141 results in a situation where the air leaking into the system is at 95 humidity and the air expelled through the vent 141 is at 100 humidity the difference of 5 relative humidity represents a very small volume of water being lost there may be circumstances in which it is desirable to accept this relatively low rate of coolant loss for example to permit use of the system even where the heat exchanger 114 the level switch 134 or the valve 132 is broken in the disclosed embodiment there is a not illustrated sight glass which is a vertical glass tube that is in fluid communication with the flow loop for the coolant by looking at the level of coolant within the sight glass a determination can be made of the extent to which the amount of coolant in the system has decreased for example through loss of small amounts of coolant vapor through the vent 128 or the vent 141 more liquid coolant can then be added to the system alternatively it would be possible to calculate the required amount of make up coolant with the aid of a psychometric chart and with knowledge of the flow rate and temperature of the vapor saturated gases leaving the tank 126 through the vent 128 the provision of the heat exchanger 114 helps to convert as much of the coolant as possible to liquid form thereby minimizing the amount of coolant lost through the vent 128 which in turn.