Freeze-up control for air heating and cooling system

Claim 1

AN AIR CONDITIONING SYSTEM COMPRISING: A HEAT EXCHANGER IN THE AREA TO BE CONDITIONED, A REFRIGERATION SYSTEM INCLUDING A COMPRESSOR, CONDENSER, AND AN EVAPORATOR IN OPERATIVE RELATIONSHIP TO COOL A FREEZABLE HEAT EXCHANGE MEDIUM, A FIRST CONDUIT MEANS TO SUPPLY COOL HEAT EXCHANGE MEDIUM FROM SAID EVAPORATOR TO SAID HEAT EXCHANGER, A SECOND CONDUIT MEANS TO RETURN HEAT EXCHANGE MEDIUM FROM SAID HEAT EXCHANGER TO SAID EVAPORATOR, A THIRD CONDUIT MEANS INTERCONNECTING SAID FIRST AND SECOND CONDUIT MEANS, A SOURCE OF HEAT TO HEAT A HEAT EXCHANGE MEDIUM, A FOURTH CONDUIT MEANS TO SUPPLY HOT HEAT EXCHANGE MEDIUM TO SAID HEAT EXCHANGER FROM SAID HEAT SOURCE, A FIFTH CONDUIT MEANS TO RETURN HEAT EXCHANGE MEDIUM FROM SAID HEAT EXCHANGER TO SAID HEATING MEANS, VALVE MEANS OPERABLY ASSOCIATED WITH SAID HEAT EXCHANGER TO SELECTIVELY PROVIDE HOT OR COLD HEAT EXCHANGE MEDIUM FROM SAID FIRST AND FOURTH CONDUIT MEANS TO SAID HEAT EXCHANGER, A HEATER IN SAID THIRD CONDUIT MEANS, AND THERMOSTATIC CONTROL MEANS OPERABLY ASSOCIATED WITH SAID HEATER TO ACTUATE SAID HEATER IN RESPONSE TO A CERTAIN PREDETERMINED LOW TEMPERATURE TO CIRCULATE WARM HEAT EXCHANGE MEDIUM IN SAID THIRD CONDUIT MEANS, DURING PERIODS OF NONUSE OF SAID EVAPORATOR.