Ruud air conditioner thermostat display is blank and system does not respond.

Safety first: Turn off power to the indoor unit before accessing the control compartment.

• Step 1 – Check indoor unit power: Ensure the furnace/air handler breaker is ON and any service switch is ON.
• Step 2 – Inspect low-voltage fuse: Locate the 3–5A fuse on the Ruud control board. Replace if blown with the same rating.
• Step 3 – Look for shorts: Inspect thermostat wiring at the thermostat, air handler, and outdoor unit for bare wires touching metal or each other.
• Step 4 – Check float switch: If a condensate float switch is wired in series with the R wire, ensure the pan is dry and the switch is closed.
• Step 5 – Transformer test: A technician should measure 24 VAC output from the transformer. Replace if no output is present.