Gas and Oil Home Heating Furnaces - Fan NOT work on auto, pilot out when burner off
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emilypenelope
12-25-04, 12:40 AM
Have old (circa 1977) Carrier upright gas furnace with A/C.
Model #58GC???2-A, Series 222. It has a standing pilot light. At start of the season it didn't work at all. Have come a long way by reading your great site and send many thanks. 2 major problems. Furnace will run for hours, but when tstat calls for heat off and burner goes off, pilot light goes out too. I have to re-light pilot every time. Also, the blower does not work on Auto. I am able to run it manually "ON". When I started "fixing" the furnace, the fan worked fine. I have spent hours reading your threads and am learning much, but am still ignorant. Can you lead me to a website that shows pictures of the components you are talking about so I might properly identify the parts I need to check? When I bought the house, the owner's manual was missing and I have not been able to locate one.
I have a Fluke multimeter waiting to serve. I have changed tcouple, thermostat, and filter and cleaned pilot and everything else I could get to. I finally figured out that when you talk about 24V that you mean AC, NOT DC (correct?).
We have cancelled Christmas because of >2 feet of snow and ice here in Indiana. The wind chill factor is minus 20 degrees. The kerosene heaters are not good enough. I NEED HELP!
Please give me some ideas what to check to keep pilot burning when tstat calls furnace to go off, how to make fan work on Auto, and where to find general photos of furnace components. Thanks again!
Model #58GC???2-A, Series 222. It has a standing pilot light. At start of the season it didn't work at all. Have come a long way by reading your great site and send many thanks. 2 major problems. Furnace will run for hours, but when tstat calls for heat off and burner goes off, pilot light goes out too. I have to re-light pilot every time. Also, the blower does not work on Auto. I am able to run it manually "ON". When I started "fixing" the furnace, the fan worked fine. I have spent hours reading your threads and am learning much, but am still ignorant. Can you lead me to a website that shows pictures of the components you are talking about so I might properly identify the parts I need to check? When I bought the house, the owner's manual was missing and I have not been able to locate one.
I have a Fluke multimeter waiting to serve. I have changed tcouple, thermostat, and filter and cleaned pilot and everything else I could get to. I finally figured out that when you talk about 24V that you mean AC, NOT DC (correct?).
We have cancelled Christmas because of >2 feet of snow and ice here in Indiana. The wind chill factor is minus 20 degrees. The kerosene heaters are not good enough. I NEED HELP!
Please give me some ideas what to check to keep pilot burning when tstat calls furnace to go off, how to make fan work on Auto, and where to find general photos of furnace components. Thanks again!
coldmechanic
12-25-04, 10:07 AM
Well, ya got a couple of issues there. The pilot light going out could be that your Gas Valve has crud in it, or it's just plain going bad. The fan, however, concerns me more. Many units use a temp switch that not only turns the fan on when the furnace gets warm enough, but the same switch also turns the furnace off should it get too hot. Although I can't refer to a schematic, the wiring isn't that difficult and this needs to be fixed for your safety. If you have any trouble at all - get a service company to fix it.
Is your furnace LP or Natural Gas?
Is your furnace LP or Natural Gas?
danski0224
12-25-04, 10:23 AM
The pilot light creates voltage in the thermocouple. This voltage (very small) is used to operate a coil of wire in the gas valve. This coil of wire keeps the pilot light gas supply open with a magnetic field. No voltage means no power which means no gas.
Because the voltage and current numbers are so small, connections need to be clean and tight. Most standard meters cannot measure the current involved because it is measured in micoamps. There are special meters available that the end of the thermocouple assembly threads into.
The pilot flame needs to be aimed at the upper one third of the thermocouple. The voltage is created by heating two dissimiar metals, and their junction is at the tip. Your problem may be simply that the new thermocouple you installed is not positioned right, and the extra heat from the burners keeps it hot enough while the burners are on.
Does the pilot light stay on by itself? Have you tried to see if it stays lit for a few minutes before turning on the furnace right away? An audible click can be heard at the gas valve just before the pilot light goes out if the voltage is not good enough.
