is circulated by fan coil pump 64 to heat exchange coil 68 before returning to the tank through line 63 return air 66 is forced through coil 68 by blower 61 to temper supply air 67 in spring and fall tank 50 is biased toward cooling heat is supplied if necessary by electrical resistance heat strips 69 in fan coil 60 system logic prevents delivery from tank 50 of chilled water during heating conditions and hot water during cooling conditions as described below operation of the fan coil pump 64 is controlled by a lockout switch 62 which selectively actuates the pump 64 microprocessor controller 80 determines rctes operation and also provides an interlock or prevention mechanism to prevent counterproductive operation of fan coil 60 i e demand for heat when the system is in the cooling mode or demand for cooling when the system is in the heating mode controller 80 uses input data provided by sensor signal wires or connections 71 through 76 from level sensor 81 in tank 50 and temperature sensors 82 in tank 50 83 in tank 20 84 in outdoor air 85 at the midpoint of coil 44 and 86 in the compressor crankcase to determine operation of compressor 10 via power wire 91 crankcase heater.