When facing a residential oil-fired furnace that is acting up, you want to get the situation under control as quickly as possible. A problem during the heating season will bring a call from an anxious and possibly agitated customer. The following are some of the most common issues that a service contractor addresses when troubleshooting an oil furnace, along with the possible cures.

Many service technicians often become confused when the liquid line becomes restricted in the refrigeration system. This is because the symptoms often look like an undercharge of refrigerant. This article covers a refrigeration system with a restricted liquid line after the receiver using R-134a as the refrigerant. The refrigeration system is a low temperature freezer with a receiver and a TXV.

A simple ohmmeter is all that is needed to troubleshoot a potential relay. After taking all of the connecting wires off of the potential relay, measure the resistance across the 1 and 2 terminals.

OK, you’ve exhausted all of the existing air from an interior space; now how do you replace it? You bring in makeup air from another source. For the purpose of an HVAC discussion, your source will be mechanical equipment — makeup air units.

Potential or “voltage” relays are used with single-phase capacitor-start/capacitor-run motors, which need relatively high starting torque. Their main function is to assist in starting the motor. Knowing the sequence of operation for this type of starting relay can help you diagnose, confirm, or rule out certain service problems.

There are four pieces to the refrigerant system diagnostic puzzle: suction pressure; high-side pressure; superheat; and subcooling. This article talks about subcooling.

The big push is on to replace R-22 unitary air conditioners and heat pumps, and it looks like the industry has really and truly decided that R-410A systems are “it.” This article offers an overview of some of the issues related to R-22 and -410A in the field: operating pressure differences, oil characteristics, and temperature glide.

Troubleshooting modern refrigeration and/or air conditioning systems requires a thorough knowledge of the refrigeration system and its functions.

The compressor’s discharge temperature can tell the service technician what is going on inside a refrigeration or air conditioning system.

Following up on Howard Leonard’s October 10, article, “Hidden Problems Can Cause Carbon Monoxide,” Leonard elaborates on the discharge side of the combustion air system, the flue.