Question about Heating & Cooling
If the heat vents are controlled by vacuum, the problem is most likely a lack of vacuum to the control panel, or possibly a bad control panel. These are usually designed to send all the air to the defroster if there isn't vacuum to the system. This is probably so you can keep the windshield clear so you can see to drive if there is a problem with the system.
The system gets its vacuum from engine manifold vacuum. This often comes from a manifold vacuum block mounted on the firewall in the engine compartment, or on the back of the engine close to the firewall. If you start the engine and listen for a vacuum leak (hissing noise) under the dash or under the hood near the back of the engine, you may find the leak. It might be a hose that fell off a fitting, a split hose, a broken fitting, or a leaking vacuum canister (these are often mounted under the hood on an inner fender, and are typically about the size of a quart jar, and may be molded plastic or a "tin can" that looks like a juice can with a vacuum hose connected to it). If you find a vacuum leak and fix it, that may solve the problem.
If your HVAC (Heating, Ventilation, and Air Conditioning) system is controlled by electric motors or actuators, rather than vacuum, you may have a problem with a sticking or defective motor or actuator. There are typically 4 or 5 of these that operate the doors in the ductwork to direct the airflow to the different zones, to control air flow through the heater core, and to switch to recirculate mode for AC.
Posted on Sep 15, 2009
a 6ya expert can help you resolve that issue over the phone in a minute or two.
best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
Posted on Jan 02, 2017
Tips for a great answer:
Aug 30, 2015 | GMC Cars & Trucks
Nov 10, 2013 | 2000 GMC Safari
Jan 27, 2011 | 2000 GMC Safari
Oct 25, 2010 | 2003 GMC Safari
Aug 12, 2010 | 2000 GMC Safari
Oct 05, 2009 | 2000 GMC Safari
Aug 01, 2009 | 2000 GMC Safari
Jun 14, 2009 | 2000 GMC Safari
Oct 20, 2017 | Heating & Cooling
249 people viewed this question
Usually answered in minutes!