Evaporative System - Leak/Pressure Testing

June 1980

Issue: 6

Volume: 1

REMINDER OF THE MONTH




^ A pressure test per S.I. 01/79-343 (see page 84 of Section 2 of the Saab S.I. Supplement No. 1) is the only sure way to pinpoint evaporative loss system leaks. The bayonet-type filler cap on late model 900's is not as easily modified into an adapter tool for pressure testing as the earlier threaded cap. Instead, it is easier to disconnect the smaller tank vent hose at the tank and insert a short hose and tee-fitting to which you can connect the cooling system test pump. As described in the S.I., do not use high pressure (3-6 psi is enough for a leakage test, vent line removed and plugged at canister). Locate leaks with a stethoscope or CO meter.

^ In the rare case that a tank sucks in on a long drive or spits back when the filler cap is released after a short drive, suspect a crimp or blackage in the vent line between the canister inlet (check the inlet too) and filler housing. NOTE: From M80 the canister has a purge valve at the outlet. Basically, this is a non-return valve that opens at the slightest engine vacuum. This valve cannot block the system or cause too high pressure (the canister is open at the bottom to draw in fresh air).

^ New car won't start? If the cold start injector isn't operating during cranking, check that the harness connector plug at the thermo-time switch is not wired backwards. If it is, reverse the green and yellow wires.




^ A constantly running A/C compressor with the new mid-M80 cycling clutch system (identifiable by the absence of the VIR unit near the air inlet plenum could be caused by improper location of the thermostat capillary tube in the evaporator core. Before making any other checks be sure the capillary tube is correctly installed as illustrated below. (A few of the early factory-installed units, around VIN 90801013500, may have this tube installed only part way through the core.