Troubleshooting Furnaces, Heat Pumps, and Air Conditioners

Troubleshooting a furnace or air conditioner, whether it’s running on gas, electricity, or oil, requires special tools, testing equipment, and a number of other items. Since most people who are mechanically inclined may have some of this equipment, there is a danger that they will believe they can get the job done. For these people, let’s say from the beginning, the author of this article is a General Motors certified mechanic, but just as the auto industry has added things like airbags, computers, fuel injection, turbochargers, superchargers and many other new components. , so have HVAC manufacturers. While you may have some of the equipment to test a vehicle, you will likely only go so far in troubleshooting newer components.

Then there is the possibility of injury, as in the case of working on an airbag system, not to mention expensive parts damage from not having the proper testing equipment. New furnaces and air conditioners have the same problems. As an example, the newer type of refrigerant found in some air conditioners uses R-410A refrigerant that has the ability to run operating pressures in the 700 pound range. A new set of refrigerant pressure gauges and hoses that are designed for old refrigerants only have a rating of about 650 pounds!

All HVAC technicians have to purchase new pressure gauges and matching hoses, not to mention new EPA-required refrigerant recovery equipment. If they don’t, someone will get hurt for sure! We wrote this article as a guide only and we strongly recommend that you call in a reputable HVAC service professional to repair your gas, electric or oil furnace and your gas or electric heat pump or air conditioner. So with all that said, we will try to write this page with an 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 tips listed as “For Advanced Troubleshooting”.

OVENS:

DESCRIPTION: Oil heating, natural gas, LP gas and electric strip.

Most older gas ovens tend to have a pilot that lights up 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 that use pilot generators, which are totally different than the thermocouples used in standard 24-volt furnaces. The thermocouple can fail thus providing a safety against the furnace attempting to send raw gas to the burners with no pilot present. If your pilot does not stay lit even though you have followed the pilot lighting instructions generally posted inside the oven 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 period, release the knob. The pilot should stay lit. If it stays on, turn the knob to the “ON” position. Burners should light if power is on and thermostat is calling for heat. If the pilot goes out immediately after you have pressed the knob for (2) minutes, you probably have a faulty thermocouple. This is the number one call we get on these old ovens. Various electronic pilots are also used, especially in older furnaces such as the following, Bryant LH33WZ512A Spark Ignitor, Carrier Pilot Burner. However, be aware that a faulty gas valve or open high temperature limit control can sometimes cause similar reactions.