Heater-A/C Control Assembly Vacuum Test

Adjusting Test Bleed Valve:

Start vacuum pump Tool 0-4081, or C-4289, and connect the vacuum test set Tool 0-3707. Adjust bleed valve on test set to obtain a vacuum reading of exactly 8 inches of mercury (-27 kPag) with a finger blocking the prod on end of test hose.

It is essential that the bleed valve be adjusted so the vacuum gauge pointer will return to exactly 8 inches (-27 kPag) when the prod is covered by a finger. Otherwise a false reading will be obtained when the control circuit is tested.

Alternately release and reblock the hose prod several times. Make sure the bleed valve is adjusted so the vacuum gauge pointer returns to exactly 8 inches of vacuum (-27 kpag) when the prod is covered with a finger.

Disconnect engine vacuum source hose in the engine compartment and insert vacuum tester hose prod into source hose leading to control switch. Place vacuum gauge on the cowl so it can be observed from the driver's position as control is operated.

Start the test by setting the control selector on FLOOR position. Vacuum tester gauge needle will drop until the actuator has operated, and should then return to 7-1/4 to 8 inches (-25 to -27 kPag) Then change mode selector to DEFROST, BI-LEVEL, PANEL, and if so equipped RECIRC (allow 15 seconds in each mode setting to assure full operating cycle).

Allowing time for actuators to operate after each selection, and for the vacuum to stabilize. Note the vacuum drop below 8 inches (-27 kPag) after each operation. The maximum allowable vacuum drop below 8 inches (-27 kPag) after each operation is 3/4 inch (-3 kPag).

If the vacuum drop is more than 3/4 inch (-3 kPag), first recheck the tester for reading exactly 8 inches (-27 kPag). If correct, inspect the 7-port hose connector plug for leaks. This plug must be positioned all the way onto the 7-port receiver pigtail at the control.

CAUTION: Do not use lubricant on the switch ports or in the holes in the plug, as lubricant will damage the vacuum valve in the switch. If it is difficult to properly position the connector plug all the way on the switch ports, put a drop or two of clean water in the holes of the connector plug. This will allow the plug to slide completely on the switch ports.

Vacuum Tube Assembly Test:

If vacuum drop is now within limits, proceed with the overall performance test. If vacuum drop is still in excess of 3/4 inch (-3 kPag), remove 7-port connector from switch and seal port No. 6 with a finger to check source hose. Then remove prod from source line and insert it alternately into each connector port except No. 6.

Note amount of vacuum drop below 8 inches (-27 kPag) after each actuator has operated. If vacuum test gauge comes back to 8 inches (-27 kPag) at each of the 7 ports, the hoses and actuators are not leaking. The control switch is faulty and must be replaced. If excessive vacuum drop shows up at one or more ports in connector block, isolate faulty hose or actuator.

Inspect hose connections to the actuator involved. Then test whether actuator or hose is at fault; use the test hose on the actuator involved.

A leak in a hose may be detected with vacuum test set by running the fingers along the hose and watching vacuum gauge reading. The line can be repaired by cutting out the "leak" and inserting the line into a 1/8 inch (3 mm) inside diameter rubber hose.

A vacuum drop in excess of 3/4 inch (-3 kPag) below the 8 inches (-27 kPag) needed in this test will not interfere with the engine operation, other than perhaps to cause a rough idle. It can, however, interfere with the proper operation of the air-conditioning and heating controls at high speeds and during acceleration.