wiring going to lettered terminal on furnace; 0=no wire:
-> BK/TWIN 0
-> W2 0
-> W1 <-
-> R <-
-> G 0
-> B/C <-
-> Y <-
0 YLO 0
-> O < ... good thing my gas company will replace whatever's wrong for free (well, with a monthly fee - Service Plus :/ ).......also, I was wrong earlier - the heat pump and furnace was installed at the very beginning of 2007.Anyways, thanks again for all of your help and hopefully somebody else might chime in here soon ^_^ .....