Thermostat mystery

[elcom]

I've learned so much from Garage Journal that my wife actually suggested that I post the question here...

I have two Trane XE80 forced air (conventional gas heat) units.
Last year, I installed two Honeywell smart thermostats -- which have been working fine until now.

We don't use the AC during the winter, but it is now getting warmer in Houston. Last week, I turned on the AC at the thermostat and it displayed "waiting for equipment." I can turn the fan on/off separately from the compressor and it works as expected. If I cross the red/yellow wires, the compressor turns on immediately.

Thinking that this meant that the thermostat was bad, I called Honeywell and they agreed. Got a new one from Home Depot, same thing. Replaced with another one --> same thing. Got a lower end Honeywell model --> same thing.

Every so often, but not predictably, seems to reboot.

Wonder if anyone has any ideas... Thanks in advance!

 

[Rockhead261]

Is there an Rc-Rh jumper or a way to configure the thermostat for a single system transformer? Sounds like it might be set up for two.

 

[JackDiddly]

Also there is generally a wait period on all newer digital stats that will keep the compressor from coming on for generally up to five minutes esp. honeywell. If you think its not working because you see WAITING it literally is just waiting for the set period of time before it allows the 24v signal to travel to the equipment and turn it on. wait five minutes, prob solved. look in the manual for the stats you should be able to adjust the length of time it waits. but I would recommend leaving them at five min.

 

[JackDiddly]

And, the fan will always switch separately if G is wired between the stat and the equipment.

 

[bonneyman]

Good advice all.

I really hate the modern electronic programmable stats. Too finicky, too fragile, don't like static shocks like when you walk across a carpet. Most made in China and are pieces of junk. I have customers go to the local home repair store and get sold a electronic wizard that will "cut your electric bill in half"! In less than a year they're calling me to help them out. If you hear this kind of sales pitch, RUN!
I was given a Honeywell touch screen stat a couple of years ago. Have had good luck with it so far. But it retails for $200+. Yikes! I keep an old mercury bulb stat in reserve just in case!

 

[elcom]

I have jumper between Rc and Rh -- removed it and connected the red wire to Rh --> thermostat does not turn off. Connected to Rc and it does the exact same thing "waiting for equipment."

Thermostat is set up for 1 stage heating and 1 stage cooling. Notably, just like the one downstairs that has been working fine.

Also, waiting more than 5 min. Still nothing. Just says "waiting for equipment." Fan works fine.

Puzzled...

 

[dw1]

Take the cover off to the outside unit, make sure nothing has moved in there and chewed on the wiring?? (Mice) when you changed the T-Stat, did you turn the power off? see if there are any flashing lights on the circuit board inside the furnace, the number of flashes would indicate what fault, check the fuse on the circuit board inside the furnace, Last- Cycle the power to the furnace and outside unit to clear any faults.

 

[elcom]

Thank you for the thoughtful suggestions.

Did not see any obvious defects in the wires outside, but will check again.

Did not turn off the power when I changed the thermostat, but the board was blinking slowly as it should indicating no fault.

Tried cycling the power with no effect.

One more thought: crossing the red and yellow wires *at the thermostat* turns on the compressor immediately. Which is why I changed thermostats 3 times.

 

[Rockhead261]

It's definitely the compressor protection feature locking the a/c out, and there's definitely something wrong since it's only designed to prevent immediate restart after shutdown, not a simple on-delay.

Pull the stat and remove the batteries, wait upwards of ten minutes, then reconnect and try again.

Can post up a picture of your subbase?

 

[elcom]

The thermostat has no battery.

I am attaching pictures of:

1) Thermostat face
2) Thermostat base
3) Control board (two pictures)

The board is old, but the indicator light is flashing normally. Also, when I cross the red and yellow wires, the compressor turns on -- therefore, does not seem like it is the board.

An identical setup downstairs is functioning normally. The only difference is that I disconnected the Rc-R jumper. Does not seem to make a difference.

 

[Rockhead261]

Amuse me and move the red wire from Rc to R.

 

[elcom]

I was interested in this as well, thermostat does not turn on with the red wire in Rc.

 

[JackDiddly]

So this one has had me scratching my head too, The honeywell smart thermostats that I have been seeing require a C or common between the stat and equipment, likely your old one did not ever have one, How did you go about hooking up your new stat with a C wire when you installed it did you "borrow" one of the other wires? Pics would help. also pics of low volt hook up in furnace. the fact that you can jumper everything on without hesitation each time I assume, says that either the stat is programmed wrong or its not hooked up correctly, you have 24v at R and are able to manually change it???
Another thing I thought of that would cause a delay on your a/c equipment is the utility company "Saver Switch" as its called out here that gives the utility company the power to interrupt the 24v signal to only the outdoor unit leaving the fan run inside. Often the intallation is offered with a discount on your energy bill. I do not like them.

