A/C nor Heater will turn on.

Here is what to do . Pull out or turn off Electrical disconnect behind unit . Carefully remove panel covering controls in unit . Note most units have a flat panel with a few screws, but some GE units have a welded metal box on top of unit which needs to be removed. After exposing controls. replace or turn on disconnect. Then take a plastic handled screwdriver and push in on center of contactor (boxlike part with a lot of wires hooked ) If the compressor now comes on release contactor , and check for 24 Volts AC at base of contactor where thermostat (small wires that run on outside of black refrigerant line ) with thermostat on and calling for cool you should measure 24 to 28 volts . If voltage is present replace contactor after disconnecting from power. If no voltage go inside , remove cover from thermostat, and check for 24 volts between red ( R) and yellow (Y ) terminals on thermostat , If voltage is present , replace thermostat , no voltage check voltage in heater / air handler if you have voltage at air handler , replace thermostat wire from heater to thermostat / if no voltage check for blown fuse in heater , this should be either an inline fuse or an automotive type fuse plugged into circuit board (with power to heater disconnected check broken wire or black mark in fuse when held up to light. If fuse good turn on power to heater and check for 230v to one side of transformer, if you get voltage to Primary (incoming side ) of transformer, check output side of transformer for 24 - 28 volts. If transformer shows input but no output replace transformer after turning power off. If you heard a buzzing or grinding noise , when pushing in contactor , but compressor didn't start look at run capacitor (this is round or oval shaped object with wires going to contactor and compressor ) Looking at area where wires plug this should be a flat surface , if it looks domed shaped or bulging out , it is blown and needs replaced , use same mfd rating and 440 Volts to be on safe side. / If there was no noise from compressor when contactor was pushed in , put your hand on top of compressor (black object in center of unit ) If hot , allow to cool for at least three hours with power to unit turned off and retest . If compressor comes on after cooling , check for bad fan motor in outside unit (it may make a squealing or wining noise and stop runing for a while , also check for / clean outdoor coils
Hope this helps .
Thanks,
Alex

by heater i take it you mean the blower motor.these work on a fuse and or relay and a set of resistors.but start by checking the fuse as you said you have no poower.if the fuse is ok then check for power at the plug on the blower motor, you will have to disconnect the plug at the blower motor and have a tester placed on 12 volts to perform this test.turn ignition to the on position and turn on the heater unit,you should have a reading of some kind .if you have up to 12 volts then the wiring and fuseare ok. the problem then would be the blower motorbut after removal you could always check the motor by hooking it up to a 12 volt power source to see if it turns.

If the gas valve is getting 24 volts and still not responding then replace it. If it is not getting 24 volts then replace the circuit board.

check primary of thransformer AC mains volts, then
check secondary of transformer AC low volts into each rectifier then check DC volts at capacitors then check DC volts at regulators inputs then check Dc volts at outputs
as you go draw cct diag and layout so you know where everything is and how it is connected.

if its the psu you will find the fault, only ever replace items with original parts or direct equivalents.


Hope this helps
Thanks for using FixYa

Hi, what you need to do is determine if you have 24 volts to the thermostat. If you do not have a voltage meter, put stat back together and turn the fan to the on/manual position to see if it comes on. If it does, but the a/c does not work in the auto position, you need a new thermostat. If the fan runs, it shows us it has 24 volts to it. If you don't have an electrical meter, you can get a cheap one at Sears tools, or OSH for about $12 to$20 $$. Set it to a/c volts above 24 volts and touch one lead to the R terminal and the other to any of the other and you should get a reading of 24 volts. If not, you have lost power to the stat from the furnace. But, if the fan does run, you will not have to take these steps, just replace the stat as the circuitry has failed. So, I am not sure what type of heater and a/c you have. If it is a split system with the condenser on the outside of the house and heater inside, you will need to go to the heater section. Depending on the age of the unit, remove the panels to the heater. Just remember, don't go through all of these steps if the fan comes on. Look for a circuit board if the unit is 15 years old or newer. On this board you should see a S type fuse plugged in to it, a 3 to 5 amp fuse. Blue or amber in color. It is just like a fuse in your car. See if it is blown. It will be blackened, the metal S on top will be broken. Turn power off by unplugging the furnace and pull out the fuse.Look it over good. If you are not sure, replace it. Some of these panel doors have a power kill switch on the perimeter of the opening, that shuts the power off when you remove them. Make sure to put the panels on correctly for it to work when you are done. Your heater may have a view hole you can see through to see if it is on. You should see a red led light on. Oh, be sure you plugged it back in first. If the fuse was blown, this will solve your problem. If not, you will either have a problem with the 24 volt transformer or the circuit board. Before we go into that, do the checks I asked of you and let me know. I will wait to hear from you. Tell me about what kind of system you have also. Best of luck to you. Get back to me,
Sincerely,
Shastalaker7

What kind voltage is the heater operating on, 24 volt or 750 millivolt? If it is 24 volt check the transformer & thermostat for 24 volts along with gas valve, if it is a 750 millivolt system check the 2 wires coming from the pilot burner area for 750 millivolts, if you have a wall mount thermostat, tie the two wires together and see if main burners ignite, if they do replace thermostat. I really need more info to help you more, this unit came with two types of gas valves, a 24 volt & a 750millivolt type check name plate on unit to see which one you have.

Check for a fuse either in-line or on the circuit board. There should be 24 volts going to the thermostat. If not, you have either a bad transformer or a bad thermostat wire. Jump out the terminals that the thermostat wires are connected to. This should force the unit to fire. If not, bad circuit board.

check for 24 volts after transformer.does fan come on?does ignitor glow?

Please exercise due caution in checking voltages in live circuits!

24 volts sourced by the transformer, through the thermostat, then through the contactor (turns on power to compressor/fan) and returns to the transformer, If the thermostat is closed (calling for cool) you will see no voltage across it, but instead the contactor should be energized. Please note, 200 volts seems odd, you should have between 215 and 235. It sounds more like the contactor relay coil may be open. Is the contactor/transformer one piece?

Blank screen sounds like a fried thermosat. Abrupt outages can affect certain types of thermostats. Make a jumper wire and jump across R and G. See if you get any action from anywhere. If a fan or compressor kicks in you know you have a burned out thermosat...