So I had an interesting learning opportunity this weekend about heating, ventilation and air conditioning (HVAC) diagnostics and repair. Late Friday afternoon my wife noticed that it was getting warm on the main floor of our two story house so she went to the thermostat only to find nothing being displayed on the LCD.
I happen to be working from home that day so she calls me to look at the thermostat and solve the problem. After pushing the buttons and flipping the system off and on I do as any good problem solver does I turn to Google and begin reading articles and forum discussions and watching Youtube videos. The first step of most of the articles was to check the batteries in the thermostat. That sounded easy enough so I googled for my thermostat manual and followed the instructions for popping off the front face and replacing the batteries. The funny thing was when I got the front cover off the thermostat it didn’t have any batteries in it.
So clearly dead batteries wasn’t the issue, but just to be sure I put new batteries in the thermostat and it powered on. I turned it on to cool and ran the temperature down below the current room temperature so that it should have kicked on. Unfortunately the fan did not turn on so I went to the furnace unit containing the fan and checked the diagnostic lights. Surprisingly the lights were not lit so I checked what that meant in the instruction manual and funny enough there was no explanation for a scenario when the two diagnostic LED were not lit. There was slow blinking, alternating, fast blinking, both solid, one solid and one blinking, and a dozen other combinations, but no explanation when neither of the lights was lit.
So it was back time to pull out the Mastech multimeter and check voltages. I watched this YouTube video on HVAC thermostat wiring and troubleshooting which said that there should be 5 wires (R, W, Y, G, C) running from my furnace’s controller board to my thermostat. The controller board should be sending 24 volts along a certain combination of those wires depending on if it needs to signal heating, cooling, just fan, etc. It had been a while since I had used my multimeter so I watched this video from Sparkfun and read their tutorial as a refresher. Armed with my multimeter and knowledge of how to use it I checked all combinations of those 5 wires and got no reading. Next I checked that the switch for the unit was on. It was on and when I turned it off and back on I could hear the unit humming with power. Despite hearing the power energizing the unit I checked the circuit breaker box and flipped the breaker for the furnace off and back on just to be sure. The unit still did not work so I headed outside to check the breaker for the air conditioning units. These were on a separate panel on the side of the house. I flipped the breaker for the non-functioning air conditioning unit, but still didn’t get any response from the units. While investigating the air conditioning unit and the wiring running to it I discovered that the control wiring running from the furnace controller board to the air conditioning unit was in terrible shape. Someone had cut the control wire and spliced it back together leaving the individual control wires unprotected laying on the ground.
Whoever had done it had not taken the time to properly tape the splice with electrical tape and the coating around the individual control wires was falling off and the metal was exposed and touching one another on the ground. This could have easily caused the controller board to short circuit and be rendered inoperable which is how it appeared. At this point I called my dad for advice. After running through several of the same steps I had previously done we arrived at the fact that I may need to call a HVAC repairman. He recommended Air Heat America as he and his company used them in the past and had nothing but good things to say about them. After a little more research I called Air Heat America and didn’t expect anyone to answer since it was now 7:45 PM, but to my surprise they have a 24 hour paging service. They took my contact information and a brief description of my situation and said a technician would contact me shortly. Well sure enough within 30 minutes I got a call back from one of their technicians an Andrew Russell. I expected him to gather some information about the situation and schedule an appointment for the next day. To my surprise Andrew after hearing everything I had tried asked me to walk downstairs and check the fuse on the controller board. I had not seen the fuse on the controller board when I had been testing it previously and nothing I had read had mentioned a fuse, but sure enough when I pulled the fuse it was blown.
Next Andrew wanted to identify why the fuse had blown and asked me to check the control wiring leading out to the air conditioning unit. I told him that I had already come across the bare wires lying on the ground and he said that is what had caused the fuse to blow. He told me to run up to a hardware store or autoparts store and purchase a replacement fuse. Before putting the new fuse in I needed to cut the wires and re-splice them so that a short would not occur again. I thanked him profusely for his help and headed off to the hardware store. Unfortunately the fuse I needed was 3 amp and the smallest the hardware store had was 5 amp. It was after 9PM by this time and all the auto parts stores were closed so I headed back home disappointed at not being able to complete the repair, but with hope for tomorrow.
I headed out bright and early and got the fuse I needed at the auto parts store. I got back home and re-spliced the control wires and installed the new fuse. As soon as I pressed the door switch on the furnace the diagnostic lights lit up and the fan began spinning. I triumphantly put the furnace doors back on and headed to the thermostat to turn the temperature down to cool the house. The problem was I hadn’t heard the air conditioner come on outside. So I went outside and sure enough it was not running. Disappointed I began researching possible causes and came across these articles on how to check the air conditioner fuses, how to check the air conditioner capacitor, and how to check the contactor coil. When I checked the contactor coil points where the control wires came in I got no signal. There should have been 24 volts being sent from the furnace controller board. Not sure what to do next I called Andrew from Air Heat America and told him the situation. He patiently walked me through checking the water pump, the voltages on the controller board, the voltages on the air conditioner, checking the control wire connection into the air conditioning unit, and several other things. Unfortunately none of those led to the air conditioner coming on. At this point I had a sinking feeling that the problem was in the splicing of the control wires I had done. I cut the mound of electrical tape off and sure enough when I had used wire strippers earlier to strip one of the control wires I had used too small of a hole and cut through the wire. I re-spliced the wires again and before taping them up this time checked the voltage on the air conditioner. 24 volts as expected was the reading so I turned the power back on to the air conditioning unit and it immediately came to life. I thanked Andrew for spending so much time with me on the phone and being so patient. He said he was happy to help and that if I ever needed help again to just give him a call. It is not every day I come across that level of service, but when I do I have to stop and acknowledge it. So I am going to call Air Heat America on Monday and offer my sincere gratitude to the manager for all of Andrew’s help.
This was a wonderful learning experience as I have never worked on an HVAC system before. Having successfully fixed the problem I can say that I enjoyed all the research and taking apart my thermostat, furnace, and air conditioning unit. I feel confident that I could diagnose future issues with my system in a timely manner especially since I have documented my experience here so that I can refer back to it. I hope this proves helpful to anyone that comes across it and if you live in the Atlanta, Georgia area and need HVAC assistance I highly recommend you contact Air Heat America.