Help diagnosing HVAC

[mnoeltne]

OK, first, I admit it, I screwed up and probably caused this problem.

I changed out our thermostat over the weekend. We had a 5/2 programmable with manual heat/cool switching, and I changed over to a 7 day programmable with auto heat/cool. Both were Honeywell thermostats.

I did this early in the morning while my wife was cooking breakfast, and I wasn't 100% awake and forgot to hit the kill switch on the furnace to kill the power.

I changed out the thermostat and now the AC doesn't work. I've checked the wiring, and I swapped back to the old unit to verify that it wasn't just a bad thermostat.

Even though I was careful and didn't see any sparks, I'm guessing I touched two of the wires together while doing the swap. Who knows which two it may have been.

My question is what did I likely burn out? Any quick checks I can run (voltage readings at certain points, etc) to see what is up? It will be a few days before I can get the local HVAC guy out, so I'm looking at what I can do in the meantime.

This is new construction. I was upgrading the thermostat from what the contractor installed. It's a Rheem gas furnace and AC, brand new. And Honeywell Pro 4000 thermostat initially installed and back in place now.

 

[Brian_WK]

Check at the furnace (remove covers) for any lit up leds on the board, with the safety switch for the door pressed in. No lights looks for a automotive blade fuse on the board. Remove it and check that it isn't blown.
Report back if that's not it.

Brian

 

[mnoeltne]

OK, can't do that until I get home tonight. Thanks for the suggestion!!

 

[BD1]

Neighbor did the same thing and blew the low voltage side of transformer as mentioned. I prefer the old basic ones, you guys can have that programmable junk. Nothing but issues with them. Neighbors battery died in the winter while on vacation in Florida. House water froze and split, nice swimming pool in basement.

 

[mnoeltne]

OK, no lights, so I located a fuse and it looks like it's blown.

It looks like an automotive fuse, but is purple and marked with an E or 3. Is this going to be something HVAC specific? Or can I find them at HD or similar?

Is there likely to be a problem with other things? Or is it likely that replacing this fuse will solve my issues?

Thanks for everyone's help!!

Edit: looks like 3a and Amazon has them, but HD doesn't show them on their site.

 

[dreasoner]

That is probably a 3 Amp fuse. Auto parts store or big box store should have them. Check wiring diagram. Blade fuses are colored coded as well.

 

[dreasoner]

Replace fuse and see what works.

 

[arsco]

look into R/RC on your tstat. if you have 2 xfrmers you need to split them on the stat

 

[dreasoner]

You mean RH/RC? Most new equipment is single transformer.

 

[mnoeltne]

OK, I replaced the 3A fuse. I almost thought it wasn't going to work, but about 5 minutes after turning things back on and adjusting the temp to force the system on, and it's now running!!

Thanks everyone! Garage Journal, as usual, has been a big help!

 

[Brian_WK]

OK, I replaced the 3A fuse. I almost thought it wasn't going to work, but about 5 minutes after turning things back on and adjusting the temp to force the system on, and it's now running!!

Thanks everyone! Garage Journal, as usual, has been a big help!

Glad to help.

Brian

 

[joel63]

OK, I replaced the 3A fuse. I almost thought it wasn't going to work, but about 5 minutes after turning things back on and adjusting the temp to force the system on, and it's now running!!

Thanks everyone! Garage Journal, as usual, has been a big help!

There is a 5 minute timer in the control board (or the thermostat) that prevents the system from short cycling. It's mainly protection for the compressor.

Glad you fixed it. NOW, remember to turn off the power to the system before proceeding with any future repairs.

 

[mnoeltne]

Yeah, I normally do that on ANY device that I'm working on. I just had a brain f*rt that morning.

I guess that means that I'm just human.