1979 Models

Check ignition timing at idle and adjust if necessary. Disconnect vacuum hose from distributor sub-diaphragm. Timing should advance 10 degrees toward TDC on all models. Reconnect vacuum hose.
Disconnect vacuum hose from Black side of delay valve and pinch hose. Ignition timing should remain at initial timing position for more than one minute. Reconnect hose and stop engine.
Disconnect top hoses from HAC valve and blow into hoses one at a time. Check that air flows into carburetor. If not, check hoses and carburetor fittings for obstructions.
Remove check valve from system. Blow into White side of check valve. Air should flow out. Blow into Black side of check valve. No air should flow. If valve does not operate as indicated, replace check valve.

Fig 1: 1977 HAC System Test (2T-C Engine Above 4000 Ft.)

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: 1977 HAC System Test (20R Engine Above 4000 Ft.)

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 3: 1977 HAC System Test (2F Engine Above 4000 Ft.)

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 4: 1977 HAC System Test (2T-C, 20R & 2F Engines Below 4000 Ft.)

Fig 5: 1979 High Altitude Compensation (4M Engine)

Fig 6: 1979 High Altitude Compensation (2F Engine)