My husband was installing a new digital thermostat because the first one quit having a display after the electricity being off for 2 weeks due to the hurricane. When we came back, there was no display on the old thermostat. Yesterday he put on the new one, and at the very end after working with if for over 2 hours to get the display to work on that one (it finally did) the red and black wires touched and sparked. He said that the breaker was off at the time of the spark. Now our brand new payne A/C is flashing a code 24 which means "secondary voltage fuse is open. check for short circuit in secondary voltage". What does this MEAN? I can't seem to find an answer anywhere? Is the A/C shorted, is it the wiring? Can we possibly fix it outselves? My a/c isn't messed up is it? We just bought it last month. I just would like to understand what has happened. Thanks in advance for any help. I really appreciate it.


Thanks,
Stacy

"Secondary" is referring to the secondary of your unit's transformer. Some transformers have a resettable fuse protection built into them but most OEM units don't. You should be able to pick up a new transformer at your local hardware store. Wiring it is pretty straight forward.

If you got a spark between 2 of the low voltage lines to the tstat, you didn't have the main system power (breaker) off. I assume that this 'code 24' is showing on the air handler somewhere. If not, I am going to need some other info before I can help you any farther.

The spark you saw was the short that blew the low voltage fuse in the AC system. On most recent units that have an electronic control board there will be a blade type fuse on that board (looks like a car fuse if you have an American car). Often it will have a 3 or 5 on it. If it isn't there, it could be a glass tube fuse mounted right on the low voltage transformer. This time turn the system OFF at the breaker. Pull that fuse (when it's out, you can usually see that the fuse element is gone) and replace it with an EXACT VALUE AND TYPE replacement. Make certain that no wires are still shorted in the tstat and turn it back on. If you had real bad luck, the board could be ruined. That WOULD be expensive.

EPM

What brand of furnace do you own? Shorting thermostat wires rarely ruin a control board. Or transformer, but is does happen. Most likey there is a fuse some where, we can help you locate the fuse if we get a model of the furnace.