I changed the thermostat from an old Honeywell to a programmable Honeywell 5-2. I have central air & heating is an electric water heater. I programmed it and thought all was well. I came in today and it was 86 degrees. The fan is working but not the air. I set air at 72 and the screen says cool on... but nothing is blowing. Then when I turn on the fan, it blows. I called up a heating & cooling company. They want to charge me $100 just for the call :( I told them what was going on, and they said it was probably the wiring. It had 4 wires red, yellow, green and white.. I put them in the appropriate places and screwed them in. If I did everything by the book, how could it be wiring? Is it possible the thermostat is not compatible? The customer service rep walked me through programming. She did say she didn't know if it was compatible and later said it was. But, I'm not so sure. This was my first & last attempt as a girl DIY. I'm now scared to death it's something big.

The thermostats is just a simple switch. Any should work if wired right. It switches the red which you can think of as hot, to the white, yellow, or green for heat, A/C, or fan only. If both thermostats had terminals marked R, W, Y, and G, and you just moved the wires to the same terminals, it should work. Remove the thermostat, and touch the red and yellow wires together. Note, a wire can break and be held together by the insulation. See if the yellow wire is too flexible somewhere. If the outside A/C compressor doesn't start up in a few minutes, follow the yellow out to it. It may go to the blower, and then a pair of wires out to the compressor. The outside unit has both a fan, and a compressor. In addition to the fan, you should be able to hear a put, put, put.

Let me know what you find. Also, if you don't find a misplaced wire, let me know if you have exotic tools such as a voltmeter.

The old one looked like a dinosaur. On the back, it had R, G, Y, W wrapped around and screwed in. I had to snip the ends of the wire to get them off the old thermostat. There was a blue wire that was cut short and wrapped away from the other wires. The old thermo has mercury on the back (not sure if that's relevant) Honeywell told me just to dispose of it correctly. The electric water heater is 240V. When the rep first asked she said she didn't think the water heater was compatible with the thermo. She then said she thought it was OK.


I'm away from the unit so I can't try that. But, I will give it a try tomorrow morning. I appreciate your help, I'm pretty desperate.

Edited to add: the manual says check circuit breaker and reset if necessary, make sure power switch for heating & cooling is on, make sure furnace door is closed, wait 5 min for the system to respond. It also says if it flashes "cool on" compressor protection feature is engaged. Wait 5 minutes for the system to restart without damage to the compressor. It does flash cool on when the air should work. None of this is English to me.

Don't bother talking to that lady again. She doesn't have a clue. The voltage of the heater makes no difference to the thermostat. It is powered by a 24 volt transformer connected to the red and blue wires. When any thermostat calls for cooling, it switches the R terminal to the Y one. Power then flows to a couple of relays or contactors. One controls the fan that circulates air inside the house. The other is outside and controls the compressor and fan outside. If either fan runs, the transformer, the thermostat, and the relay are working. Since the inside fan works, start checking the outside unit. If for that fan is running out there, and the small pipe going inside the house isn't hot, Call the guy that was $100 to come out. It will be more than that. If it isn't doing anything, check the circuit breaker at you main breaker box. It should be one near the top with sort of 2 linked together. Sometimes when they trip, they still look OK. Turn it clear off, and back on. Go outside and look for a small box connected to the wires to the A/C unit. Usually the handle pulls down. Open it up and see if it has fuses. Check them. Bad ones can look good. Replace them if bad. Close the box, and raise the handle to the on position. You may need to remove a cover from the A/C unit. Check to see if you have 24 volts at the small wires. If not, trace them back to the transformer and find out where the voltage disappears. If it does, give the relay, the sort of black plastic thingy with all the wires a rap with a screw driver handle or something.

If you are to be fixing things yourself, you do need to have a few tools. You should be able to go to a hardware or home center and pick up a basic multimeter and a voltage detector both for less than $25. I don't know how I lived for almost 60 years without a voltage detector. There are several brands. I have a GB Instruments GVD-505A, less than $15 at Home Depot. Touch it to a hot wire, and the end glows red. Find the doodad that lights it on one side, and not the other, and you have the culprit. Great for checking fuses.