Temporary Workaround Gets Cool Air Flowing Again While Waiting on Parts for an AC Repair in Johnson City, TN

We received a call from an existing customer in need of an AC repair in Johnson City, TN. They said that their AC unit was frozen up and that they couldn’t feel any air coming out of their supply registers. They stated that it was in the upper 80s inside their home. We advised them to turn the AC off so that the ice could defrost from the system and to protect it from burning itself up. We always advise to turn the system off if it is not working properly in order to prevent further damage to the system.

When we arrived, we fired up the AC system in cooling mode. We verified that the outdoor AC unit was turning on, but immediately noticed frost starting to form on the suction line of the copper lineset. We immediately went into the crawl space to the furnace and evaporator coil. We noticed that we did not hear the indoor blower motor running. We pulled the doors off the furnace and killed high voltage to the machine. We confirmed by hand that the blower motor was spinning freely inside. We tested the blower run capacitor and it tested within factory specifications. We restored power to the furnace and had high voltage and low voltage inside the machine. We had a low voltage call to turn the blower motor on so we tested high voltage to the indoor blower motor and we did not have any high voltage going through the integrated furnace control board telling the blower motor to turn on. We let the customer know that they needed a new integrated furnace control board.

We contacted the local supply house and the integrated furnace control board was not in stock. They had to order the board from the manufacturer because the furnace was almost 30 years old. Even with expedited shipping we were looking at 7 to 10 business days and we didn’t want to leave them without any AC. Since we were in cooling mode and the heat wouldn’t be needed in the middle of summer, we decided to bypass the board and wire in a high voltage relay in order to power the blower motor temporarily for cooling mode. We also temporarily disabled the heat call to the control board so that if someone accidentally did turn on the heat it wouldn’t hurt the machine. The G call in heat mode is controlled by the integrated furnace control board and the control board was bad.

One option was to put the blower motor straight to high voltage power and leave it running all the time, but that will increase humidity levels inside the home because the moisture that is pulled out of the home during cooling mode gets introduced back into the home when the Y call is not being received. We felt like a better option was to wire a temporary high voltage relay into the G circuit. This way when there was a call for G, the blower motor would turn on and when the G call was no longer needed the blower motor would turn off.

We wired the blower motor into the high voltage relay and controlled the relay with 24-volts. The low voltage control wires G & C went to the 24-volt coil and when there was a call for the blower motor it allowed high voltage to pass through the relay in order to turn the blower motor on. With this setup the blower motor operated more like the homeowner was used to minus the delay on break built into the control board. We could have wired a delay on break timer into the circuit as well, but it would have raised the cost on the repair, so we didn’t go that route. We left a detailed description of our temporary work around at the machine as well. Once everything was wired up, we fired the unit up in cooling mode and the customer had cool air coming out of their supply registers again. We verified that the system was operating in cooling mode with our temporary fix in place.

We received a call 9 days later from the supply house that the part came in and we picked it up immediately. We contacted the customer and swung by their home and replaced the integrated furnace control board, removed the temporary high voltage relay, and restored the heat call back to the board as well. We tested the system to confirm proper operation of the integrated furnace control board. We verified that they had a properly functioning HVAC unit that would now heat and cool their home as designed. If you reside inside of our service area of Northeast Tennessee and are in need of an AC repair, please feel free to reach out. Stay safe and best wishes.

Location: Johnson City, TN