No Heat, Boost Gauge Reading Zero, and Overheating - Disconnected Vacuum Line

Vehicle had no cabin heat from HVAC, boost gauge was reading zero, and the car was overheating. All three issues appeared simultaneously on a 7M-GTE.

A vacuum line running from the rear of the intake manifold to a T-fitting was disconnected. This single vacuum line feeds the boost sensor, cruise control, and the hard vacuum line along the firewall that connects to the heater control valve. The line had been accidentally disconnected during starter removal from above and was tucked back out of view. Loss of vacuum to the heater control valve prevented the valve from opening (no heat), loss of vacuum to the boost sensor caused a zero reading, and the vacuum leak likely caused air pockets in the cooling system leading to overheating.

High confidence — Original poster confirmed this resolved the issue