2001 Ram 1500 5.2L

Okie dokie... So over the winter I swapped the heater core and a/c evap. core.

Heater seemed to work great for the first few days, and then I noticed less air volume from the vents. Even with the setting for the fan on high, the volume from the vents is still low at best. I also noticed that when I accelerate, sometimes, the volume from the fan goes to ZERO. I can hear the fan blowing just fine, but the air volume will be nonexistent until I let off the gas, and the RPMs come back down...

One other weird air thing going on...Even with the fan setting set to "off", sometimes, the vents will blow air for a few seconds at a time when driving under normal, steady RPM conditions.

 

You have a vacuum leak somewhere in the heater control lines and/or switch. Engine vacuum is highest at part throttle/low RPM, which is why it will work better at an idle, or as you let off the gas as in coming to a stop.

 

Just hit the forum search for "wild vents". You've got a failed vacuum check valve or leaky lines, or both.

 

I will check on that thanks