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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.
Air Conditioner Circuit Board Troubleshooting
Air Conditioner Circuit Board Troubleshooting Answer
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. They end up being humiliated and frustrated because of their over-confidence.
As far as troubleshooting circuit boards for air conditioners, I use a straightforward rule to make things easy. 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. Neither do we have any of this at the shop. Using the process of elimination, you can come to the conclusion that the board is bad.
I know you mentioned air conditioners and heat pumps, but this also applies to gas furnaces. Many gas furnaces use circuit boards to control the ignition process and other parts of the gas furnace. Circuit boards also control ECM blowers. So you can apply this information to many other components and equipment types within HVAC.
Air Conditioner Circuit Board Troubleshooting Guide
- 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 issue will depend on where and what you look at with the system. That is true for air conditioner troubleshooting, heat pump troubleshooting, or gas furnace troubleshooting.
- 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 in 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.
- 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 correctly, 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 an issue that caused the switch to open. That 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.
- 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. That will give you reference when reinstalling all the terminations. In some cases, manufacturers make the board connections/terminations idiot-proof by using one-way Molex connectors/plugs.
- 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.
Dip Switches
Finally, some circuit boards have dip switch settings that may need manual settings. The rule with this is if something has changed or if someone has changed the dip switch settings inadvertently? To get the correct settings on the dip switches you will need the manufacturer’s installation guide and the specific technical information for the equipment being controlled. Some example of additional information can be:
- Tonnage
- CFM’s
- Dehumidification Sequence Options
- ECM Variable Speed Motor Options
- Staging Options
- Additional features such as a humidifier or electronic air cleaner
In some cases, the rocker switches on the dip switch board are tiny and difficult to see. You will either need a magnifying glass or use your smartphone to take a picture of the dip switch board so you can zoom in on the dip switch board and verify the settings are correct or align with the manufacturers settings based on the manual.
Air Conditioner Circuit Board Troubleshooting Conclusion
It is 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
Technical Resource: Refrigeration and Air Conditioning Technology
have an old (35 years) Trane American Standard Freedom 90 HVAC. the motherboard that controls the condenser fa n and refrigerant pumps etc has failed.had a pro diagnose this and i can see the black icky area. the pro said that that was the end of the line for this unit. according to him a replacement board simply did not exist. the alternative was a 7-10K rebuild. i was amazed and stunned. “control, motherboards, trane, hvac” google searches revealed a world of motherboards as well as highperformancehvac.com. and the board that looks most like mine is seen in the video on this page. so i have yet to remove the board and bring it in so that i can compare oranges to oranges. i will carefully follow your protocol of photoing all the things i remove and then keeping the wires basically where they are. i think i am on the right track but is my pro correct? is there no possible way to find a replacement for this board? thanks so much great website!!!
I would call another dealer to see if they have the board. Sometimes techs want you to replace the whole system because they get a commission or spiff from selling a new system to someone. I know it’s dishonest and I abhor it but what can you do?
Another option is to take the board to an electronics shop and let them repair it. I seriously doubt it would cost 7 to 10k to do that.
And if it’s only for the condenser only then you have a heat pump and that is a defrost board unless it is a really old two-stage system. Either way, good luck and hope you get it fixed.
Hi
Rheem H1V2417STANJA – When thermostat calls for cooling the unit start in low 700 cfm for a approx. 2 minutes then ramp-up to 900 CFM for 1 minute or so and the the entire unit stop. After approx. 4 minutes the entire cycle start again.
Why does my zone board temp go so low the low temp light comes on and the condenser unit shuts off After a couple of minutes the condenser 7nit come back on . A couple of minutes later it shuts off again and the zone board says low temp
Hello, I have a Carrier air blower unit with a bad circuit board and a blown bryant thermostat which was caused by a power serge from the street level. simple question if the circuit board is no good would that prevent the thermostat from having normal power to turn on?
Yes, that is possible. A quick test with a multimeter will tell you. You should have 24-volts from R to C. If no 24-volts then either the transformer or the board is bad. If you have 24-volts then the thermostat is bad.
had a step down transformer replaced it was fried by a surge last fall.Tech was surprised it didn’t take out mother board also. Turned ac on today and only the fan motor runs. No cooling at all. Is the board finally kaput.
It is possible but it could be something else. You need a tech to troubleshoot it.
Live in Charlotte, NC. First hot day Saturday, high 91. The heat pump fan was not running, the air handler just recirculating air. Called our service provider. They came out and could not find a problem with the unit. He just flipped circuit breaker on and off. Then about thirty minutes after communicating this to us, the tech came back and said, “as he was putting the screws back in the heat pump it switched off again”. Said we needed a new circuit board and would have to order. It is two days later and the unit is running fine. Are we being scammed. The cost of this repair is over $800. including the part. Our service provider provides incentives for techs with the highest sales. 🙁
If it has been running fine for two days I would tell them to keep the board in stock if it does it again. Beware of service companies that give their techs commissions. It is a recipe that goes against the consumer.
AC won’t cool. Lennox model. The LED lights flash correctly for cooling, fan, and heat operations. The outside unit appears to be operating (Fan operating). The thermostat works. The copper refrigerant tube is cold to the touch.
Any ideas?
Before Calling Heating Cooling Repair Service – Checklist
Hi, currently we are using the 2hp air-conditioner and the timer(to switch if off) is always operated once we switch on the air-conditioner. We had reset the timer to normal mode, but yet it still back to its timer mode.
Do it have something to do with the circuit board? Do we need to change the whole board? pls advice.
Not sure about this………from what you are describing I would check the timer switch first to make sure it is functioning correctly. That would go along with checking all the electrical connections to make sure they are tight. After doing all that and making sure that was all good I would check the circuit board for proper input and output running through some functional tests.
Hi, anybody knows what’s the trouble of a split A/C when in runs for 1 minute or less then automatically shutdown though it’s set on LOW FAN MODE. Made it run on COOL MODE 20°C tubes got chilled but still the same trouble. Outdoor unit runs. YORK model HTEA180S-AARHere in Middle East temperature logs between 28-38°C April 2020.
Thanks.
Presumably had a relay go bad on the circuit board. We bypassed the relay to have the fan run all the time until new relay could be installed. After a day the fan motor will run, but only if the system itself is set to “off”. If I switch the system to “cool” on the thermostat the fan motor shuts off (outside unit still comes on). Any ideas? Should we replace relay or proceed to replacing the whole board?
Replace the board.
My LG window unit circuit board is reading E 1ican turn it on with remote but not on the panel and temp.is reading 30 and I can scroll it down to16 is the board bad
Have no idea………..every manufacturer is different with different codes. Try resetting the power and try it again. Then read the owners manual to see if you find more info. After that and still no luck, call an LG service provider.
My blower wont stop continuous 24/7 can you give me Idea what is the problem? The temperature I program like 72 deg. it will stop but the blower continuous.
If in the heating mode then you have a problem with the heating system if it is a gas furnace. It could also be a stuck relay in the board in which case the board needs to be replaced. Best to get a technician to look at it as replacing the board is more likely expensive than fixing the problem with the heating system if that is the problem.
it was really very helpful,giving me a clue on how to troubleshoot a/c pcb.