To all who replied.

 

Problem turned out to be a loose set screw in back of the pressure(altitude) controller.  Gear and static switches were wired out of the circuit so never would have stopped pressurization any way.  Once the controller travel was adjusted and set screw tightened we could close the valve, initiate a ½ psi differential at 1500msl and c ontroller set to 0.  Unit functioned flawlessly in flight to 220 and rapid descent (1500-1800 fps).

Thanks to all who responded.

Tim

 

 

Thanks Bob and everyone who responded.

I’ll post what I find out for everyone’s education.

Tim

 

 

Tim wrote:

Cabin won’t pressurize.  Visitor shopping for a 4P was sitting in cabin with a battery charger on the battery supposedly studying the cheltons but I suspect he was pushing every button and switch he could.  Now pressure valve won’t close.  I can hear the dump switch and gear handle switch both clicking in the valve but it doesn’t move up or down.  Removed the valve and checked for travel.  I can manually close it on the bench but it immediately opens again.  With pressurized air flowing in (vacume cleaner hooked up in reverse) I can depress the valve with my fingers and almost get it to seal but it immediately opens.  Is there another safety switch in the pitot system somewhere?  Any idea where?

I’d appreciate any advice.

Thanks,

Tim, N524JG,  LNC4P, Ser# 411

 

Tim,

Are you sure you by-passed the gear-down switch? That’s the most likely cause of “pressurization dump” when the gear is down.  You can test this by pulling the hydraulic pump circuit breaker; then  [CAREFULLY and COMPLETELY] bleeding down the hydraulic system with the flaps. (You can add a safety factor by putting a length of  2x2 wood in the nose gear scissors.) When the hydraulic pressure is zero, by-pass the gear down-lock solenoid and raise the gear handle. Then test the system again.  In my airplane (depends on how the system is wired, but this is “standard”), the switch that controls the down-lock also controls power to the pressure controller.  Could a wire have come off one side of this switch…it’s behind the left side of the center vertical console, just below the gear operating lever. Your report of “clicking” above would seem to have already validated this part of the system, but worth checking twice…) Sorry I don’t have another idea…

 

BE SURE TO GET THE GEAR HANDLE BACK DOWN BEFORE RESTORING POWER TO THE HYDRAULIC SYSTEM.

 

Bob