QuestionThe AC and heating system works fine from the standpoint of the controls. My concern is low air flow in heating or cooling. Do I have a damper problem? Is there a filter or some inlet blocked. The fan is making all sorts of noise but air flow is low even on high.
AnswerHi David,
If the fan gets progressively louder, but the airflow stays the same, then you probably have a blockage. If the fan motor seems to have one loud speed, or you hear a vibration, then it's possible that either the squirrel cage is loose on the fan shaft, or there is something wrong with the motor. More than one rodent has found a cozy bed around that area;)
Most likely, the evaporator is being obstructed. On these vehicles (actually, C and H bodies), the evaporator often collected dust and debris from the fresh air vent. Commonly, the evaporator itself had a slight leak, and the oil that covered the outer core served as a perfect magnet for this crap.
If the A/C is still cooling, then its possible to just clean the front of the evaporator off with a light spray solvent (really, a non-corrosive chemical) or compressed air. In the shop, we erroneously used brake cleaner, but compressed air can sometimes do the trick. If you're lucky, the dirt will peel off like a fur coat. To access this, you can remove the Blower Motor Resistor Block (or Module), on the firewall-mounted HVAC case, in the engine compartment -- note that the hole is not big, but it's enough to shine a light in and stick an air nozzle down into. On some of the tougher ones (that were leaking as well), it was necessary to remove the HVAC case and replace the evaporator.
Good luck!
