Functional Check. GMC Truck GMC K Sierra

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC K Sierra - 4WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 Functional Check

As an aid in determining whether or not the following are operating properly, refer to the System Performance table:

•	The air conditioning (A/C)

•	Electrical

•

Air

•	The refrigeration systems

The operation of the air conditioning (A/C) blower at all 5 speeds, in any position except the OFF position, and the engagement of the compressor clutch indicate that the electrical circuits are functioning properly.
The operation of the A/C control selector and the distribution of air from the designated outlets indicates proper functioning.


(1)	Upper Mode
(2)	Bi-Level Mode
(3)	Lower Mode
(4)	Defog Mode
(5)	Defrost Mode

System Performance

Control Settings			System Response
Mode Control	Temp Control	Fan Switch	Blower Speed	Heater Outlets	A/C Outlets	Defroster Outlets	See Remarks
--	Cold	--	Off	No Air Flow	No Air Flow	No Air Flow	--
Upper	Cold	Lo	Low	No Air Flow	Air Flow	No Air Flow	A,C,D
Upper	Cold	Low to Hi	Low to High	No Air Flow	Air Flow	No Air Flow	A,B,C,D
Upper	Cold	Hi	High	No Air Flow	Air Flow	No Air Flow	A,D
Bi-Level	Cold	Hi	High	Air Flow	Air Flow	No Air Flow	A,D
Lower	Hot	Hi	High	Air Flow	No Air Flow	Min Air Flow	A,D
Defog	Hot	Hi	High	Air Flow	No Air Flow	Air Flow	A,D
Defrost	Hot	Hi	High	Min Air Flow	No Air Flow	Air Flow	A,D
A = Engagement of the detent must be felt in each mode. B = Noticeable blower speed increase must occur from low to Med 1, Med 2, Med 3, and high. C = Listen for changes of air noise from recirculation door closing. D = Some air bleed will occur through defroster and side window defogger vents in heater mode.

Cold and Hot Air Test

With the mode knob in DEFROST, the temp knob in HOT, and the fan switch in HIGH, temperature from the defroster outlet should be above the temperature outside of the vehicle.