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Date: Thu, 19 Jun 2014 07:39:52 -0700
From: Brent Regan <brent@regandesigns.com>
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To: Lancair Mailing List <lml@lancaironline.net>
Subject: IV P door seal
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There are two possible problems. Bob P. gave a good description of the 
pressure switch. In your case the pressure switch contacts could have 
'welded' shut. The other, and IMHO more likely, possible problem is that 
you have a leak in the plumbing or the manual pneumatic switch. When the 
master is on the pump gets power via the pump breaker and pressure 
switch. If the pump is running then you have a good circuit. If the pump 
doesn't stop running then you either have leak or a bad pressure switch. 
The compressor keeps the switch pressurized all the time. The manual 
pneumatic switch simply connects the door seal to vent OR to the 
pressurized circuit.

Find the pump / pressure switch in your plane. Pinch off the hose that 
runs to the manual pneumatic switch. Turn on the master. If the pump 
runs and stops, you leak is downstream. If the pump loads down but 
doesn't stop the problem is the switch. If the pump does not load down 
then look for the leak around the pump.

Brent Regan


On 6/19/2014 3:00 AM, Lancair Mailing List 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?