Defrost doesn’t blow air to the windshield vents

ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#16224 Closed 1990 Cadillac Brougham D'Elegance 5.7L public

Hello Sparky,

I came across your site and I love the work you do. I’m so thankful to find that you also take questions and help individuals with their issues.

I have a 1990 Cadillac Brougham D’Elegance 5.7L RWD 4 Door Sedan. I have Automatic climate control. I recently replaced the MAP sensor, heater core, windshield wiper motor, full tune up, air conditioner recharge, etc. The AC works great, front vents blow nice, car cools fine. It’s starting to get cold in NYC so now it’s heater time. I tried turning on my front windshield defroster but no air at all comes out of the windshield vents. I get heat from the floor vents but nothing out of the side vents or the defroster when I put it on 90ºf or on defrost. I can’t find a mechanic in NYC that knows anything about this car (or wants to try to work on it as time is money and they don’t want to waste their time) so I’ve turned to the internet for help.

I heard that it can be a vacuum leak somewhere but not sure how to trace it. I found a random hose off a T connection near the black canister at the driver’s side front behind the headlight. I don’t know where it goes and it has vacuum on it. I’m trying to find where it connects to. I’m not sure what to check or replace to get this working. I just got the car on the road in the past 4 months and it’s been sitting for about 8 years. It runs like a dream and everything works but the radio and the defroster. Any help you can give me would be greatly appreciated. Let me know if there’s anything else you need from me.

Oh and here’s a link to my google drive with photos of the engine compartment.

Thanks again,

Marc 917-543-9749


The most likely problem would be a vacuum issue. Finding where that hose attaches would be the first step. There are three possibilities as I see it.

1. It attaches to what appears to be a hard plastic line that is located at the edge of the fender near the end of the cruise control servo. The cruise servo is the odd shaped part that has a cable on it that attaches to the throttle linkage.

2. It attaches to a fitting under the cruise control servo and will be found near where the larger attached vacuum hose is located.

3. It attaches to the vapor canister. The vapor canister is the black plastic container that mounts vertically in the inner fender panel.

Thanks so much for your response. I definitely have a vacuum issue as I just found out my Cruise Control isn’t working and neither is my defroster. I have to try and find out how to trace that leak or broken hose. I will check it out and get back to you.


You have likely already found half of the leak with that loose vacuum hose you were holding. The easy thing to do is to start the engine and check to see if that loose hose has vacuum on it or not. If it does you simply need to locate what it attaches to. If it does not have vacuum in it then listen carefully for the hissing sound of the vacuum source leaking.

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