Gas and Oil Home Heating Furnaces - AIR/HEAT SYSTEM GONE MAD!
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04-21-01, 11:48 AM
I HAVE A SPLIT SYSTEM GAS FURNACE/ ELECTRIC COOL. I TURNED THE HEAT OFF FOR THE SEASON THE OTHER DAY. A COUPLE DAYS LATER, IT GOT COOL SO I TURNED IT BACK ON. WITH THE THERMOSTAT SET ON HEAT, I NOTICED THE CONDENSING UNIT IS NOW RUNNING AND THE AIR IS NOT WARM. WHAT GIVES?
CoolBreeze
04-21-01, 12:46 PM
Hi,
Your Heat System consists of Fan/Blower in Furnace to circulate the air and your heating coils to warm the air.Your A/c consists of same Fan/Blower to circulate air,Evaporator Coil above Blower to cool the air/absorb the warm/hot air from home and the compressor/condensing coil/outdoor fan in outside unit.OK,during winter you ran Furnace/Blower/Heating Coils,then when it got warm weather,you switched to A/C and ran Furnace Blower/Evap. Coil/Comp.-Condensing Coil/Outdoor Fan.Sounds like when you switched back to Heat,your contactor(Electrical control for outside condenser) stuck in closed position keeping A/C System going(Reason for condensing unit running) and then when you switched to Heat, your Heating System came on and now both units are running at same time.The heat supposed to warm your home is flowing over Evap. Coil and being cooled by A/C System which is also running being controlled by stuck Contactor.The contactor has a magnetic coil that is energized by 24 volts sent from t-stat, which closes contacts sending 240 volts to comp./outdoor fan.When you switch t-stat to heat,it stops the 24 volts to contactor and opens contactor contacts turning off condensing unit.240 volts is always present at one side of contactor awaiting 24 volts to close contactor.When you switched t-stat to heat,the 24 volts de-energized coil but, the contacts probably were pitted/burnt and stuck closed keeping 240 volts flowing across contactor and keeping A/C running.Then you turn on heat at t-stat and it comes on,pulling cool/cold air from home across heating coils warming the air as normal,but the air then flows across Evap. Coil which is running too now and it cools the warm air just as it does during normal A/C mode(reason for cool air).You can turn off breaker/fuse to turn off ALL power to t-stat and unit,take cover off t-stat to reveal wiring and disconnect (Y)-Yellow wire,put elect. tape over end of it,replace cover,turn on breaker/fuse/power and set t-stat to heat/auto and if outside unit comes on,the contactor is stuck.Check also to see if Furnace Blower/Heating Coils and Outdoor Fan/Comp. are running at same time with Y from t-stat disconnected and t-stat on heat/auto.Hope this helps,write back with what you find after checking this and we'll give more details/info as needed.Take Care.
CoolBreeze
[Edited by CoolBreeze on 04-21-01 at 02:51]
Your Heat System consists of Fan/Blower in Furnace to circulate the air and your heating coils to warm the air.Your A/c consists of same Fan/Blower to circulate air,Evaporator Coil above Blower to cool the air/absorb the warm/hot air from home and the compressor/condensing coil/outdoor fan in outside unit.OK,during winter you ran Furnace/Blower/Heating Coils,then when it got warm weather,you switched to A/C and ran Furnace Blower/Evap. Coil/Comp.-Condensing Coil/Outdoor Fan.Sounds like when you switched back to Heat,your contactor(Electrical control for outside condenser) stuck in closed position keeping A/C System going(Reason for condensing unit running) and then when you switched to Heat, your Heating System came on and now both units are running at same time.The heat supposed to warm your home is flowing over Evap. Coil and being cooled by A/C System which is also running being controlled by stuck Contactor.The contactor has a magnetic coil that is energized by 24 volts sent from t-stat, which closes contacts sending 240 volts to comp./outdoor fan.When you switch t-stat to heat,it stops the 24 volts to contactor and opens contactor contacts turning off condensing unit.240 volts is always present at one side of contactor awaiting 24 volts to close contactor.When you switched t-stat to heat,the 24 volts de-energized coil but, the contacts probably were pitted/burnt and stuck closed keeping 240 volts flowing across contactor and keeping A/C running.Then you turn on heat at t-stat and it comes on,pulling cool/cold air from home across heating coils warming the air as normal,but the air then flows across Evap. Coil which is running too now and it cools the warm air just as it does during normal A/C mode(reason for cool air).You can turn off breaker/fuse to turn off ALL power to t-stat and unit,take cover off t-stat to reveal wiring and disconnect (Y)-Yellow wire,put elect. tape over end of it,replace cover,turn on breaker/fuse/power and set t-stat to heat/auto and if outside unit comes on,the contactor is stuck.Check also to see if Furnace Blower/Heating Coils and Outdoor Fan/Comp. are running at same time with Y from t-stat disconnected and t-stat on heat/auto.Hope this helps,write back with what you find after checking this and we'll give more details/info as needed.Take Care.
CoolBreeze
[Edited by CoolBreeze on 04-21-01 at 02:51]
PDF
04-21-01, 03:29 PM
Make sure you do not have a heat pump with second stage gas heat.PDF
fjrachel
04-21-01, 03:57 PM
Shut off electric to furnace, if condenser is still running, you have a fused contactor. If condenser shuts off, you have a control problem. Then you'll need an ohm/volt meter and know how to use it to check wiring. Problem may just be the t'stat...