Preheated Intake Air
From 1979 on, Volvos are equipped with a thermostat that controls the source of intake air during the warm-up period. The thermostat opens a flap that allows preheated air from the stove on the exhaust manifold to be directed through the air filter to the intake. The thermostat should close this flap soon after start-up and direct air, taken from behind the grille, toward the intake.

When the thermostat fails, hot air may be continuously supplied to the intake. On Volvos with LH-Jetronic fuel injection, this means hot air is passing through the air mass meter at all times. Failure to replace a failed air box thermostat may contribute to early failure of the more expensive air mass meter. On CIS injection Volvos, the hot air will richen the mixture and interfere with the correct operation of the fuel injection system.

Stocked at RPR:
Air box thermostat 240 79-93 -- 1266826
Air box thermostat 700 Turbo 85-92 -- 1266826
Other thermostats are sold only as part of the air filter box assembly.