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From: Robert R Pastusek <rpastusek@htii.com>
To: Lancair Mailing List <lml@lancaironline.net>
Subject: RE: [LML] IV P door seal 
Thread-Topic: [LML] IV P door seal 
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Date: Wed, 18 Jun 2014 19:27:02 +0000
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BOB C WROTE:
After turning on the Master switch on a 40F morning at S Lake Tahoe (6000' =
+), the door seal motor started on its own accord. Numerous attempts to cyc=
le the Master, the motor CB, and the motor switch, provided no help. So I f=
lew back to AZ unpressurized. After landing, the motor operated normally. A=
ny ideas?
Thanks,
Bob C
338L

Bob,

The door seal system in the IV-P's and ES-P's has been installed and wired =
in several different ways by builders; some in accordance with the build ma=
nual that was changed over time, and some by "original" thinking. All I hav=
e seen have one function in common: The door seal pump is wired in series w=
ith a pressure switch that senses pressure inside the seal and operates the=
 pump any time  the circuit has power applied to it and the pressure is bel=
ow the pressure switch setting (it's adjustable, if the "standard" Lancair-=
provided part was used). So, master on and seal pressure low: Power to the =
pump. As soon as the pressure gets to the pre-set level, the switch turns t=
he pump off automatically. The pump is powerful enough to "explode" the sea=
l if it's inflated with the door open and the pressure switch set high enou=
gh, so some caution when testing/working on this system--you can quickly cr=
eate more trouble for yourself...

But back to the basic issue: If the pump runs when power is applied, the in=
-line pressure switch thinks the seal internal air pressure is too low. The=
 fact that it seems to be working normally now would cause me to suspect th=
e electrical pressure switch itself. The switches supplied by Lancair were =
"automotive quality," and while "good enough" for non-critical uses, are su=
bject to failure. ...and they are relatively in-expensive to replace. (BTW,=
 a spare pressure switch for the door seal, and also one for the hydraulic =
pump are in my in-aircraft tool/parts bag.) The fact that the pump ran cont=
inuously for an extended period could indicate a leak in the door seal--per=
haps only when under pressure-- or a blocked inlet port to the pump--keepin=
g it from drawing air to compress. The third component that might have caus=
ed what  you report is the (mechanical) door pressurization switch. For mos=
t installations I've seen, the pressure pump output is connected directly t=
o this switch, and the switch mechanically ports the pressurized air to the=
 door seal in one position, and blocks it completely in the "door seal off"=
 position. (In the "off" position, the pump will run for a short period whe=
n power is applied, until the line pressure to the switch reaches the press=
ure set point; then turn off.  This switch also vents the door seal in the =
"off" position, allowing it to deflate. If the mechanical switch is stuck i=
n an intermediate position, or if the internal shuttle "hangs up," it can p=
ort pressurized air from the pump directly out the vent. A less likely fail=
ure, but another possibility. Also inexpensive to replace if needed.=20

Hope this helps! Please advise.

Michelle Gagermeier, parts sales at Kit Components INC., phone 541-923-2244=
; michelleg@lancair.com, can fix you up with these parts if needed.

Bob P