The reason I say climate control is that it affects everything from heater to vent to A/C.

It doesn't matter if I'm in town or on the interstate. When the engine is under load, the air switches to the defrost vents. It doesn't matter what setting I have it on, it still does it until I ease up on the gas pedal and then it blows air normally on whatever setting I have it on.

For example, I will be cruising at 75 MPH on the interstate with the cruise control on. If the road is flat or downhill, the A/C, heater, vent, etc. blows normally on whatever setting I have it on. However, when I start to go up even a slight incline, the gas pedal goes further down to maintain speed and the air immediately switches to the defrost vents and stays that way until the road is flat or downhill again and the cruise control eases up on the gas pedal. It happens with or without cruise, downshift or no downshift.

To make a long story short, if the engine is under increased load, the air blows only through the defrost vents until the engine load is decreased.

Any idea what might be causing this?

 

You have a vacuum leak. Do a search on here for wild vents. This is a common issue.

 

Oh okay, thanks. I didn't know it was that common.

 

quick question. related maybe...

setting the fan on the first setting nets me, well.... no airflow (maybe, and i stress maybe, a marginal wisp of air... maybe) but at all other settings the fan blows fine, no howling or any other abnormalities. anyone?

 

Very common, inspect all the hoses and check valves that are next to the intake, make sure the hoses going to the CAD on the front axle are all good, and least but not last, if you have cruise control, inspect the hoses for that. Under the battery tray is where to look.

 

didnt mean to threadjack! but tyvm, gunna go poke around on her before i head home.