Hello,

Identify the system...auto air, or manual?

Usually default failure of system goes to full heat (actually mandated)...

Unrelated prior post of battery/screen issue correct?

Could you identify heater/ac control panel>(HVAC module)(where you push the buttons).

Most heater valve probs actually unrelated to this problem, only if you have no or limited heat.

The most prevalent items in those trucks were the actual failure of the control/user interface module.

I am out for a while running something called a farm...:)

I'll check back tonight.

Good Luck,

CF

PS: control panel general types...

(late 98 HVAC module (full).png)

(88 up Climate Module (full).png)

late 98 HVAC module (full).png (21KB - 2 downloads)

88 up Climate Module (full).png (34KB - 1 downloads)