I need to know where the a/c vacuum block gets its vacuum supply. I have a 92 ford bronco xlt 5.8 and the emissions system has been taken out. MY problem is i cant get the vent door to activate from defrost to vents. There is no vacuum coming in.
AC vaccum problem
- Thread starter redsox34
- Start date
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Seabronc
New member
The problem with people taking off the emissions system is that they genreally don't know what they are doing and assume that everything with a vacuum line is part of the emissions system. Over the years the reserve canister design has changed from a metal can that looks like a used coffey can to high impact plastic globe to a smooth boxy device. In your truck I believe the vacuum reserve canister is a fairly large black plastic box on the passenger side and has the check valve built into it. It should have a Red line from the vacuum tree and a black line from it going through the fire wall on the passenger side. From there it hooks to the control system. If there is a break any where in that path your system will be stuck in the "Defrost default position" for safety purposes.
The attached picture is from an 83 Bronco, but they all work the same;
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The attached picture is from an 83 Bronco, but they all work the same;
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Last edited by a moderator:
yo redsox,
"...In 92-96, The air handling system is designed to provide defrost when no vacuum is applied to any of the three air door vacuum motors. This is done to prevent a situation where defrost cannot be obtained due to a system vacuum leak. Instead, a leak in the vacuum control circuit will send all airflow to the defroster outlets. This condition may occur during acceleration (slow leak), may exist at all times (large leak) and may happen only when certain specific functions are selected, indicating a leak in that portion of the circuit. ..." from F-150, F-250, F-350, F-Super Duty and Bronco, F-Super Duty Motorhome Chassis Workshop Manual
Source: by Ford via
http://www.thedieselstop.com/faq/9497faq/maint/stj/stjc0021.htm
A/C Switches to Defrost in MAX Mode; "...If MAX A/C only blows out the defrost registers, or if it switches to defrost during hard acceleration, this vacuum line (to the recirculate motor) is the reason. The white plastic is far more susceptible to UV light than any other color, and the gap along the edge of the hood allows it to degrade..."
Source: by Steve
Vacuum Circuit, Floor Panel Door, Temperature Blend Door (Cable Controlled), Floor & Defrost Door etc. Diagrams in a 96 from Workshop Manual
Source: by Ford via thedieselstop
http://www.thedieselstop.com/faq/9497faq/maint/stj/stjc2009.htm
"...In 92-96, The air handling system is designed to provide defrost when no vacuum is applied to any of the three air door vacuum motors. This is done to prevent a situation where defrost cannot be obtained due to a system vacuum leak. Instead, a leak in the vacuum control circuit will send all airflow to the defroster outlets. This condition may occur during acceleration (slow leak), may exist at all times (large leak) and may happen only when certain specific functions are selected, indicating a leak in that portion of the circuit. ..." from F-150, F-250, F-350, F-Super Duty and Bronco, F-Super Duty Motorhome Chassis Workshop Manual
Source: by Ford via
http://www.thedieselstop.com/faq/9497faq/maint/stj/stjc0021.htm
A/C Switches to Defrost in MAX Mode; "...If MAX A/C only blows out the defrost registers, or if it switches to defrost during hard acceleration, this vacuum line (to the recirculate motor) is the reason. The white plastic is far more susceptible to UV light than any other color, and the gap along the edge of the hood allows it to degrade..."
Source: by Steve
Vacuum Circuit, Floor Panel Door, Temperature Blend Door (Cable Controlled), Floor & Defrost Door etc. Diagrams in a 96 from Workshop Manual
Source: by Ford via thedieselstop
http://www.thedieselstop.com/faq/9497faq/maint/stj/stjc2009.htm
Seabronc
New member
The picture shared by miesk5 show you the color codes for your control. I think that will answer your question.
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