When I turn the defrost on in my truck the fan blows hard but the air is not directed to the defrost vents. Is there a solenoid in the vent system which diverts the air up.. and where is it ? When I turn the heat regulator to cool air the air will blow steady through the defrost vents
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GMC 2000 Sonoma Heater vents?
- Thread starter mdsaco
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epiphaknee
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Do you have a 4.3L, 4WD, truck? Do you have any reddish colored liquid or substance in your ashtray? Just above the ashtray? If so, consider the vacuum switch on the transfer case and consider that your vacuum lines have filled with transmission fluid - a bad day had by all. Replace the vacuum switch (about $15.00) and the compromised vacuum lines. Clogged vacuum lines creates vacuum "problems."
The vent doors are controlled by vacuum which is directed to the vent doors by the AC/Heater Control Mode Switch. The temperature mode switch, electronically controls the temp blend door at the firewall on the passenger side of the vehicle.
Your defrost door does open but only when the AC/Heater Mode Control is in the AC position. Hence, I would start at the AC/Heater Control Mode Switch. Is it hissing? This would indicate that vacuum is being lost at the switch. If hissing try to find out where it is hissing. If at the switch, then the switch is probably bad. If elsewhere, then one of the vacuum hoses may be leaking or pinched.
The vent doors are controlled by vacuum which is directed to the vent doors by the AC/Heater Control Mode Switch. The temperature mode switch, electronically controls the temp blend door at the firewall on the passenger side of the vehicle.
Your defrost door does open but only when the AC/Heater Mode Control is in the AC position. Hence, I would start at the AC/Heater Control Mode Switch. Is it hissing? This would indicate that vacuum is being lost at the switch. If hissing try to find out where it is hissing. If at the switch, then the switch is probably bad. If elsewhere, then one of the vacuum hoses may be leaking or pinched.