I have a large McQuay air handler (LSL141DH) that vibrates / pulsates when the VFD ramps up (>50 Hz). If I open the door at the blower side (downstream of the coil) the vibration / pulsation stops. It “appears” that the vibration is the greatest at the discharge vent of the air handler. The walls in the offices adjacent to the machinery space also vibrate. No vibration is felt at the concrete pad.
Question: If an air handler is not getting a sufficient return air flow, can it result in vibration / pulsation of the air handler or discharge ventilation? If so, what would be the theory behind it?