1967 Max Air Conditioning blows out of floor vents

nickmobile67

New Member
Jan 7, 2004
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I have a '67 Mustang with factory air conditioning. On regular ac the air blows out of the dash vents like it should, if I switch it to max ac it blows cold air out of the floor vents. The vacuum lines have all been replaced and appear to be run correctly. I checked the vacuum lines on the back of the control panel and they are all on there and tight. Any common things to look for? Thanks!
 
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jakohle

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Jul 7, 2020
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I assumed you checked vacuum canister on the passenger side under the hood hinge and you have vacuum there? If not check that first. If that has vacuum.

Then sitting in the driver seat reach your right hand under the dash behind the ignition switch on the driver side of blower motor assembly, and there is a vacuum line attached to a vacuum motor. With the car running and MAX A/C enable see if you have vacuum at that vacuum motor? If you have vacuum reach back under the dash and pull the arm on the top side of the vacuum motor down. air should be blowing out of the dash. Stick your finger over the vacuum port on the vacuum motor. Then let go of the arm on top of the vacuum motor. If the arm goes up when you are plugging the vacuum on that vacuum motor the motor is bad. You can pull the ash try, and cigarette lighter to make things easier to get to if you want. Replacing that vacuum motor on the car is hard because you have to drill the rivets out. However, that blower motor assemble only comes out if you remove the evaporator and heater core assemble on the passenger side. If you do that you have to charger A/C and all again. So, I would try replacing on the car first. Below are some picture of the blower motor assembly. The blue arrow points to the vacuum motor in question. This one is a replacement vacuum motor on my assembly so you can see it is bolted on. The factory originals are riveted.
 

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jakohle

New Member
Jul 7, 2020
6
0
1
41
Mesa Arizona
I assumed you checked vacuum canister on the passenger side under the hood hinge and you have vacuum there? If not check that first. If that has vacuum.

Then sitting in the driver seat reach your right hand under the dash behind the ignition switch on the driver side of blower motor assembly, and there is a vacuum line attached to a vacuum motor. With the car running and MAX A/C enable see if you have vacuum at that vacuum motor? If you have vacuum reach back under the dash and pull the arm on the top side of the vacuum motor down. air should be blowing out of the dash. Stick your finger over the vacuum port on the vacuum motor. Then let go of the arm on top of the vacuum motor. If the arm goes up when you are plugging the vacuum on that vacuum motor the motor is bad. See below paragraph. If the vacuum motor is good then the switch is bad and vacuum is not being directed to the vacuum motor on MAX AC. (This is most likely the case based on what you are describing.)


You can pull the ash try, and cigarette lighter to make things easier to get to if you want. Replacing that vacuum motor on the car is hard because you have to drill the rivets out. However, that blower motor assemble only comes out if you remove the evaporator and heater core assemble on the passenger side. If you do that you have to charger A/C and all again. So, I would try replacing on the car first. Below are some picture of the blower motor assembly. The blue arrow points to the vacuum motor in question. This one is a replacement vacuum motor on my assembly so you can see it is bolted on. The factory originals are riveted.
 
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