Performed cooling maintenance tune up on Mitsubishi and Lennox systems checking all electrical components, refrigerant balance, cleaning of indoor and outdoor coils, treatment of drain lines. Testing of start up, operation, shutdown of both units. Everything looks and runs great on the Mitsubishi the Lennox unit is down estimating about a 1/4 of its refrigerant charge causing system not to keep up with cooling demand. Upstairs heating thermostat is about 5 degrees off and the cooling thermostat upstairs is accurate within .5 of a degree. Recommend replacement of mercury bulb round thermostat with digital thermostat for accuracy. Lennox unit may be able to limp along during summer months but may struggle on high cooling demand days.