So I installed a programmable thermostat in my house back in november. Worked beautifully on heat mode. Just tried to kick it over to cool today and it never turned on the AC unit. This is a gas furnace with an AC unit outside. I can get more detailed specs on the units if it will help.
It was wired up for 5 wire installation, then I looked at the furnace itself and thought it might actually be 4 wire. Before I really mess anything up, I wanted to see if anyone would know what I did wrong. First picture is of the thermostat side, second picture is of the heater.
all looks well with the wiring. I know it sounds stupid but did you check your 220 v.a.c circut breaker for the outside condensing unit?
also there should be a disconect box outside near the condensing unit as required by code, check to make sure it is in the on position. you most likely will have to open up the front cover to see the actual disconect.
another question. Is your furnace blower fan coming on and running when you switch it to cool and drop your set temp. below room temp. ?
Like was said above, check the outside disconnect box as well as the double pull breaker you have downstairs in your electrical box.
If you are able, check to see that you have 24V coming across the cooling wire on the thermostat.
I work for a local HVAC company, if you need a service call for someone to stop out and take a look at it, let me know, I’ll get you a discounted rate and try and get someone out there ASAP.
EDIT - which wire is supposed to be 24V hot for a.c? If it is the Green wire, i think that you have it wired wrong and have it one wire off on the 2nd picture. I’m not 100% sure, but let me know which wire is supposed to be 24V hot for A.C.
based on above pictures it appears from what i can make out the wiring looks good.
It appears that a 5 wire cable was pulled from the t-stat to the furnace and that you used the blue wire as the common correct?
It also appears that you used standard 2 wire cable going to the condenser with wires red & white correct?
1 of the 2 wires going to the condenser needs too be wired onto terminal Y and the other going to common, along with what should be the yellow wire coming from t-stat terminal Y to furnace terminal Y.
If you have a volt meter , and with the thermostat on cool and set below ambient room temp. check for voltage between terminals Y and C on the furnace circuit board. Most furnaces have a door switch where the circuit board is located so make sure the switch is closed if its not nothing will work!
If you have 24 volt at the Y and C terminals at furnace then the furnace blower motor should start and run regardless of what go’s on outside that way you know all is well on the furnace end.
next would be to check voltage between what looks like the red and white wire’s outside in the condenser service panel. Take out disconnect to avoid a possible shock hazard if you are not familiar with the components within.
If you have the 24 volt at the condenser between your 2 low voltage control wires, your contactor should be pulling in. This is the main switching component that closes with 24 volt power applied
this device will have the main 220 v.a.c leads wired into the bottom side of it. With the top leads going to capacitor , fan motor, and compressor.
If the contactor is pulling in “closing” and you have 220 v.a.c power to the contactor, then chances are you have a bad capacitor.
Depending on unit it is usually a split run style capacitor for both the fan motor and the compressor.
If you change the capacitor out for test , both the fan motor and compressor should start. if only one or the other starts then which ever didnt is bad
The only time that the freeon charge would be an issue on it not runnin would be in a very high end condensing unit that would have a low pressure switch.
If pressure within system drops too far it would open the switch not allowing the control circuit to be completed. wich prevents the unit from running
A vast majority of new units (within the past 3 years or so) have both high and low limits on them, especially those with Scroll compressors that they are concerned will burn up even on a very small change in freon level.
well, I’m not sure if it’s all up to code, but my wife noticed that the t-stat that I had installed said in the instructions “not for use with heat pumps or multi-stage systems”. I’m not really sure what that meant, but I went out and bought a new t-stat that supported both of those things.
as steelcityevo said, the blue wire at the t-stat was run to common on the furnace circuit board. I decided to hook that up to the C terminal on the new t-stat as the old one only had Rh and Rc to choose from. Everything is now working, as I tested the heat and cool this time, instead of only testing heat like I did last time :banghead:
Does this make sense to any of the experts? It’s been working as planned for about 6 hours now and we haven’t blown up, so I think I actually figured it out. Thanks for all the help everyone! The advice and offers for help were much appriciated
i highly doubt you have a multi stage AC or heat pump at your place, so that probably didn’t have anything to do with it.
On the old t-stat, was there a jumper between the Rh and the Rc? If not, I’ll bet that was the problem that you were having. It was energizing in heat, but not in cool mode.
there was no jumper in there, and I was going to put one in, but the directions said not to with a 5 wire set up. I should have tried it and saved myself $40 but it’s over with now.
