Wednesday, June 26, 2013

HVAC Troubleshooting Question

Recently we had responded to a question in one of the HVAC DIY forums. We like to share it here so our readers can read about it and learn something. Below is a portion of the message. "I started troubleshooting by making sure the condensate drain switch wasn't the issue and then did some tests with my multimeter. On the board I got 27ish volts across the heat, cooling, and fan terminals. At the t-stat I got... nothing. No reading at all on any of them. I jumpered R to Y on the board and everything runs just fine. House cooled down great. Jumpering at the t-stat wires didn't help anything. I've also swapped the board out with one I purchased at the recommendation of a service tech... there was no problem with the old board and it behaves the same way with both boards." In other words, the unit will not run at all when the writer jumps or hardwired R to Y at the thermostat but it runs just fine when he jumps it at the control board inside the furnace. Usually when something like this happen you want to check for loose wire or broken wire which breaks the 24V signal between the control board and the thermostat. This is exactly what happened in his case and all he had to do is just run a new set of wires. By knowing how the control works and by reading the control diagram of your a/c system you can easily troubleshoot thermostats, control boards and figure out which part might be wrong. Of course you should always let the professional handle it if you have any doubts but knowing a little about stuff like this can actually help you communicate with the pros. It is pretty fun to troubleshoot this kind of things especially when you found and fixed the bug.

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