1990 C350, AC vent issues
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Post Fiend
Joined: Nov 2001
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From: Coutts Canada
1990 C350, AC vent issues
Alrigty I have a quick question in regards to my 1990 460 auto 4wd 4 door one ton bronco, it's about the AC and the vents.
Basic problem is that it doesn't blow out of the dash vents when you have them selected, it either blows out on the floor vents or the defrost vents on he windshield. I've checked the vacuum line to the motor that controls the flapper thingy that directs air and it's free of holes/leaks, and the vacuum actuator still works. Also the vents will work temporarily when the engine is in a high vacuum state (ie when letting off the throttle after a high load).
I'm not sure where to go from here to get the AC to work properly and blow out the vents, any ideas on where to look next?
Could their be a vacuum leak elsewhere in the sytem causing this (like on the brake boosters?)
Thanks.
Basic problem is that it doesn't blow out of the dash vents when you have them selected, it either blows out on the floor vents or the defrost vents on he windshield. I've checked the vacuum line to the motor that controls the flapper thingy that directs air and it's free of holes/leaks, and the vacuum actuator still works. Also the vents will work temporarily when the engine is in a high vacuum state (ie when letting off the throttle after a high load).
I'm not sure where to go from here to get the AC to work properly and blow out the vents, any ideas on where to look next?
Could their be a vacuum leak elsewhere in the sytem causing this (like on the brake boosters?)
Thanks.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
There is another vacuum reservoir for the HVAC system too. Yours maybe a metal coffee can looking device or a big plastic dual reservoir located on the passenger side fender. If it is metal it tends to corrode on the bottom side.
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That is the vacuum reservoir for the EGR. The reservoir for the HVAC is glued to the evaporator housing (and usually fails after so many miles).
Fleet Owner
Joined: Oct 2005
Posts: 20,789
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From: Kentucky
My 1992 F350 had a smaller "tuna can" sized reservoir behind the driver side headlight for the vacuum controlled cruise control. It was rusted out. The cruise acted funky under load, sometimes dropping out completely. I also noticed the HVAC would also start to waver a bit, but not drop out like the OPs unless I was going up a hill.
A large vacuum leak such as these pesky metal reservoirs will affect any of these vacuum controlled systems.
Thanks again for catching my mistake of pointing to the wrong one and referring to it as the HVAC reservoir!
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You are correct kind sir. I did forget about that little plastic reservoir. But we have found the one I referred to will indeed no longer act as a reservoir and become a huge vacuum leak which in turn can affect the HVAC system.
My 1992 F350 had a smaller "tuna can" sized reservoir behind the driver side headlight for the vacuum controlled cruise control. It was rusted out. The cruise acted funky under load, sometimes dropping out completely. I also noticed the HVAC would also start to waver a bit, but not drop out like the OPs unless I was going up a hill.
A large vacuum leak such as these pesky metal reservoirs will affect any of these vacuum controlled systems.
Thanks again for catching my mistake of pointing to the wrong one and referring to it as the HVAC reservoir!
My 1992 F350 had a smaller "tuna can" sized reservoir behind the driver side headlight for the vacuum controlled cruise control. It was rusted out. The cruise acted funky under load, sometimes dropping out completely. I also noticed the HVAC would also start to waver a bit, but not drop out like the OPs unless I was going up a hill.
A large vacuum leak such as these pesky metal reservoirs will affect any of these vacuum controlled systems.
Thanks again for catching my mistake of pointing to the wrong one and referring to it as the HVAC reservoir!
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