What it is
The thermostat sends 24 V signals to the furnace or outdoor unit. Goodman's AC manual says to check for a signal fluctuating between 24 V and 0 on R and Y, and to check the thermostat and its wiring, for short-cycling code 03. Carrier says to disconnect thermostat leads to isolate a short on furnace code 24.
How to choose
- Check what your system needs first: wire labels (R, W, Y, G, C and others), heat pump or furnace-and-AC, single or multi-stage, and whether you have a C (common) wire.
- Basic programmable models do not suit every system; read the compatibility notes on the listing and your system manual.
- Photograph the old wiring and terminal labels before disconnecting anything.
How it is tested
- Goodman says that if the voltage between R and Y fluctuates between 24 V and 0, check the thermostat and its wiring and repair or replace as needed. That check is written for technicians.
Replacing it
- Turn off power at the breaker before touching thermostat wires, move each wire to its matching terminal letter and follow the new thermostat's instructions. Call a technician if your wiring does not match the letters or you have no C wire.
Capacitors can hold a charge after the power is off. Safety terms.
Where to buy
These are Amazon links. Product page links go to one specific listing whose title we read on Amazon; we do not say it fits your model. Search links open search results, which change. Always confirm your model number and the part number in your manual.
Product pages
Searches by type or size
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Codes that mention it
Error codes whose own causes or steps name this part or check.
Goodman
Amana
Carrier
Per-brand lists: Goodman AC / heat pump · Amana furnace · Carrier furnace.