heil furnace/ac unit will not come on

[newnew]

my furnace and ac unit will not come on.it seem there is no power going to unit.i reset circuit breaker and change thermostat...........help (smile).heil model #hugb105ag01

[HayZee518]

Is there an emergency cut-off switch that's off? If it's an oil burner check the thermal cut-off switch which is mounted on the ceiling above the unit.

[LazyPup]

On central HVAC systems the inside unit (Evaporator section) has a separate power supply from the outside (condensing unit).

Switch the Thermostat to AC and set the temperature control very low.
check both the inside and outside unit to see if either come on.

If one but not the other comes on you know there is power to the Thermostate control section.

Double check your breakers,,often people are only aware of the breaker marked AC. The Breaker marked AC is only for the outside condensing unit.

There is another breaker for the inside unit.

If Your inside unit has an electric heater in it (Electric heat or Heat Pump with backup strip heat) the inside breaker will be a two pole 220v breaker.

If you have gas or propane heat the inside unit will probably have a single pole 125v breaker. (fan motor only)

Check the covers on the furnace unit, some furnaces, especially gas furnaces have a safety interlock button on the access panel frame. If the panel is loose or off, the interlock disconnects the power to the control section.

As Hazee pointed out, oil fired furnaces and some gas furnaces have a safety cutout switch that is normally mounted in the overhead space near the furnace.

In some localities, when the furnace is in a basement the safety cutout may be mounted on a wall on the main floor of the living space. Normally it will look like an ordinary light switch but it will have a red cover plate over the box and the cover may have the words "oil Burner" printed on the cover. If you have that switch, make sure it is turned on.

If you have a volt meter and are familiar with electrical troubleshooting locate the control transformer.

Disconnect one wire from the transformer secondary side and measure the transformer output voltage (should be between 18vac and 24vac).

If you have zero voltage check the primary side of the transformer (black and white wires- should be 125 volts)

If the primary voltage is zero, the problem is in the power circuit to the inside unit.

If the primary voltage is 125vac and the secondary is zero- replace the control transformer.

If you have the proper control voltage and both the inside and outside units will not operate the problem is most likely in the thermostate or thermostate control wiring.

Double check the wiring on the thermostate base plate. Also, carefully check the wiring instructions for the new thermostat. Some thermostates require changing a jumper wire inside to convert from gas to electric systems or to include both heat and AC.

[imeduc]

and change thermostat
Have to ask Why?? Jump R to G and see if the fan comes on inside .If so transformer is ok If not Id put a new transformer in. It would pay you to get a small test meter to use when you have this kind of trouble Ill bet it would have paid for that new tstat

ED

My mistakes dont define me they inform me.