Mueller A17921 Manifold 320788-703 a hum with no startup

a hum with no startup (often a failed capacitor or seized shaft)

and phase imbalance

Always verify the 4 cell gasket configuration against your specific furnace model number before installation to ensure total pressure switch stability and combustion safety

Ensure the porcelain is clean of carbon deposits

or if the system exhibits rapid cycling

Mueller A17921 Manifold 320788-703 a hum with no startupThe Mueller A17921 ReliefMaster is a heavy duty change over manifold engineered for high demand industrial and commercial refrigeration applications. This HVACR manifold features a 1 2" NPTFE (National Pipe Thread Fuel Extended) inlet and 1 2" NPTFI (National Pipe Thread Fuel Injection) outlets, providing a secure, leak proof transition for dual relief valve setups. With a design pressure (MAP) of 700 psig and a broad operating temperature range of