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Tim H.
Tim H., HVAC Professional
Category: HVAC
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Thermostat is showing lower temperature (54 degrees) than set

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Thermostat is showing lower temperature (54 degrees) than set temperature (72 degrees). Cold air is coming through registers

Tim H :

Thanks for giving me the opportunity to help! Make and model number of furnace? Are you getting a LED diagnostic code?

JACUSTOMER-uuy7ui89- :

No. Display just shows HLD 53 degrees, even though I tried to set it at HLD 71. Arrow is also pointing to SYSTEM ON.

Tim H :

Make and model number of furnace? Are you getting a LED diagnostic code?

JACUSTOMER-uuy7ui89- :

Frigidaire heating & cooling unit. Model C38A 036A. I don't think the thermostat has an LED diagnostic code.

Tim H :

The LED code would be on the furnace, most likely on a lower door and inside a small window.

JACUSTOMER-uuy7ui89- :

I will check for it now. Be back shortly.

Tim H :

OK

JACUSTOMER-uuy7ui89- :

Theres

JACUSTOMER-uuy7ui89- :

There's a sticker above the condenser pump with the following: FG6RA 072C 12 A. I also took the door off the furnace. The door has a status red light column. The red light in the furnace is flashing once periodically, which lists limit circuit open or external load on W as the fault condition. There are also operating instructions to turn off the gas to the appliance. This unit does not have a pilot.

Tim H :

????

Tim H :

Do you have blower if you turn thermostat to fan "on" position?

JACUSTOMER-uuy7ui89- :

Yes, and now it is blowing cold air.

Tim H :

You most likely have an open limit switch, then

JACUSTOMER-uuy7ui89- :

What does that mean?

Tim H :

It means one of the limits, either the main or flame rollout switch is open.

Tim H :

I can't bring up anything with that model number you gave me.

JACUSTOMER-uuy7ui89- :

I have the wiring diagram for the furnace. It says it's for 78+ 80+, 90+ & 93+ model furnaces. Does that help? Should I try turning the furnace off and then on again?

Tim H :

Flame rollout switch should look like this

JACUSTOMER-uuy7ui89- :

I will see if I can find this switch on my furnace. Should I try to close it?

Tim H :

Yes, it has a reset button

Tim H :

The high limit, if it's open is not resettable. It should reset by itself, otherwise replace.

JACUSTOMER-uuy7ui89- :

OK. I will try to find it. Also, I did see a narrow red lever outside the furnace. It kind of looks like a pilot light.

Tim H :

OK

JACUSTOMER-uuy7ui89- :

I will be right back.

Tim H :

OK

JACUSTOMER-uuy7ui89- :

I didn't find the flame rollout switch, but I found the model number: FGRA 072C 12A. I also found what looks like a black arrow on a circle that was pointing to ON. I can switch it down to OFF. Don't know if that does anything.

Tim H :

I don't know what that would be... We are talking about a Frigidaire forced air furnace, right?

JACUSTOMER-uuy7ui89- :

Yes

Tim H :

There should be a high limit switch right above the burners.

Tim H :

How old is this furnace?

JACUSTOMER-uuy7ui89- :

I think it's about 8-10 years old. Also the operating instructions on the door say that the unit does not have a pilot, but it has an ignition device which automatically lights the burner.

JACUSTOMER-uuy7ui89- :

Sorry, hit the reply key too soon

Tim H :

Here are some high limit controls. Any look like yours?

Tim H :

May also look like this.

JACUSTOMER-uuy7ui89- :

The operating instructions also say that the black knob is the gas control knob. It says to turn it off for five minutes, then on. I am going to try that and also look for the high limit controls. Be back shortly...hopefully!

Tim H :

OK. This may take a while so I'll switch to Q and A mode. You can still post questions.

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