Tech found thermostat reading 70 with actual temp at 75. Tech recommends replacing thermostat. Tech replaced thermostat and insulated the hole behind the thermostat that was bringing in cold air. Thermostat is now showing the correct temperature. Tech tested in heat and cool modes and found AC not working and heat only working in Emergency Heat due to no high voltage at the condenser. Fuses were good, but disconnect not receiving voltage. Tech found the main breaker tripped. Tech turned it back on and found unit running, but could hear breaker popping and tech shut it back off. Tech recommended calling an electrician to determine if the breaker needs to be replaced. 3 pole commercial breaker. Manager has been notified.