Nissan Repair: climate control, vacuum hoses, vacuum leak

Question
I have a 1987 300zx my temperature control does not seem to be working properly when I change from vent to floor to defrost it does not seem change it stays on defrost. If I change from hot to warm it will stay hot and a few minutes latter it will become to cold. I did pick up a used control switch assembly however I did not see an improvement.

Answer
Brian,

You need to check the back of the control panel for the air and the vacuum hoses that connect to the blend door motor.  A hose could be loose or the panel could be defective and even a vacuum line from the engine into the firewall could be defective.  Check for the vacuum leak on the system, under the dash and where it feeds to the vacuum canister that comes form the engine.