Jeep Garage  - Jeep Forum banner
1 - 2 of 2 Posts

·
Registered
1997 Jeep Grand Cher
Joined
·
1 Posts
Discussion Starter · #1 ·
Hi Everyone :)

My Jeep has the non-automatic climate control system. When the 318ci engine is under load (ie: passing on the highway), the climate control air will suddenly start to blow by the windshield (even though I hadn’t selected the defrost modes). To make matters worse, the air temperature is stone cold.

I’ll try to explain in more detail with a typical scenario: Say I’m highway driving in winter time, and the outside temperature is cold. In this example, I have the blower motor set to HIGH, the temperature control knob turned to HOT, and the mode selector dial set to PANEL (which means that the air is supposed to flow through the outlets located in the instrument panel). Because it’s a dry winter day, the A/C button is not activated. Everything will work as it should, until the gas-engine experience an extra load. (Note: This extra load can come from climbing a steep hill at highway speed, or passing another vehicle). When the gas-engine is under this extra-load, unheated air will be suddenly directed to the windshield (as if I had physically selected the DEFROST setting on the mode selector dial) and no heated air will flow through the panel outlets at all. You can actually hear the air dampers within the dashboard moving when this is happening. However, everything will revert to status quo once the engine is no longer under stress.

The Jeep has been running fine, and the gas mileage is good (for a V8 :)

If anyone can help me solve this conundrum, it would be greatly appreciated.
 

·
Premium Member
SRT8
Joined
·
2,623 Posts
Hi Everyone :)

My Jeep has the non-automatic climate control system. When the 318ci engine is under load (ie: passing on the highway), the climate control air will suddenly start to blow by the windshield (even though I hadn’t selected the defrost modes). To make matters worse, the air temperature is stone cold.

I’ll try to explain in more detail with a typical scenario: Say I’m highway driving in winter time, and the outside temperature is cold. In this example, I have the blower motor set to HIGH, the temperature control knob turned to HOT, and the mode selector dial set to PANEL (which means that the air is supposed to flow through the outlets located in the instrument panel). Because it’s a dry winter day, the A/C button is not activated. Everything will work as it should, until the gas-engine experience an extra load. (Note: This extra load can come from climbing a steep hill at highway speed, or passing another vehicle). When the gas-engine is under this extra-load, unheated air will be suddenly directed to the windshield (as if I had physically selected the DEFROST setting on the mode selector dial) and no heated air will flow through the panel outlets at all. You can actually hear the air dampers within the dashboard moving when this is happening. However, everything will revert to status quo once the engine is no longer under stress.

The Jeep has been running fine, and the gas mileage is good (for a V8 :)

If anyone can help me solve this conundrum, it would be greatly appreciated.
You have a Vacuum leak, the HVAC system defaults to Defrost mode when the Vacuum is lost.

I bet your Cruise control also stops. there is a Vacuum canister under the Battery tray, it cracks etc.

Google around there's Plenty of ZJ forums on it.

Fixed vacuum leak now HVAC controls work & more benefits! 93 ZJ - North American Grand Cherokee Association
 
1 - 2 of 2 Posts
Top