Disclaimer: These instructions are
for an early (e.g. '63-'65) Riviera.
The '64 Riviera A/C system used two
identical dual-stage vacuum diaphragms. They are called "dual-stage"
diaphragms because there are two "circuits" in each diaphragm.
Vacuum applied to either port individually will pull the shaft in
halfway. Vacuum applied to both ports will pull the shaft in all the
way. You can test the diaphragm by putting a piece of hose on each
nipple, sucking on it, and seeing if it holds vacuum. New diaphragms
are available from
Old Air Products.
The upper diaphragm is mounted on top
of the heater duct. It opens and closes the heater air door
(not the heater temperature door, which is controlled by a cable).
The lower diaphragm is mounted on the bottom of the blower housing.
It opens and closes the recirculated air door.