It finally got hot enough around here to turn on the A/C unit. I was happy when it fired right up and cooled down the house. When I woke up the next day,It was no longer blowing anything out of the registers.
The A/C unit is a Rheem 2.5 ton, the furnace is a Amana forced air. I have NG heat. The A/C unit is about 6years old.
I'm leaning towards the thermostat as the problem. I get nothing out of any control setting, no A/C, no heat,no fan only.
The thermostat has two AAA batteries, I replaced both, no change.

Is there another part of the controls for the HVAC system besides the thermostat that controls the various systems?

I didn’t see anything in your post about checking breakers.
Could be tripped out.

I have heat pumps so the Outdoor condensor is needed whether heating or cooling. #1 failure in my neck of the woods is the capacitor on the outdoor condensor.

Go outdoors to the AC condensor and see if it's making a noise like it's trying to start a fan, but the fan isn't starting.

If it's that, you need a new capacitor. Chinese ones are $20ish and made in the USA are $30ish (e.g. AMRAD sold on Amazon). They come in different sizes, but this is the one for mine.

I always keep it and/or a universal capacitor on my garage shelf so I don't get desparate and shell out big $$ locally during Houston's miserable summer.

I am BEYOND NOT AN AC tech, but saying even the fan only won’t run makes me think it does have something to do with the thermostat. I don’t know if you have an analog or digital thermostat. I once had a problem where the thermostat kept turning off and it turned out the condensation was not draining so it triggered a switch that shut off the thermostat so it would not keep running. Once I blew out the drain line with compressed air, all was good.

Other thing is as Tator said, which could be the capacitor.

Check the drip pan to see if it’s full of water. May have a plugged trap.

Thermostat calls for cooling, the 24v transformer sends current on the Y and R wires to the contactor (relay) and closes it permitting 240V to both the fan and the compressor, and the capacitor(s) are tied to the fan and compressor.

(some systems have one capacitor for the fan, and one for the compressor, and some have one that is a dual capacitor that handles both the fan and the compressor)

The air handler fan (in the inside unit) is controlled by the thermostat when the system calls for cooling and closes the relay on the circuit board in the air handler and supplies the 120v to the fan motor)

At the condenser, you should hear the contactor energizing as it makes a pretty loud click, similar to a car starter solenoid.

You can check the transformer to see if it is supplying 24v
use a multimeter set on AC and probe the Common and Hot terminals (marked C and R), if you have 24-28V the transformer is good.

If you don't have power, look for a small glass style fuse on the control board in the air handler and see if it has blown.

If it's good, check the primary (120v) side of the transformer (two 120v 14 awg wires) these will be controlled by the 20A breaker in the home fuse panel.


If all that checks good, open the breaker to the air handler and connect the Red Yellow Green (jumpers or wirenut) then turn the breaker on, and if the condenser unit fan/compressor come on, and the air handler fan comes on and you get cooling air, replace the thermostat.

If you have questions, post back.

The condenser has 24v and 240v, so just mess with the inside first.

And it is not uncommon (especially first start up of the AC season) for more than one thing to go wrong sequentially (cascading/symathetic failure) with contactors, capacitors and thermostats.

quote:

Originally posted by SIGfourme:
Check the drip pan to see if it’s full of water. May have a plugged trap.

Good easy first check. Especially since it hasn't been running. Dried crap in the drain maybe. Then the capacitor on the condensing unit.

quote:

Originally posted by SIGfourme:
Check the drip pan to see if it’s full of water. May have a plugged trap.

This is the first thing to check. At the air handler, you will see wires going into a PVC T on the condensate line. That’s a float switch that shuts everything off of the line gets clogged. Pull the float switch out, stick your finger in the hole to see if it’s full of water. If so, find where outside it drains and suck it out with a wet/dry vac.

There could also be a float switch in the drip pan as well.

I may have a different problem than yours. But two years ago, the A/C stopped working just like yours. I didn't know enough even though I had electronics / electrical training. Called HVAC company, they couldn't come out for a week. We stayed in a hotel cuz it was hot. Turns out, the fuse to the unit blue. It was outside in a box by the unit.

When mine goes out, it is almost always the filter. The system detects when the filter has reached its end of life and the unit shuts down.

UPDATE:

I checked the breakers in the beginning, no problem. My furnace has a drain for water directly tied to a floor drain, no water pan problems.I had changed the filter about 2 weeks ago.
I checked and found power to the circuit so that was good to go.
I changed the thermostat, problem solved.