FURNACE AND AIR RUN AT SAME TIME

gas furnace??? check the start capacitor, put unit in ac mode and see if fan comes on(switch fan to on at thermostat) if it does not a fan problem or capacitor problem. when in cooling mode thermostat controls fan, when in heating mode, furnace controls fan

Try setting the temperature higher. It could be that the room temperature is not getting cold enough for the automatic controls to activate the heater.

Wish I knew how old your furnace is. Let me answer your question directly. In the heat mode the fan runs independently from the air conditioning fan relay. Its either brought on by time or temperature. An old furnace will use a fan and limit control that uses a coil to sense the heat exchanger temperature and turn the fan on or off. Newer furnaces use a timer on a circuit board. 20 years or newer Ill bet its a timer board. Follow the blower motor wires back to the component and ill bet that's the culprit. Hope it helps. Good luck.

Change thermostat.

Go to your thermostat and access the fan mode. Change the fan mode to Automatic, AU. This will stop the AC fan from blowing when the furnace is turned on. If the fan mode is on Hi or Lo and the furnace is turned on it will turn on the AC blower. Bad design...

Go to the thermostat and access the fan mode. Change the mode to AU (automatic) then turn the furnace on and it should work normally. If the fan mode is in Hi or Lo the Ac fan will blow.

Depending on the model of the furnace, the blower is either a 2 or 3 speed. When the furnace operates in heating mode with the thermostat in the auto position, the furnace starts the fan when the furnace reaches a specific temperature or after a set time delay, but it operates the fan in low or med low speed on heat mode, when you put the thermostat fan switch in the "ON" position, the furnace operates the fan in "HI" speed, the same speed used for cooling mode. You may have a blower moter that is starting to short. I would recommend having a professional replace the motor before now before it becomes an emergency in the middle of the night during a cold spell.

on some carriers they have a lock out feature outside to reset shut down power to furnace for 90secs. and then restart

Peace,




It seems you need hands on servicethis time !
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This should be doable: First get pen and paper-start at the furnace, theres a group of 5-8 wires leaving the furnace anfd going to the thermostat and a group of 2-3 going to the condenser outside that all need to be identified and the location in the furnace recorded if your furnace has a control board simply right the letter and the corresponding wire color:and whether it belongs to the condenser grp or the T-stat grp.

Furnace
R-red-to t-stat
C-yellow to cond
Y-red to cond and yellow to t-stat
G- green-to t-stat
W- white- to t-stat

If you dont have a circuit board youll be doing the same thing but using the components rather than letters;

Transformer 24v- red to t-stat
transformer 24v com -yellow to cond
Red from cond connected to yellow from t-stat
fan relay - green to t-stat
gas valve - white to t-stat

K then go to you t-stat and simply connect the corasponding component or leter to the thermostat gterminal

Cond Furnace Thermostat

yellow com- blue -C or B
gas valve or w-white -W
fan relay or g -green -G
trans 24v or R -red - R
red connection to cond or Y on board -Y
Hope this helps.