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Bill P.
Bill P., HVAC Mechanic
Category: HVAC
Satisfied Customers: 338
Experience:  Oil / Gas / A/C / Hydronics
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My Carrier AC thermostat has blank screen

Customer Question

My Carrier AC thermostat has blank screen tonight. It was just working and now is blank

Make : Carrier
Model : not certain

Already Tried:
Pushing buttons and opening the case of thermostat

Submitted: 4 years ago.
Category: HVAC
Expert:  Bill P. replied 4 years ago.

Bill P. :
Hi there
So the thermostat just went dead?

JACUSTOMER-04wvd0fm- :
yes

Bill P. :
Let's do some troubleshooting here. Were you adjusting it when it went blank?

JACUSTOMER-04wvd0fm- :
no.. the a/c was running then stopped.. when it didn't turn back on I went to adjust the temp and the screen was blank

Bill P. :
does the thermostat have slide buttons for "cool/off/heat" and "fan auto/fan on" ?

Or are they rubber push buttons, actually it would help if you could find the model of the thermostat

Have you had any storms, power surges pass through?

JACUSTOMER-04wvd0fm- :
Rubber push buttons
no storms

Bill P. :
is it a model with batteries in it?

JACUSTOMER-04wvd0fm- :
checking... electrical
checking the breaker

Bill P. :
some thermostats run on their own batteries, but some need power from the furnace to display

JACUSTOMER-04wvd0fm- :
It is wired into electrical system... just reset breaker with no change

Bill P. :
what type of system of this, normal inside furnace, outside a/c unit?

JACUSTOMER-04wvd0fm- :
A/c on roof

Bill P. :
is this a comercial unit then?

JACUSTOMER-04wvd0fm- :
Residential "Carrier"

Bill P. :
where is the air handler unit? somewhere you can access it? (the indoor blower)

JACUSTOMER-04wvd0fm- :
It is on the roof... ducted into house

Bill P. :
ahh ok, i'm just completely guessing here without a model number for anything. Did you find whether the thermostat has batteries or not?

JACUSTOMER-04wvd0fm- :
The thermostat is wired into the electrical system.. NO Batteries.. I have all paperwork for thermostat here.. looking for model #

Bill P. :
On this system the thermostat is getting its power from the outside unit. you have already checked the breakers for the unit, is there any switches of cutoff switches/boxes that could be shutoff?

if power is getting to the unit, then it could be a low voltage transformer burnt out, or the low voltage automotive type fuse on the control board blown

JACUSTOMER-04wvd0fm- :
No- It has 24VAC

Bill P. :
the thermostat does?

JACUSTOMER-04wvd0fm- :
yup... reading from the instruction manuel

Bill P. :
hmm ok good, i didnt realize you had tested it

JACUSTOMER-04wvd0fm- :
for Carrier Heating and Cooling Programmable Thermostat

Bill P. :
are you saying is does have power or its supposed to from what the book says?

JACUSTOMER-04wvd0fm- :
I didn't test it I am just reading from the manual which states " requires 24VAC to be coonected for proper operation

I don't have ability to test or troubleshoot - don't know what 24VAC is

Bill P. :
ok, 24vac is the low voltage that the contol side of you system works on

Besides checking all switches etc. that you have access to, there isnt alot you can do without getting in there and troubleshooting

JACUSTOMER-04wvd0fm- :
so no batteries right?

Bill P. :
no batteries by the sounds of what you mentioned there

JACUSTOMER-04wvd0fm- :
Is there a fuse on the unit on the roof that I should check?

Bill P. :
is it easy access for you to get to the roof or no? you could look for a blown fuse but even that would involve taking a panel off etc.

in your paperwork is there anything about the model of the outside unit?

JACUSTOMER-04wvd0fm- :
I did not find any. I will go up on the roof and look at it

Bill P. :
try and find there a smaller (usually brown) wire goes in
1/2 inch or smaller

however it could be in a conduit and you wont be able to see it. We are looking for where the thermostat wires hook up to a control panel

on that panel somwhere (or in its own small holder) should be a auto type fuse

(turn power off of you are going to start poking around taking a panel off..

JACUSTOMER-04wvd0fm- :
OH good idea

Bill P. :
sorry im talking about 2 different panels, one i mean like a access door, and the other a control board

you will need to take a door off to get to any wiring likely, then have a look around

have a look at any wiring you see, for any burnt wires or melted wires

JACUSTOMER-04wvd0fm- :
Going to take fuse to Lowe's to get new one.. kind of brown through glass window...??

Bill P. :
ok good luck, get more than one

Bill P., HVAC Mechanic
Category: HVAC
Satisfied Customers: 338
Experience: Oil / Gas / A/C / Hydronics
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