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 cycle the Master, the motor CB, and the motor switch, provided no help. So I flew back to AZ unpressurized. After landing, the motor operated normally. Any 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 manual that was changed over time, and some by "original" thinking. All I have seen have one function in common: The door seal pump is wired in series with 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 below 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 the pump off automatically. The pump is powerful enough to "explode" the seal if it's inflated with the door open and the pressure switch set high enough, so some caution when testing/working on this system--you can quickly create 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 the electrical pressure switch itself. The switches supplied by Lancair were "automotive quality," and while "good enough" for non-critical uses, are subject 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 continuously for an extended period could indicate a leak in the door seal--perhaps only when under pressure-- or a blocked inlet port to the pump--keeping it from drawing air to compress. The third component that might have caused what  you report is the (mechanical) door pressurization switch. For most installations I've seen, the pressure pump output is connected directly to 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 when power is applied, until the line pressure to the switch reaches the pressure 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 in an intermediate position, or if the internal shuttle "hangs up," it can port pressurized air from the pump directly out the vent. A less likely failure, but another possibility. Also inexpensive to replace if needed. 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