AC not blowing out of vents

[dpmeloan]

Air is not coming out of the dash vents when AC is turned on, only comes out of floor vent. Fan is working on all speeds, compressor engages. Car was parked in museum for 9 months and worked prior to that. Suggestions on what the issue might be would be appreciated. Car is a 1961 Cadillac Coupe deVille. Thanks!

[79 Eldorado]

Doug,
A '61 is too early for me but either your mode selection isn't working, mode door is stuck, or possibly a piece of duct work became disconnected. Was Cadillac already using vacuum for control in '61?

One other interesting point an engineer, who did a lot of the HVAC work on Cadillac, told me once that the GM systems were designed to be fail safe to go to defrost mode. I can tell you that's absolutely not what happens in one of my '79 E Bodies. Loss of vacuum and everything goes to heater mode exactly as you described but that was almost 20 years later.

Scott

[quadfins]

Default position in a '61, with all vauccum actuated sytems off is for the outside fresh air path to be closed, and air circulation (which there still could be, if the fan is running) to be directed through the heater system. Inside the heater box is a diverter arm that directs heated air either to the floor openings or the defrost outlets. This arm is moved by a Bowden cable, operated by the heater/defrost control. So by default, with the fan on, air goes through the heater core, and heated air can go to either the floor ducts or the defrost. Try moving the defrost lever and see if airflow changes.

One way or another, this would NOT go through the dash vents.

AC-equipped cars have a larger air diverter box mounted on the engine side of the cowl. This box has several vacuum-operated diverter doors within. The Blue vacuum line operates the actuator that directs air away from the heater path, and into the path that blows through the AC evaporator, then out the dash vents. That path opens when your AC lever is moved to Vent. When you move the lever to AC, the only change is that it actuates the compressor.

If you turn on the heater at the same time, vacuum is cut off from the blue line, but stays on the purple line. This moves the director door to a half-way position, with half of the air going through the evaporator and dash vents, and the other half into the heater core and floor/defrost path.

So, with that convoluted explanation, it sounds like the problem is with the blue line or actuator. the vacuum line may be disconnected, broken, or leaky, or the actuator may be faulty. These things happen when we get to be 60 years old, or so.

The easiest way to test is to get an extra length of vacuum line, connect it to the "blue" actuator and apply vacuum - either through a hand-operated vacuum pump, or just suck on it (I am not trying to be rude, here...). Have a helper sit in the car and feel for air flow at the dash vents. The engine does not need to be running - just turn the ignition switch to the accessory position so the fan will run. Turn the fan on High (by default it will draw air through the interior cabin). You should feel air coming out the floor vents. Move the defrost lever - air should now come out of the defrost. Then... conduct the "suck-test", and see if you get any air out of the dash vents. If not, you can assume the fault lies somewhere in that "blue line".

If you like, give me a call - I am in the directrory - and I can "walk you through it". It would give me an excuse to get out of mowing the lawn, and I would much rather work on/talk cars today.

Attached is the vacuum diagram

Jim

[cadillacmike68]

1961 was before Climate control, which started in 1964. 1964-66 still used a cable to control part of the system operation, but by 1967-68 and onward, I can verify that the fail safe forced blower turned on (by jumping the master switch) Does go into defrost mode as far as air flow is concerned. Cooled air is also the default (no vacuum to the big power servo "donut"). The vacuum and controls have to pull off the mode door to get the system to come out the dash vents.

So if you have a bad vacuum leak and jump the master switch, the fan will blow (at least on LO) and if the transducer circuit goes bad (electrical or vacuum) you will get cooled dehumidified air which will keep the windshield clear. I have experienced this enough times in the past.

[dpmeloan]

Thanks everyone for your excellent input and suggestions.  The culprit ended up being a really simple, yet elusive, fix.  The vacuum hose leading from the AC/Heating control valve had come disconnected at the manifold, so there was no vacuum going to the switch. Found this after I noticed the emergency brake pedal was not disengaging when put into gear.  Glad it was this simple!  Thanks again everyone!  Doug

[Ginabauta]

Thank you very much for this topic, you gave me an idea of how I can solve my problem. The users above gave very clearly stated possible problems and, most importantly, ways to solve them. I always tried to repair any damage independently, and in the rarest cases, I turned to car service stations. They usually ask for a job that lasts only 10 minutes a huge amount of money, trying to justify this with many terminologies. Those who do not understand cars may believe it, but you can't deceive me. I'm interested in what you fill the compressor with. Personally, I use the R22 from a familiar air conditioner servicing company.

[DeirdreGraham]

Speaking of compressor failure. Even with proper operation, the compressor can wear out physically and one day stop starting.  If you have skills in working with electrical devices, you can get to the compressor yourself, find the supply wires, remove the terminals and measure the resistance between the terminals. Before starting work, do not forget to disconnect from the power grid. Thus, the resistance between the primary winding lead and the starting winding lead should be equal to the sum of the resistances between the windings and the third lead. Do not take up the repair yourself if you do not have enough experience. Call https://www.marvellous.sg/aircon-leaking-water/- so that you will get a guaranteed quality repair.