Carrier a/c thermostat was working fine, then display went blank!

Every issue I've had with the Infinity has been a strange one. The blank screen is something I've seen and it was just a month ago. But I have no idea how I fixed it. Screen was blank but had the back light illuminated/was green but no numbers or letters displayed. I removed the tstat from its base, checked the pins on the back to see if any were bent or damaged. Tightened all wire terminals. Checked for 24v(present). Reinstalled to its base. Walked to my work truck and downloaded a manual. Walked back inside and the screen was now visable, with all numbers/letters present. I'm guessing I reset it by removing it from its power source? Also, at the indoor units' control wire terminal block, there is an A B C D. And most installers will connect 2 wires in each of these terminals. This is not correct and will give trouble due to a lost connection. You can try to tighten these low voltage terminals A B C D. The correct way to wire is at A, 1 wire is connected. That 1 wire is then connected to the 2 wires with a wirenut. B C D should be in the same way. 2 wires in this 1 terminal WILL lose connection and not communicate with the tstat. If this don't help, the tstat may need to be replaced. Hope this helps!

check fuse protecting low voltage transformer.

Hello, sometimes this happens when the condensate overflow switch trips duento a clogged condensate line. You need to find the outlet of the condensate pipe and use a wet/dry vac to clean it out. The pipe will be 3/4 inch PVC. Let me know what you find. If the drain is clear then the problem could be related to a burned out transformer or dead batteries if the thermostat uses batteries.

sounds like u might have a bad thermostat wire some where,maybe out by the condenser unit

YES IT CAN BE THAT SIMPLE / CHANGE THE BATTS FIRST AND USE NEW ONES
NOT FROM AN OLD TOY!!

Hi smargyle,

Welcome to fixya!

I can provide you with diagrams for the old Carrier therm and for the new Filtrete therm. But, I would need to know what the model numbers are for each therm plus how many speeds AC you have.

Please reply back with that information and we will get your AC back in working order.

Thanks,

Handie Andie

Hi,
The 24v transformer blew or if you are lucky there is a fuse in the line before the transformer...

Check in the air handler to make sure the cover is on right... then check for power to the air handler, then check ofr a fuse on the circuit board, finally check the transformer...

The problem lies in one of those things...

heatman101

Check the battery in the thermostat it is dead!! Should be 2 AA batterys!

The stat that works is called the main and the other two are called slave stats. The stats must be set to heat or cool the same as the main. If you want one room to cool and one to heat , sorry. Need to upgrade to auto changeover. Is this AC actally a Heat pump?

sounds like the batteries in the thermostat are weak is this a battery powered t stat