72allblackcoupe

1972 cutlass supreme Mayday Mayday a/C will not blow out the vents. It only blows from the bottom. Someone told me it is my vacuum diaphragm. ..whatever that is...can someone help

mrolds69

It could be...my questions would be...have you been working under the dash? Did it ever work right? Have you been working under the hood? It could be as simple as a hose falling off. The vacuum diaphram behind the pass vent panel, if bad, can cause that symptom.

72allblackcoupe

Mechanic checked vacuum hose . That's what he said it is ...the vacuum diaphragm. ....do you know where or how can I get one

drop top olds

The link shows the different vacuum diaphragms for typical GM cars. My 71 used VD235905 yours may be different. This part is located at the passenger side "kick panel". Must remove the kick panel to expose it. Be careful when removing the diaphragm. The plastic is most likely very brittle and may disintegrate upon careless handling.



http://www.classicbuicks.com/A_C_Hea...diaphragm.html

joe_padavano

The most likely problem is that the main vacuum hose from the engine that provides the vacuum source to operate the flapper doors in the HVAC box has come loose or cracked and is leaking. The A/C flapper doors are all vacuum actuated, and if vacuum is lost the flapper doors default to the heater/defrost positions. Verify that you have the vacuum hoses correctly connected under the hood. If so, you will need to do some basic troubleshooting. Use the vacuum hose diagram in the Chassis Service Manual to trace the hoses and check for vacuum at each with a vacuum gauge. The problem could be as simple as a loose hose, or a bad selector switch in the control panel, or a bad vacuum actuator diaphragm on the HVAC box. The latter is somewhat unlikely.

rocketraider

Will it switch from floor to the defrost ducts? If it won't switch off the floor in any control position, a disconnected or dryrotted vacuum hose is the most likely culprit.

Trace the vacuum line from the engine intake manifold to the vacuum storage ball and then to where it enters the firewall. Also snoop around that vacuum ball and see if it holds vacuum. Those A/C diaphrams need only about 7" Hg of vacuum to move but a leak anywhere in the system can drop vacuum enough to where stuff won't operate.

If it does turn out to be a vacuum motor, you can count on major underdash disassembly to replace it. The mounting fasteners are invariably INSIDE the ductwork.