Abstract: PCT No. PCT/US 79/00837 Sec. 371 Date Oct. 10, 1979 Sec. 102(e) Date Oct. 10, 1979 PCT Filed Oct. 10, 1979Pneumatically operated control mechanisms (10-18) for vehicles have often been found to leak control fluid during start-up in extreme cold conditions until attaining normal operating temperature. It has been discovered that the problem lay in loss of resiliency of poppet valves (21) because of the exposure of the elastomer seals (24,26) to extremely cold ambient operating conditions. The problem has been solved by heating the incoming air. Reliable heating is accomplished under extreme cold conditions by use of a fluid heater (40) having an elongated heating member (41) and inner and outer sleeves (48,51) around the heating member to provide inner and outer annular spaces (49,52) through which the fluid to be heated flows in counter-current directions.