AC Not Turning On
When a Dallas AC goes completely dead in the middle of summer, the cause we run into most is a tripped condensate float switch - a small safety in the attic that cuts all power the moment the drain backs up, which happens constantly in our heat and humidity.
The split is between power and controls. If nothing responds at all - no blower, no click, a blank thermostat - work through the power path: the breaker, the fuses in the outdoor disconnect, the thermostat batteries, and that float switch sitting on the drain pan in your attic. If the thermostat instead lights up and calls for cooling but the equipment stays silent, the fault has moved downstream into a control part - a failed capacitor, a burned contactor, a dead low-voltage transformer, or a corroded control wire.
Most of what kills power to a system is inexpensive to put right - a float switch, a capacitor, a contactor, and a transformer are all small parts. The costly exception is the compressor. If the outdoor unit only hums or clicks and then trips the breaker, the compressor may be seized, and that's the point where the age and refrigerant type of your system decide the outcome: replacing a compressor in an older R-22 unit rarely makes financial sense next to a new system, while a newer unit under warranty is a different calculation.
Our climate loads the deck toward a few of these. Long, humid summers grow algae and sludge in the condensate line fast, and once it clogs the float switch does its job and shuts everything off - a nuisance that's really preventing water damage to your ceiling. The expansive clay soil under North Texas homes shifts with the seasons and can loosen a disconnect connection or a control wire over time. And after a hard winter like February 2021, freeze damage on the heating side sometimes surfaces as a system that simply won't start back up.
How we pin it down
- Check the breaker and the fuses in the outdoor disconnect
- Verify thermostat power, batteries, and that it's set to cool
- Inspect the attic float switch and drain pan for a backup
- Test the capacitor and contactor at the condenser
- Check the low-voltage transformer and control fuse
- Watch the compressor's start behavior and amp draw
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Frequently asked questions
My AC is dead but the breaker hasn't tripped - what else cuts the power?
Plenty can, short of the breaker. The most common in our area is the attic float switch shutting the system down because the condensate drain clogged. Dead thermostat batteries, a blown low-voltage fuse, or a failed transformer will also leave everything unresponsive with the breaker still on. We trace power from the panel forward to find where it stops.
Why does my system keep shutting itself off in this heat?
A system that repeatedly cuts out is usually protecting itself. In Dallas summers the frequent cause is the condensate safety switch tripping as the drain slowly backs up, but an overheating compressor or a failing capacitor can also force shutdowns. The pattern of when it quits helps us narrow it down.
Is a dead compressor worth replacing on an older unit?
That's the honest fork in the road. A compressor is the priciest part in the system, so on an aging R-22 unit the cost of the part plus scarce refrigerant often rivals what a new, more efficient system would cost - and the new system comes with a fresh warranty. On a newer unit, especially one still under warranty, a compressor swap can be well worth it. We lay out both paths.
Could last winter's freeze have caused this?
It can. A hard North Texas freeze can crack a component or stress the heating side, and that damage sometimes doesn't reveal itself until you call for cooling months later. If your system quit at the first summer startup, freeze-related damage is one of the things we check.
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