Question about 2000 GMC Envoy
Not an easy fix - sounds like either a heater/AC plenum control diaphragm started leaking, or a vacuum hose to one of them has popped off at the actuator or at the heater control, or the vacuum line developed a leak somewhere between an actuator and the heater control or the engine. You can try to pin down by checking airflow out of the defroster, ac and heater vents - if airflow is normal in each position, the problem is probably the heat/cool control actuator, the line from it to the heater control, or the heater control itself.
Posted on Nov 25, 2014
There may be a small hole or cut in a vacum line or possibly just loose. Also make sure the air filter box and the big hose to it are secure and clamps etc are tight. Pulleys and belts can make a high pitch sound also.
Posted on Mar 22, 2009
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