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Here's a Hard one. I have an 89 non turbo 300zx with climate control. On occasion i hear like a metal door under the dash open or close. I also have a clicking sound that sound like vacume solenoids closing Over and over , 2 seconds or so apart. Not all the time , but often. I've checked all the obvious vacume lines , but see nothing. Any ideas? Also whats a good way to check for vacume leaks. KK
 

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Mine does something similar but at a slightly slower rate.
Since the unit does still work fairly well I have not pursued the sound.
Maybe one day I will try the built in diagnostic system to see if it finds anything.
I suspect that it may be worn Potentio-Balance Resistors (PBRs) and the control unit is hunting the air mix doors to find the correct resistance back from the PBR.
At least the Solenoid Valves (S/Vs ) and Double Solenoid Vacuum Valves (DSVVs) are easy to get at so at least it might be easy to determine which is is switching in time with the sound.

The hunting may also be a result of a small leak in the power servos or vacuum acuators. Either way, I doubt there is a simple fix.
The PBRs are not easy to get at, they are located between the firewall and the HVAC assembly, so the dash would have to come out and then the HVAC box.

A handheld vacuum pump, like a Mity-Vac, comes in very handy locate faults in vacuum systems.
I have also made a little electric vacuum supply using the vacuum pump and tank from a turbo Z31.
Ultimately, the information in the 60-odd FSM pages devoted to the climate control system is the most valuable tool.
 

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The clicking probably comes from the row of vacuum thingamabobs right next to the gas pedal...when it starts you can feel which one is cycling...you can take the whole row out and look for leaks or whatever.
 

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Discussion Starter #4
The clicking does come from the vacum whatevers but it seems like all of them pulsing together. Hard to tell. Possibly from further up the line. Thanks for the input guys. KKing
 
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