 

[JackDiddly]

sorry missed the pics

 

[cort]

The picture you showed of the base of the thermostat stat looks like it is missing a jumper--the jumper that connects power from heating to cooling. Did you remove this jumper intentionally? Without that jumper, your system will not work correctly. Look at my photo below. This is how yours should look too assuming you don't have two transformers in your system--most people don't. Find your jumper, and reinstall it.

The lock out period on my Honeywell smart thermostat is more like 8 or even 10 minutes, not 5. It may be that you are not giving it enough time. If your base is hooked up like what I've pictured, and things still don't work, then double check you thermostat's configuration. Make sure it is set up as conventional heat (forced air--not heat pump), and single stage on both heat and air.

You might also verify system power with a volt meter. Even with the thermostat off the base, you should find 24VAC between the pad next to R and the pad next to common (blue), and there should also be 24VAC between the pad next to Rc and the pad next to common (blue).

 

[elcom]

Yes, removed intentionally. Was planning to put back. No difference in behavior.

I get over 24VAC (~28-29VAC) between the red and all other wires.

 

[cort]

Have you been able to get the stat to clear the message "waiting for equipment"? Until that message is gone, you definitely won't get any cooling from the stat. Be sure you are not in heat pump mode on the stat too. Wait a good long while between changeovers. 5 minutes may not be enough. At some point the stat ought to say that it is cooling assuming the stat's set temp is set at least 2 degrees below ambient temp. By then you should find 24VAC (28 VAC is close enough) across the stat's yellow and blue wires. From the pic it looks like your outside compressor unit has red and green wires on it. The outdoor unit's green wire is connected to common, and the outdoor unit's red wire is connected to yellow. Those 2 wires (outdoor red and green) should be energized with 24VAC when the stat is calling for AC.

 

[Zeke]

I had that t-stat for one day. Got rid of it and went to a more basic model that does NOT interface with the Net but does allow a remote t-stat to be used. I like that feature. I get that message now and then but it always clears in a few minutes.

 

[elcom]

Not in heat pump mode.
If the ambient temperature is above the set point, then I get a normal "cool on" message.

Re: clearing the "waiting for equipment" message.
I can remove the thermostat from the base plate, causing it to reboot.
Sometimes it reboots itself -- I thought that it might be caused by activating the fan (i.e., thermostat reboots when fan is activated), but not sure now.

 

[cort]

I can remove the thermostat from the base plate, causing it to reboot.
Sometimes it reboots itself -- I thought that it might be caused by activating the fan (i.e., thermostat reboots when fan is activated), but not sure now.

Your stat definitely should not reboot itself. What is it doing that lets you know it is rebooting?

Also have you switched the stat from heat to cool mode? If I recall correctly, this stat doesn't make that change automatically.

 

[elcom]

There is a visible reboot sequence. First the screen is blank, then "Honeywell" in red letters is displayed on a white background, then "please wait" on a blue background and finally, the home screen returns.

The thermostat is in cool mode. It can be configured to switch heat/cool modes automatically or set manually (I set mine to manual switch).

 

[Rockhead261]

Amuse me and move the red wire from Rc to R.

I was interested in this as well, thermostat does not turn on with the red wire in Rc.

Sorry, did I miss something? The pic shows the red wire on Rc. Was that only temporary?

 

[elcom]

Apologies -- you are correct, I have the red wire in Rc, thermostat does not turn on when the red wire was in R and the jumper was removed (as it is in the picture). I have since re-installed the Rc-R jumper.

 

[Rockhead261]

Apologies -- you are correct, I have the red wire in Rc, thermostat does not turn on when the red wire was in R and the jumper was removed (as it is in the picture). I have since re-installed the Rc-R jumper.

OK. Did you try installing the red in R and leaving the jumper in place?

 

[cort]

Your stat definitely should not reboot itself--ever. It should only reboot when power is taken away and then reapplied. But this is a separate issue from the cooling issue you described. Rebooting should happen only if you turn off the power supply. Are you sure the stat is fully engaged with the base plate when you push the stat on the wall? When you replaced the stat with a new one, did you replace the base plate too? It kind of sounds like a cracked circuit board on the base plate or a broken wire if the stat is randomly rebooting.

