CT 100 thermostat

Our original upstairs CT 100 thermostat failed, so I installed a new one today.

I wired it exactly like the original was wired, and verified that against a picture I took of the original wiring scheme.

I configured the thermostat for a heat pump with auxiliary heat, and all circuit breakers were turned back on after the install.

But the thermostat doesn’t seem to be communicating with the heat pump at all. The thermostat has power and you can work the screen, but inputs at the screen don’t elicit a response from the heat pump. It won’t cool or heat, and the fan won’t turn on.

Any ideas about what’s wrong?

Pic of wiring would help.

check all your disconnects and breakers.

Breakers are all on and connections are tight.

The labelled wires.

R/RH is power
Y is first stage heat/cool
Y2 second stage cooling
W is AUX second stage heat
G is fan
C common (tstat power)

Verify proper wires are connected, as I see yours are not color coded (e.g., W is usually white), and verify all disconnects and breakers. Disconnects are usually at handler and heat pump.

Wires and ports are as follows:
Green: G
Red: RH
Yellow: Y
Brown: Y2
Orange: O
Blue: C

Manual says if you do not have both a B and a C wire, then choose the C port.

Those are the only wires the old unit had.

W wire?

C is common

If the old tstat didn’t have W then it may not have been for a heat pump. Depending on the type, W is either first stage heat, or second stage AUX/EM heat.

On a Aux heat pump, Y is almost always first stage cool and heat, and W is second stage heat strips (auxiliary heat)

In any event, if not working you need to check the disconnects, and meter the wires

I take it this you have an electric heat pump, and second stage AUX heat is heat strips?

Or is it something else?

Also, your RH and RC looks to be jumpered? Why is it jumpered?

What you need to do is verify each of your wires, not guess, but verify.

With multimeter touch RH and C, you should see 24V AC, if you don’t, find out why you have no power.

green G FAN
yellow Y (usually) FIRST STAGE HEAT/COOL
Orange O REVERSING VALVE (usually O)
W (usually on 2 stage HP) AUX SECOND STAGE/EM HEAT
Y2 If you have second stage cooling

Oh, and if Vivint wired the other tstat that you replaced, and that you are now trying to match the wiring for with the new tstat, then I can almost guarantee you that they wired improperly.

Chances are good, that it was installed as a single stage heat pump (seems to be the default on ADC), and probably never manually configured by the Vivint tech.

My suggestion is to contact an HVAC company that specializes in your brand, and have them wire your tstat and check your air handler inside unit, and outdoor unit board. If that tstat was/is improperly wired, you might be replacing more than just your tstat.

Here is how my electric AUX heat pump is wired

Yellow Y first stage cool/heat
Red R/RH power
Blue C common tstat power
White W second stage AUX/EM heat
Green G fan
Orange O reversing valve

Yes, it’s a heat pump with auxiliary strips.

I accidentally forgot to mention the W wire. It is black and is in the W port.

RH and RC are jumpered because I only have an RH wire (ie, no RC wire). If you don’t have an RC wire, the manual directs you to leave the jumper in so that the RH wire can provide power for both heat and cool.

Vivint did do the initial install, and I did duplicate their wiring scheme when I put this one in. But their tstat worked fine for a year.

The disconnects for the heat pump and the handler are both good, and the circuit breaker is on. The air handler has power because there are lights flashing on it. I’m stumped. I guess I’ll call the HVAC guys tomorrow.

My 2stage electric heat pump w/AUX is wired same as yours (minus Y2) and does not use RC.

Did you meter C and RH? Have you tried batteries in The CT100?

If you damage your system, its gonna be costly. On the average the inside unit for a heat pump runs about $10k, and the outside unit around $5k

Riven, your RH and RC are indeed jumpered. The small black jumper on the board below the wiring terminals does the same thing as the OP’s wired one. It even says RC to RH right on it :wink:

Ok. My bad. I didn’t pay attention to the jumper… so RH/RC jumpered…

I don’t have a meter for voltages as low as I am dealing with here. All I’ve got is a 90-500V/AC tester.

At this point I’m going to turn it over to an HVAC company, because I don’t trust Vivint and would like everything in both of my zones inspected by genuine pros.

Ok. My bad. I didn’t pay attention to the jumper… so RH/RC jumpered…

Yeah, that’s done do that they only need to run one power wire from the unit to the thermostats.

A multimeter is like $10 at lowes. Good investment. Might want to troubleshoot as much as you can before you call an HVAC tech out (They charge by the hour).

If they determine its an electrical problem, then you will have to pay them for showing up, then you may have to call an electrician, then reschedule HVAC tech to come back out. Ideally you want to determine the problem yourself, or at least narrow it down.

Mine (which does it all) is $39 at sears.

^ Good advice that.

Picked up a mulitimeter.

It shows no power in the wires.

When I test it on the tstat for our other zone, it shows hot wires.

You should have got 24v with RH and C.

Either wire is broke, disconnected at unit, or unit may be damaged. This assumes that unit has power as you stated previously, and it is just not getting to the tstat. Verify again all fuses, breakers, disconnects. Flip them on/off, remove and reinsert all disconnects (probably two inside, and one outside)

Now you have to find it, fix it, and/or pull a new wire.

If you have the money, and don’t want to mess with it, then call a HVAC tech. If your unit is damaged, be prepared for sticker shock (unless your unit is still under warranty). DO NOT tell them you messed with it or anything as that may void any warranty. Put the original tstat back on.

Stick with facts:

Tstat not functioning, and you suspect it is not receiving 24v. (remove tstat batteries so it is only on C common)

If you want to troubleshoot it further, open up the front of the unit, find the red wire (RH) that goes to tstat, disconnect it, and do a tone continuity test. If its good, then its at the unit I would guess

Use ohm

(disconnect another wire at unit, connect both ends of the red and whatever other wire you used at tstat, and meter both ends at unit. If you have continuity, wire is good. If you don’t, then wire is bad, you can try to attach another unused wire, or try to pull another wire through to tstat)

You can also test it by connecting the brown wire (Y2) to unit and tstat in lieu of red RH. Connect all wires like normal, leave red disconnected on both ends, and of course brown is now RH instead of Y2.

If you are lucky, its the wire (which you can get at lowes/home depot) for a few bucks.

If wiring is good, or still doesn’t work with brown as RH (meter brown and C common for 24vac), then you probably have a bigger and potentially more costly problem… damage or power issue at unit.