Last night going to bed, all equipment was working. This morning I noticed it was a bit cool downstairs (I have a two zone house). The main unit which services the main floor and basement isn't running. Upon checking, I've noticed there is no display, aka no power to the Honey Chromtherm IV Plus thermostat. I checked the breakers on the air handler unit in the basement, checked the breakers in the circuit panel and then went outside to ensure the switch there wasn't off. In all cases, while they were not tripped, I have turned off and back on these breakers. Still no power.

I understand there should be 24V to the thermostat, but will I need to remove the screws where the wiring is connected in order to get a good reading? Without unscrewing, I could not get 24V anywhere.

BTW, the outside electrical box has no fuses or throw switch. Mine have a switch block that you remove, flip over, and then reinsert to put in the off position.

How can I check voltage at the air handler, or better question, from which piece of equipment does the thermostat receive its power? Are there any other scenarios that could prevent power fom getting to the thermostat besides the actual wiring from equipment to thermostat?

The heat pump is a Luxaire 4ton SEER 10 approximately going on 4 years old. Filters are changed regularly.

Thanks.

Andy

Check the transformer in the inside air handler for 24 volt output.

Last night going to bed, all equipment was working. This morning I noticed it was a bit cool downstairs (I have a two zone house). The main unit which services the main floor and basement isn't running. Upon checking, I've noticed there is no display, aka no power to the Honey Chromtherm IV Plus thermostat. I checked the breakers on the air handler unit in the basement, checked the breakers in the circuit panel and then went outside to ensure the switch there wasn't off. In all cases, while they were not tripped, I have turned off and back on these breakers. Still no power.

I understand there should be 24V to the thermostat, but will I need to remove the screws where the wiring is connected in order to get a good reading? Without unscrewing, I could not get 24V anywhere.

BTW, the outside electrical box has no fuses or throw switch. Mine have a switch block that you remove, flip over, and then reinsert to put in the off position.

How can I check voltage at the air handler, or better question, from which piece of equipment does the thermostat receive its power? Are there any other scenarios that could prevent power fom getting to the thermostat besides the actual wiring from equipment to thermostat?

The heat pump is a Luxaire 4ton SEER 10 approximately going on 4 years old. Filters are changed regularly.

Thanks.

Andy
Have checked the transformer and was getting 27.2V. The transformer feeds some type of circuit board. While looking it over, I noticed a 5A fusible link that had blown. Shutting off all power, I replaced the fusible link. Then turned all power on again. The link blew again in about 10 minutes.

1. What could cause this fusible link to blow so quickly?

2. Is 27.2V a nominal measurement for the transformer, or does this transformer need to be replaced so that a true 24VAC is generated?

Andy

I think it took ten minutes because although I turned the system on, due to room temperature, the thermostat didn't signal a need for heat for about ten minutes after I reset the time of day on the thermostat. I'll start looking for shorted wires. I read in other answers that a relay could cause this scenario also? If that's the case, where would I find that relay, and how would one go about checking it?

Thanks again.

Andy

Transformer OK at that voltage. You will have to find the short circuit in order to stop the fuse from blowing. I would start looking for wires that have rubbed the cabinet. The thermostat wires etc. I am surprised it took 10 minurtes. Usually they blow right away.

Meant to reply earlier. Short found at the heat pump high pressure limit switch wiring where it was rubbing the copper pipe from the condenser.

Check the fuse on the circuit board inside the furnace should be a 5 amp fuse. Try these, Disconnect your red wire on R and Green and your white see if the heater kicks on. Wirenut those 3 wires together that u just removed from your thermostat area. Unit should kick on. Check thermostat for batteries also. Try these. If the unit kicks on u have a bad thermostat. If not, check power going into the furnace and check if your transformer is putting out 24 volts to low voltage wires.

Now that you have found the short all should be OK. BTW make sure you replaced the fuse with exactly the same value. Good Deal. Merry Christmas.