On another note, with your jumper installed, it shouldn't matter if your red wire is in the R or Rc connector, but verify voltage is present on both the R and Rc pads with respect to common.

 

[Rockhead261]

Good thinking on the base plate/contact with the stat.

My thoughts on Rc vs R were brought about by the possibility of any anti-backfeed diode on the Rc terminal that might be preventing the stat from seeing power under certain circumstances.

I'm pretty much tapped out at this point. Subbed for uodates/solutions.

 

[elcom]

Thermostat is pretty solidly attached to the base plate. Maybe something is not engaging, but then it is happening the same way with 3 different thermostats (3 different base plates) + one additional model with its own matching (different) base plate.

Voltage between blue (C, common) and Rc with the jumper installed is just under 28VAC. The red wire is plugged into R and jumper is installed.

I tried to replace the base plate, no difference.

I even tried a different model (still Honeywell wireless, though) which has a different base plate. Also no difference.

 

[elcom]

Not much of an update, but after leaving the system in cool mode (not running and temperature usually above threshold) for a while, the transformer burned out.

I replaced the transformer with a "resettable" model and the system has returned to its previous status; still not functioning.

I also tested the yellow wire (the one that goes from the thermostat to the board and should control the contactor on the compressor) for continuity with common (blue wire) when it was disconnected from the board and thermostat (i.e., testing whether there is a short involving the yellow wire) --> no continuity (i.e., no short).

Am trying to get our AC guy to come out to help, but he seems to be too busy for me .

 

[Milton Shaw]

Have you checked the wires for breaks. I would take a foot of cable and the tstat and go out to the unit and wire it in and see if it works. If so then replace the wiring. Also the wires inside the house furnace unit unit may be wired wrong and not the same as what you see at tstat or at the outside condenser unit.

 

[LS6 Tommy]

If you smoked a transformer, you have a short, too many loads or a very low impedance load somewhere...

Tommy

 

[Andyjman]

From what i have seen, alot of the honeywell stats make you wait in between cycles because they have no programmable dead band. I installed 2 of those exact stats at my house, and took them out the same day because i refuse to use a stat without an adjustible dead band. A programmable dead band allows you to ad a "dead zone" where the thermostat will not start the equipment. For instance, i have a 2 degree dead band set on both of the stats in my house. Basicially what will happen if i have the temp set at 74 degrees, it will have to get up to 76 in the space before the unit turns on. It prevents short cycling like if someone opens a door and walks by, the unit wont nuisance run. Sounds like honeywells solution to having a 1 degree deadband is using a time delay.

 

[Boyd]

If you smoked a transformer, you have a short, too many loads or a very low impedance load somewhere...

Tommy

Agree with this.

 

[elcom]

I like the suggestion of wiring the thermostat to the board with a couple of feet of wire. Haven't done it yet.

My AC guy suggested that I install a mechanical thermostat. I did that and it seems to be working. It does not use the blue (common) wire and so far has not damaged the transformer. He suggested that I wait approximately a week to make sure that there are no issues with the transformer that would indicate a short.

I would prefer a programmable thermostat. Therefore, if there are no issues this weekend, I will install a Honeywell. Exchanged for a new one just to make sure, though I don't think that there was anything wrong with the previous one I had tried.

Thanks for the suggestions!

 

[UncleDonut]

You said you have 2 systems. Are both not working correctly? Are you using 1 transformer for both systems or are they completely independent of each other?

 

[elcom]

Correct, I have two independent systems, each with its own thermostat. One (downstairs) is working correctly. The problems are limited to the other (upstairs) system.

 

[elcom]

So it seems like the culprit was the blue (common) wire. It was probably shorting (perhaps with the power wire intermittently). I disconnected heat (white wire) and used the white wire as common and everything worked -- seems to be working x 24 hours now. I can't turn on the heat, but it is not a big problem for the next few months in Houston.

Not sure if it is practical to change the wire. It is fed through the wall on the 2nd floor into the attic (3rd floor).

Thanks to everyone for your help!

 

[DC73]

So it seems like the culprit was the blue (common) wire. It was probably shorting (perhaps with the power wire intermittently).

As best you can, inspect the wires everywhere they are visible. You might get lucky and find the short. I had a similar problem one time. The AC Tech correctly diagnosed a short and then we set about trying to find it. The initial thought was we would have to pull new wire but, after looking carefully, we discovered that the plumber had set one of the legs of the water heater on top of the wire. The leg eventually cut through the insulation and created a short. It took a mirror and looking behind the water heater to find the problem.

Good luck.

DC