HVAC vacuum diagrams

Tiny
TOM SZCZEPANIAK
  • MEMBER
  • 2000 FORD F-150
  • 4.2L
  • 6 CYL
  • 2WD
  • MANUAL
  • 137,000 MILES
The blend door actuator(s) has apparently stopped working. I get only intermittent air flow through the dash vents. How many of these actuators does my truck have?
Tuesday, September 5th, 2017 AT 8:05 AM

3 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,227 POSTS
Blend door controls the air temperature. Mode doors control where the air goes.
If you cannot select hot/cold it is the first one, If you cannot select floor/dash/defrost it is the second.

In the case of an F150 you have a total of four vacuum actuators. One controls the fresh air/recirculate, one controls temperature and two are mode control.

All can be tested with a hand held vacuum pump at the back of the control panel.
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Tuesday, April 20th, 2021 AT 9:35 AM
Tiny
TOM SZCZEPANIAK
  • MEMBER
  • 2 POSTS
I do notice air flow through the dash board defroster vents and air flow through the vents down near the gas pedal when the switch is set on defrost or floor/defrost.
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Tuesday, April 20th, 2021 AT 9:35 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,227 POSTS
That sounds like the panel/defrost door is not operating properly. It is on the top left of the image. Connector 6 red on the control head. It could be a bad vacuum line or bad control itself. As you say it is intermittent, I would bet it is a bad line to the control. Sometimes it gets vacuum and other times it does not.
The control should be visible if you look up at the heater box from under the drivers side of the dash. The line should be easy to spot as well.
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Tuesday, April 20th, 2021 AT 9:35 AM

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