Troubleshooting Furnaces, Heat Pumps and Air Conditioners

Troubleshooting a furnace or air conditioner whether it be fired by gas, electricity or oil requires special tools, testing equipment and a host of other items. Since most people who are mechanically inclined may have some of this equipment there is the danger that they will think they can handle the job. To these people let us say up front, the author of this article is a Certified General Motors mechanic, but just as the automotive industry has added such things as air bags, computers, fuel injection, turbo chargers, superchargers and many other new components, so have the H.V.A.C. manufacturers. While you may have some of the equipment to test a vehicle, chances are you will only get just so far in troubleshooting the newer components.

Then there is the chance of getting hurt as in the case of working on an air bag system not to mention damaging expensive parts from the lack of having the right testing equipment. New furnaces and air conditioners have the same issues. As an example, the newest type of refrigerant out in some air conditioners use R-410A refrigerant which has the possibility of running operating pressures into the 700 pound range. A brand new set of refrigerant gauges and hoses which are meant for the old refrigerants are only rated for about 650 pounds!

All H.V.A.C. technicians have to buy new gauges and matching hoses not to mention new refrigerant recovery equipment as required by the E.P.A. If they don’t, someone is going to get hurt for sure! We are writing this article only as a guide and strongly suggest that you call a reputable H.V.A.C. service professional to service your gas, electric or oil furnace and your gas, or electric heat pump or air conditioner. So with all that said we will attempt to write this page with the emphasis on simple troubleshooting aimed at the average homeowner. If you are more mechanically inclined than this, please bear with us as we will include more technical advise noted as ” For Advanced Troubleshooting “.


DESCRIPTION: Oil, natural gas, L.P. gas fired and electric strip heat.

Most older gas furnaces usually have a pilot which burns all the time. This pilot burns and its flame must touch a sensing device called a thermocouple. The thermocouple generates a small amount of electricity within itself.

Note: ” For Advanced Troubleshooting”

There are millivolt systems which use pilot generators, that are totally different than the thermocouples used in standard 24 volt furnaces. The thermocouple can fail thus providing a safety against the furnace trying to send raw gas to the burners with no pilot present. If your pilot won’t stay lit even though you have followed the pilot lighting instructions usually posted within the furnace burner compartment continue reading here.

These instructions vary from furnace to furnace but usually amount to turning the gas valve knob to the pilot position, holding down on the gas valve knob ( sometimes a separate knob ) while lighting the pilot with a long match and then continuing holding down for (2) minutes. After this 2 minute hold down period release the knob. The pilot should remain lit. If it stays lit, turn the knob to the ” ON ” position. The burners should light if the power is on and the thermostat is calling for heat. If the pilot goes out immediately after you have held the knob down for (2) minutes you probably have a bad thermocouple. This is the number one call we get on these old furnaces. There are also various electronic pilots used, especially in older furnaces such as the following, Bryant LH33WZ512A Spark Ignitor, Carrier Pilot Burner. Be aware however, a bad gas valve or open high temperature limit control can sometimes cause similar reactions.

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