reamer Posted July 12, 2019 Share Posted July 12, 2019 I have noticed with my Factory AC equipped cab (ac not operatable right now) No matter where the slide handle on the AC dash control, (even in the "off" position) I get a considerable breeze on the floor, amount of flow is dictated by speed. I thought in the "off" position no breeze should be coming from the cowl. true? Thanks Link to comment Share on other sites More sharing options...
Dorsai Posted July 12, 2019 Share Posted July 12, 2019 Are your kick panel vents open perchance? Link to comment Share on other sites More sharing options...
grumpin Posted July 12, 2019 Share Posted July 12, 2019 Vacuum leak? Link to comment Share on other sites More sharing options...
reamer Posted July 12, 2019 Author Share Posted July 12, 2019 Vacuum leak? On This AC cab, there are metal "seal-off" plates at the right and left kick-panel vents…. The breeze is coming from under the center of the dash at the plastic vents.... Link to comment Share on other sites More sharing options...
1986F150Six Posted July 12, 2019 Share Posted July 12, 2019 On This AC cab, there are metal "seal-off" plates at the right and left kick-panel vents…. The breeze is coming from under the center of the dash at the plastic vents.... Are any firewall rubber grommets missing or torn? Link to comment Share on other sites More sharing options...
packagerjr Posted July 12, 2019 Share Posted July 12, 2019 It’s possible the tab on the vacuum switch that kills power to the blower motor is broken, making those contacts closed all the time. In this pic, the short tab is operated by the big ramp and that kills power to the blower motor speed switch. Applicable to my 1980 but likely very similar regardless of year. Is the breeze related to fan speed? Link to comment Share on other sites More sharing options...
Steve83 Posted July 12, 2019 Share Posted July 12, 2019 ...breeze on the floor, amount of flow is dictated by speed. I thought in the "off" position no breeze should be coming from the cowl. true?No. The HVAC system is designed failsafe - if the whole thing shuts down (or is turned to OFF), driving forward still ventilates the cab. It's specifically described in the owner's manual. The pressure of the air hitting the w/s pushes that breeze down through the wiper cowl, through the fresh/recirc door (which defaults to FRESH), through the evap., past the temperature blend door (wherever you have it mechanically set), and out the FLOOR & DEFROST registers (the default of the diverter doors). It exits the cab through the louvers in the lower rear of the doors, and then out the louvers under the latches, into the airstream along the sides of the body. Link to comment Share on other sites More sharing options...
81f100custom Posted July 13, 2019 Share Posted July 13, 2019 ...breeze on the floor, amount of flow is dictated by speed. I thought in the "off" position no breeze should be coming from the cowl. true?No. The HVAC system is designed failsafe - if the whole thing shuts down (or is turned to OFF), driving forward still ventilates the cab. It's specifically described in the owner's manual. The pressure of the air hitting the w/s pushes that breeze down through the wiper cowl, through the fresh/recirc door (which defaults to FRESH), through the evap., past the temperature blend door (wherever you have it mechanically set), and out the FLOOR & DEFROST registers (the default of the diverter doors). It exits the cab through the louvers in the lower rear of the doors, and then out the louvers under the latches, into the airstream along the sides of the body. I would have to disagree as mine has no air flow at all in the off position. Some of the chevys I have do operate as you describe in the off position they still have air flow when you drive down the road. If you look at this diagram I believe if I am seeing it right there will be no air flow driving down the road when in the off position. In the off position you will have vacuum on 7A and 7B which in return closes off the defrost ducts. You will not have vacuum on 6 which shuts off air to the instrument panel registers. You will have vacuum on the outside recirculate door which seals any air flow from the outside if the system seals properly. Also there will be no power on the system in the off position so no blower motor moving any air. If you loose vacuum or have no vacuum then yes the recirculate door will open and you will have flow as you drive down the road and force air in. I am assuming he has vacuum on the system. Link to comment Share on other sites More sharing options...
Steve83 Posted July 14, 2019 Share Posted July 14, 2019 I would have to disagree as mine has no air flow at all in the off position. Some of the chevys I have do operate as you describe in the off position they still have air flow when you drive down the road. If you look at this diagram I believe if I am seeing it right there will be no air flow driving down the road when in the off position. In the off position you will have vacuum on 7A and 7B which in return closes off the defrost ducts. You will not have vacuum on 6 which shuts off air to the instrument panel registers. You will have vacuum on the outside recirculate door which seals any air flow from the outside if the system seals properly. Also there will be no power on the system in the off position so no blower motor moving any air. If you loose vacuum or have no vacuum then yes the recirculate door will open and you will have flow as you drive down the road and force air in. I am assuming he has vacuum on the system. It looks like I must have remembered the GM function then - that shows the fresh air is blocked in OFF. So the original problem is likely the same UV-degraded white recirculate motor vacuum line that causes the A/C to switch to the defrost registers under hard acceleration (low vacuum): https://supermotors.net/getfile/767412/thumbnail/recircline.jpg Link to comment Share on other sites More sharing options...
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