The "new" thermocouple can also be bad or marginal. Did you kink the "tubing" attached to the thermocouple?
The hold coils in the gas valve can also go bad. If that is the case, gas valve replacement is the only option. Due to liability issues, it will be difficult to find someone to sell you the part as a DIY'er.
There is no 24vac involved in the thermocouple and pilot light circuit. If the thermocouple is properly positioned (try a new one, too), the connections are clean and tight (no oil, pipe dope, etc) then you need a new gas valve.
As far as the fan goes, check for any loose connections, especially at the limit switch and that thermostat you replaced. If it worked before, you probably pulled something loose or miswired something. Double and triple check the thermostat directions, wiring and connections. Only two things control the automatic fan operation, the thermostat and the limit switch. There are other things involved at the control board level, but those are usually relays that do the switching, and your equipment likely predates a PC board. Carriers with a bad board usually have the fan on all the time.
Yet another possibility is a cracked heat exchanger. The burners turn on before the circulating fan, and are off before the fan is off. If the exchanger is cracked, drafts from the fan can blow out the pilot. Have you looked at the burner flame while the fan is on? Is the flame steady and mostly blue or does it jump around a lot with a bunch of yellow in the flame? Does the pilot go out immediately after the burners are extinguished (blown out) or does it go out after about a minute (thermocouple cooling due to improper placement)? A cracked heat exchanger allows carbon monoxide into the living space.
Do not sink too much money in your vintage equipment.
Remember that you are attemptimg repairs on a piece of equipment that uses gas and electricity, and has the ability to generate carbon monoxide. There must be a point when you step back if the going gets tough. Your life safety can be at risk. The few dollars saved are not worth it.
Because the voltage and current numbers are so small, connections need to be clean and tight. Most standard meters cannot measure the current involved because it is measured in micoamps. There are special meters available that the end of the thermocouple assembly threads into.
The pilot flame needs to be aimed at the upper one third of the thermocouple. The voltage is created by heating two dissimiar metals, and their junction is at the tip. Your problem may be simply that the new thermocouple you installed is not positioned right, and the extra heat from the burners keeps it hot enough while the burners are on.
Does the pilot light stay on by itself? Have you tried to see if it stays lit for a few minutes before turning on the furnace right away? An audible click can be heard at the gas valve just before the pilot light goes out if the voltage is not good enough.
The "new" thermocouple can also be bad or marginal. Did you kink the "tubing" attached to the thermocouple?
The hold coils in the gas valve can also go bad. If that is the case, gas valve replacement is the only option. Due to liability issues, it will be difficult to find someone to sell you the part as a DIY'er.
There is no 24vac involved in the thermocouple and pilot light circuit. If the thermocouple is properly positioned (try a new one, too), the connections are clean and tight (no oil, pipe dope, etc) then you need a new gas valve.
As far as the fan goes, check for any loose connections, especially at the limit switch and that thermostat you replaced. If it worked before, you probably pulled something loose or miswired something. Double and triple check the thermostat directions, wiring and connections. Only two things control the automatic fan operation, the thermostat and the limit switch. There are other things involved at the control board level, but those are usually relays that do the switching, and your equipment likely predates a PC board. Carriers with a bad board usually have the fan on all the time.
Yet another possibility is a cracked heat exchanger. The burners turn on before the circulating fan, and are off before the fan is off. If the exchanger is cracked, drafts from the fan can blow out the pilot. Have you looked at the burner flame while the fan is on? Is the flame steady and mostly blue or does it jump around a lot with a bunch of yellow in the flame? Does the pilot go out immediately after the burners are extinguished (blown out) or does it go out after about a minute (thermocouple cooling due to improper placement)? A cracked heat exchanger allows carbon monoxide into the living space.
Do not sink too much money in your vintage equipment.
Remember that you are attemptimg repairs on a piece of equipment that uses gas and electricity, and has the ability to generate carbon monoxide. There must be a point when you step back if the going gets tough. Your life safety can be at risk. The few dollars saved are not worth it.