1998 GMC Jimmy Blows hot air

STEVEBROWN1950

MEMBER
1998 GMC JIMMY
6 CYL
4WD
AUTOMATIC
150,000 MILES

GOOD
Heat works fine in the winter
BAD
can't stop hot air in the summer
DETAILS
> My car has automatic temperature control which is wonderful in the winter. The summer can be a different matter!
> This is a temperature problem. Extremely hot air comes through the vents and the faster I drive the more that comes in.
> Turning the fan to off doesn't help.
> Dealer said I needed two parts both of which were buried in the dash - cost would be in $1000 range.
> I experienced the very hot air once this spring. It might have been during a hot spell. It occurred to me that the system might reset itself after a cold night and I swore to myself not to touch the controls again if it did reset - which it has! I have the fan off, the temperature is 74 and the duct setting is on center vents.

1 Reply

FACTORYJACK

MECHANIC
4,159 POSTS

Was there a diagnostic trouble code associated with this dealer diagnosis? In certain circumstances the system can be driven to full heat. Looking for maybe a B0408, B0415, or B0416. If it was a temperature actuator that was determined faulty, the procedure does show the instrument panel requiring removal to replace. Most all of the diagnostics for automatic HVAC require a scan tool, with this the actuator can be overridden to see if it responds to temperature change requests. Often times it is the actuator, but internal problems in the HVAC distribution case can also be a cause. Overtravel of an air mix door would be one example.