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My ac and heat wont turn on off. I bought a new thermostat, but when you turn the unit off the blower still is running and the unit outside (compressor) still runs. If you switch it to heat it does the same, just runs and runs. I was thinking it was one of the relays on the main unit itself in the box with the Heat/ AC and the Auto/continuous switches. Any thought before i spend any more money. Can i test the switches/relays with a multi meter? thanks for any help or direction you can give.

Kemp

Hi Kemp,

What is furnace model number ? Where are you turning it OFF at ?


In heat, is it just the blower or is it the blower and heat source ?



Thanks,
Robert

Trying to turn it off with the thermostat. With the switch on the unit under the panel it will turn off the blower. For the a/c we just used the circuit breaker to turn that off.It is both the blower and the heat source, as with the a/c both the a/c compressor and blower are running. Not sure of the model number, we are at a family members house right now. It is the Coleman Presidential III, sorry thats all I have right now.

Hi Kemp,

With electric heat, you'll have element plates at facing of furnace with either one or two element coild per plate.


On the plates will be the limit and wiring to each coil.

Would you know how many element coils you have ?


Or, do you know the KW (Kilo Watts) of your furnace ?


If not any of above, when you return home, any of those or the model number will allow me to quote a price on needed part.


Fairly certain I know what is wrong, but need correct one for your size furnace as to KW rating .



Thanks,
Robert

It is a gas heater. When I get home I will find the specs out

Hi Kemp,


Ok, let's start fresh since it's a gas furnace and not electric.


Get me model number first.


Set t-stat for heat and when it keeps going and not shutting down (burner and blower), test at gas valve for 24vac.




Thanks,
Robert

ok here are the numbers from on the unit:

A/C Blower # 7900/6821
Furnace # 7975-856

BTU/hr
Input= 75,000
Output= 60,000

Hi,

Did ya test the gas valve for 24vac.


Thanks,
Robert

Not sure what the gas valve is? do you have a diagram? and would that prevent the ac from shutting off?

Hi Kemp,


The gas valve is the component in furnace that controls gas flow to burner.


You stated the heat was on with blower also.


Trying to determine why, it may play a role in why a/c stays on.


Thanks,
Robert

I will get a multi meter tomarrow and see if I can find the gas valve and see if it is getting 24v. I will get back to ya. Thank you much for your time and help.

Kemp

Hi Kemp,


Go here and scroll down to gas valves:

http://www.mobilehomerepair.com/ColemanGas.html


Yours is 7956-336P . Click on pic for enlarged view.

Your current one will look a little different as this is the new style.


It will though let you see what to look for at midway or just below mid way of furnace.


With a call for heat, you'll have 24vac at GV. With no call for heat, there should not be a 24vac present at GV.


For burner to remain lit, GV has to be open. Need to know if problem is a bad GV or is there an electrical problem keeping 24vac present at GV.


Also, when in cooling mode and a/c outside and blower inside going continously, have you looked in furnace to see if the heat burner is also lit at that time?


Thanks,
Robert