This post is a general guide to HVAC troubleshooting. We won’t go into details that include local codes, OEM procedures and guidelines, or an in-depth analysis of terms like static pressure, superheat, or subcooling. However, in order to make an accurate diagnosis safely, it is imperative that you understand the basics of cooling/heating and electricity.
This post will focus on some of the hurdles to overcome before the next troubleshooting step. Some technical problems may take a few minutes, while others may take several hours or days, depending on the complexity of the problem.
Pro Tip: Before starting the troubleshooting, make sure that the appropriate PPE (personal protective equipment), safety glasses, gloves, etc. make sure it is installed.
To perform the diagnosis of any system, there are tools that will be needed during the process. One or a combination of the following tools will help you get a big picture of the problem at hand, let’s go through them one by one.
A compound manifold gauge set is used to test the system pressures of an air conditioning or refrigeration system. Also, if your manifold gauge does not include a scale for the refrigerant you are working with, you will need to use a pressure/temperature chart for the refrigerant used. Another option is to use a digital apparatus in the form of a manifold kit or smart probes. Digital gauges implement pressure/temperature charts inside and can be read from the screen or calculated using a mobile app.
Temperature Probe or Clamp
To control the superheat and subcooling of a system, you will need a temperature sensing device that can be installed in the system’s heatsink lines.
Since most problems are electrical related, multimeters will be used the most if any problem is encountered. A multimeter or meter combination should be able to check AC/DC voltage, amp draw, resistance in Ohm setting, capacitor microfarads, and DC micro amps of a flame sensor for basic troubleshooting.
Double Port Manometer
A manometer; It serves several functions such as controlling the gas pressure of the heating device, controlling the differential pressure between coils and filters, and controlling the static pressure of duct systems. Today’s manometers allow for options, we can choose a manometer with a display or a manometer that connects via Bluetooth to a mobile device.
A hygrometer measures temperature and humidity, and a wet bulb can give values such as temperature and dew point. This is a useful tool for checking supply air and return air, as well as outdoor and indoor air conditions.
Some other tools used for diagnostic purposes are:
- Combustion Analyzer
- Infrared Temperature Gun
- Thermal Imager
- Rotary Wing or Hot Wire Anemometer
- Electronic Refrigerant Leak Detector
GENERAL TROUBLESHOOTING STEPS
Step One: Customer Communication
If possible, contact the client before going out, have them explain to you what’s going on, have them record a video or take a photo remotely for reference when you arrive.
Note: Do not ask a customer to go beyond that, for example, open panels, reset limits, etc. Don’t risk your customer’s safety.
While on the road, create scenarios in your head of what could be wrong, with too many people falling into the trap of pre-diagnosis before they arrive and immediately trying to prove their guesses were correct. Instead, use a methodical approach, starting over to make sure nothing is overlooked.
When you arrive, analyze all the information the customer has collected for you. How long the problem has been present, when it happened, where it was, etc. learn. This will help you build a model of potential problems. If the customer has access to archived trend logs showing eg ambient/humidity or supply air temperature, ask to see it!
Step Two: Examine Using Your Senses
Note: Before entering a mechanical room, crawl space, basement, or attic using gas, propane, or oil-fired equipment… be sure to wear a personal carbon monoxide monitor for your safety.
Before using any diagnostic tool, visually inspect the equipment, looking for obvious things that can be corrected before continuing. For example, a dirty condenser coil, loose or faulty wiring, or improper ventilation. Examples include listening to strange noises, smelling burned bandages, or involving other senses, such as feeling vibration or using our hands to get an indication of pipe temperature. For reference, the palm of a human hand is roughly 33° Celcius. Anything that feels hotter than your hand is hotter than 33°C and vice versa.
Pro Tip: Before reaching the unit cabinets, ensure that the power has been removed and verified with a multimeter, locked if necessary.
Step Three: Verify Strength
After the initial inspection of the equipment, we must look at our primary power source, without the right power we cannot move forward. If there is no power, check the power supply for a circuit breaker or open fuse. For example, if the breaker trips, there may be a short circuit in the wiring or the primary load on the device. This should be fixed before continuing.
Note: An example of a primary load is a motor or compressor powered by the primary source fed to the equipment. As an example, the primary power of a condensing unit may be 220 V fed directly from the breaker panel.
When the primary power is restored and correct, we need to verify the presence of the control voltage or the secondary voltage. The control voltage can be found in many forms such as 24v, 120v, 208/230v and is usually fed from a step-down transformer. For this article, we will accept 24v.
Pro Tip: If you are dealing with primary power issues (breaker tripping when equipment starts up). It is recommended that you pull the “R” wire from the device low voltage terminal strip until the problems are resolved. This will prevent the equipment from starting up during the troubleshooting process.
Now that we’ve confirmed the primary and secondary power supplies are correct, we must move on to our control method. This can be a simple thermostat or a slightly more complex building automation system. Make sure the controller is powered, functional, and set up correctly.
Pro Tip: Defective thermostats can sometimes be diagnosed by bypassing them. Pull the thermostat from the sub-base and short-circuit “R” and “Y1” at the subbase. In this way, the thermostat is removed from the system. If the equipment starts to work, in most cases the thermostat has failed.
Fourth Step: Heat Exchange Environment
If we have improper airflow, we cannot exchange heat the way the system was designed to do. We need to make sure we have the right airflow or fluid flow before we move on to the next step. Make sure the fan or pump is running and most importantly spinning in the right direction. Make sure the air filters and inline strainers are clean.
Until we can prove the correct flow of our heat exchange medium, it’s a good idea to keep the system off for heating or cooling.
Pro Tip: If the fan or pump does not run during start-up, further troubleshooting will be required. For example, checking the power to the load and making sure it is correct, checking capacitors and relays or contactors if used. If the pump/fan is found to be faulty, it must be replaced before continuing.
If the system uses a relay board, you must ensure that the board receives an input and vice versa, transmits an output signal. In most cases, if the board is receiving an input and not providing an output, under normal circumstances, the board is usually faulty and will need to be replaced.