Defrost and Demist System

A/C System Functional Test - Defrost and Demist Testing

1. Set the TEMPERATURE SELECTOR to 85.

2. Sec MODE CONTROL to DEFROST.

3. Close END OF DASH outlets.

4. Start engine and run at 1500 rpm for 7 minutes.

5. During the running period, measure air flow from screen outlets.

The velocity should be 1550 f.p.m.

6. Also during running period turn MODE CONTROL to HIGH and open END

DASH outlets. Using screen outlets and end of dash outlets, measure air velocity.

7. Should be 500 f.p.m. screen - 850 f.p.m. end of dash outlets minimum.

8. At the end of 7 minutes running period and the engine water temperature gauge is at normal, the following minimum screen outlet temperature should be obtained:

PLENUM INLET °C

10
12
14
16
18
20
22
24

SCREEN OUTLET °C

54
55
55.5
56.5
57
58
58.5
59.5

9. If the above minimum requirements are met, it can be assumed that:

(a) The thermostats are opening correctly.

(b) Water valve is opening fully.

(c) The flaps and linkage are correctly adjusted for the heating mode.

(d) The fans give adequate air flow at maximum speed.

10. If the above criteria are not met, check the following:

11. If water temperature will not reach normal in 7 minutes, check thermostat(s).

12. Water temperature is normal but the air outlet temperature remains low, check that vacuum to heater water valve is at least 8-1/2 inches

(Hg). If vacuum is sufficient, replace valve. However, if vacuum is low, check supply through water valve actuator, switch and supply pipe for a pinched condition.

13. if air velocity is low, check that appropriate flaps are fully closed adjust linkage if necessary. Excessive air flow may be caused by demist control flap sticking open.

14. If after checking flaps, air flow is still low, check blower motors for full voltage at maximum speed and that the motors are wired for correct rotation.