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Reads 24 V or less / transformer failing
What is going on
Possible causes and checks for: reads 24 v or less / transformer failing.
Likely causes
- Aging transformer
- Series loads dropping voltage
- Too many parallel loads (add-on humidifiers, air cleaners, zone panels wired off the furnace transformer)
- A load drawing over nameplate (contactors, time delays, fan relays, liquid solenoids, gas valves, zone dampers/valves, ignition controls, oil primaries, stats). Procedure: trace circuit, build ladder diagram, remove any series load, sum load amps × 24 V < transformer VA else upsize, clamp each branch (10-wrap trick), replace any load over its rating
- Listen for chattering. p.992–993 [966–967]
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