Air Conditioner Circuit Board Troubleshooting Question - Hello, my name is Calvin and I am an HVAC Technician that graduated from a community college 2 years ago and I am still learning and know I have much more to learn before I think of myself as an expert. I have been running into a lot of circuit boards in air conditioners and heat pumps and I simply want to know what is the best way to troubleshoot and air conditioner circuit board? It seems like a lot of electronics and they never covered electronics too much in school.

Hello Calvin and thank you for the great comments about our website. We sincerely appreciate it! It is good that you have the attitude that you have about continuously learning new things. You could work in this industry for many years and still not know everything so keep it up and keep sharpening your skills and it will carry you far. I have seen so many technicians who think they know everything and end up being humiliated and/or frustrated because of their over-confidence.

As far as troubleshooting circuit boards for air conditioners I use one simple rule to make things easy. Since we do not have an electronics lab or electronic parts (aside from carrying a few resistors for discharging capacitors) that we carry on the service van nor do we have any of this at the shop then you have to make a decision after checking everything else out and knowing the board is bad. I know you mentioned air conditioners and heat pumps, but this also applies to gas furnaces. There are many gas furnaces that use circuit boards to control the ignition process and other parts of the gas furnace. ECM blowers are also controlled by circuit boards so you can apply this information to many other components and equipment types within HVAC.

Air Conditioner Circuit Board Troubleshooting Guide

1. Always check to make sure everything in the system is working properly or not malfunctioning. Start with the basics and work your way to the problem. Of course, depending on the problem will depend on where and what you look at. This is true for air conditioner troubleshooting, heat pump troubleshooting, or gas furnace troubleshooting.
2. A circuit board in the most common system works off of input and output. First, make sure you have power to the board. In some cases, this will be line voltage and other cases the board will get its power from the control transformer. Either way, check to make sure you have the proper input voltage to the board.
3. Next, you want to check the output and this is a little more involved than the previous step. Many air conditioner circuit boards rely on a safety check before it sends an output signal or voltage to the device it is controlling. There is usually a check through all the safety circuits before the board will allow an output signal. The most common of these are limit switches and pressure switches. If any of those switches are open then the board will not allow an output signal to the device it is controlling. Some boards you jump out the safety circuit and if the unit starts working properly then you know there is a problem in the safety circuit that needs to be addressed. Note: Whenever you find a problem in a safety circuit never assume it is a bad switch. Always look for a problem that caused the switch to open. This is very important, especially for furnaces. This step involves a clear understanding of an air conditioner sequence of operation and air conditioner components. Of course, if it is a heat pump or furnace you should understand the sequence of operation and components of those systems also. And always remember, while some equipment has similarities, not every single piece of equipment is the same and will vary for components and sequence of operation especially gas furnaces.
4. If you do not find any issues, after all that, then you can kill the power and carefully remove the board from its mounting pins or bracket and look at the back of the board. Many times I have seen something burned out on the circuit board by observing the back of the circuit board. In that case, you need a new circuit board to solve the problem. Depending on the complexity and connections to the board, take a photo of it before you disconnect anything. This will give you reference when reinstalling of all the terminations. In some cases, manufacturers make the board connections/terminations idiot proof by using one-way Molex connectors/plugs.
5. The little black cubes you see on the air conditioner circuit board are typical relays that will energize a fan motor such as a blower motor or a condenser fan motor. If the fan fails to energize and there is no output from the air conditioner circuit board take a screwdriver and using the handle of the screwdriver tap the little black cubes on the board (on a call for heating or cooling of course). Sometimes the relay contacts inside the little black cube will stick and with a little tap they release and close (or open if the fan motor will not stop when not calling for operation). In that case, you need to replace the air conditioner circuit board otherwise, the problem will continue.

Air Conditioner Circuit Board Troubleshooting Conclusion

It is really basic input and output. You must have the proper input to get the proper output. I have a customer where I found a bad board with burn marks on the back. The part of the board that burned out controlled the blower motor. It was a very hot summer and I did not have that board on the truck and it was a very good possibility they would have to wait a few days for me to order and get the board delivered. I simply bypassed the board for the blower and made the blower run all the time. While the blower ran all the time everything else was controlled normally through the board. I could have hooked up a relay and made it work there but I asked the customer what they wanted and gave them their options. They told me it would be okay to run the fan all the time but they wanted the system fixed with a new board. So if you find yourself in a similar predicament Calvin, you can always bypass the circuit board to make things work just remember to never bypass any safeties in the system. Good Luck!!

PS…..you can use our search feature here to find other troubleshooting and sequence of operation information for different types of HVAC equipment. We are currently building a cross-index compendium for all of our articles to make it easier to find various related articles.

Air Conditioner Circuit Board Troubleshooting

Air Conditioner Circuit Board Troubleshooting