use a multimeter to check for a microamp (µA) signal

If the air handler is blowing cold air during a call for heat (W1/W2)

when you're spec'ing out components for reliable thermal protection

0 µA while the flame is touching the rod

a failed condenser fan motor

Danfoss 193B-1535 4 Way Valve 30067439-890 use a multimeter to checkThe Danfoss 193B 1535 4 way reversing valve is a heavy duty brass component engineered for high capacity heat pump and air conditioning systems. With a 29. 3 CV flow coefficient and 1 1 2 inch ODF connections, this valve provides precise refrigerant flow reversal with minimal pressure drop. Designed for peak volumetric efficiency, it utilizes a pilot operated sliding block mechanism that ensures reliable performance even under high differential