Heat/AC/Fan not working at all. Resetting circuit breaker did not fix problem. Heat/AC is one unit. Unit has its own circuit breaker with two fuses. Replaced both fuses - did not fix problem. Replaced dial thermostat with new digital - still did not fix problem. Thermostat wiring is accurate. When thermostat is set for either Heat or AC, a "click" can be heard, but Heat/AC/Fan does not function. Heater has electronic ignition. Unit is 220volts. I used a pen-like AC-DC tester that has lights that indicate 110v, 220v, 277v, 460v. Tester functions properly. Tested wires going into Heat/AC Unit: Black, White, Ground. Tested Black to Ground: 110v OK. Tested White to Ground: 110v OK. Tested Black to White: PEN DID NOT LIGHT UP AT ALL. Am I testing correctly? I also have a Multi-tester but do not know how to use it. I will do research on Multi-testers... HISTORY OF HEATER/AC UNIT: Unit worked PERFECTLY FINE before I rented out my home for 1 1/2 yrs. When tenants moved out, the Unit went completely non responsive. I purchased my property in 2002 with this Heat/AC unit. Don't know how old Unit is. Should I continue to troubleshoot? Are Heat/AC Units usually covered under home warranty? Or should I call a Technician to come fix it? Any feedback will be appreciated. Thank you.

My best shot is a wiring problem at the panel where the unit gets its' 220V from. Someone is giving the machine the same phase, twice (using the black and white wires). They should be on two different phases in the disribution panel. There also may be a safety switch that has failed (high pressure, low oil, or something like that). Check the data plate for required voltage and number of phases. It could be 220V single phase, or 220V, 3 phase. In any case, the NEC color code as installed, is not correct for a 220V circuit. We used to call this kind of thing "Technician Tracks..." Please be careful when working around live voltages.

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Originally Posted by goldieshrimpie

Heat/AC/Fan not working at all. Resetting circuit breaker did not fix problem. Heat/AC is one unit. Unit has its own circuit breaker with two fuses. Replaced both fuses - did not fix problem. Replaced dial thermostat with new digital - still did not fix problem. Thermostat wiring is accurate. When thermostat is set for either Heat or AC, a "click" can be heard, but Heat/AC/Fan does not function. Heater has electronic ignition. Unit is 220volts. I used a pen-like AC-DC tester that has lights that indicate 110v, 220v, 277v, 460v. Tester functions properly. Tested wires going into Heat/AC Unit: Black, White, Ground. Tested Black to Ground: 110v OK. Tested White to Ground: 110v OK. Tested Black to White: PEN DID NOT LIGHT UP AT ALL. Am I testing correctly? I also have a Multi-tester but do not know how to use it. I will do research on Multi-testers... HISTORY OF HEATER/AC UNIT: Unit worked PERFECTLY FINE before I rented out my home for 1 1/2 yrs. When tenants moved out, the Unit went completely non responsive. I purchased my property in 2002 with this Heat/AC unit. Don't know how old Unit is. Should I continue to troubleshoot? Are Heat/AC Units usually covered under home warranty? Or should I call a Technician to come fix it? Any feedback will be appreciated. Thank you.

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Souns like there may be a t-sta problem or even a problem with the transformer.

If your system is a 115v system (gas furnace) you need to check for voltage from black to white going into the furnace. With a pen-like you get feed back readings through the windings of all electrical parts. You may have lost your common leg (white wire)and nothing will work. It needs to be checked with a volt meter to help solve the problem.

Thank you all for your input. But it's getting a bit too complicated for me... I'm going to call it quits and will be leaving it to the specialists. Sure hope I don't get ripped off... Anyone know of a reputable HVAC institution in the Cypress, CA or Buena Park, CA area? I pulled up several listings off Google, but which company is truly reputable?

Check your Chamber of Commerce or Better Business Bureau. Consider, if you interview two different technicians... one 45 years old, the other 20 years old. Both say "I've been a tech all of my life"... which do you trust more?