Don Maxwell Aviation Services, Inc.
Authorized Mooney Service Center
Most all long body Mooney’s, M20 R, S and M models, without G1000, have an electric standby vacuum system mounted in the avionics bay.
Recent failures of these systems have been caused by the deterioration of the Tygon hose that connects the vacuum pump to the vacuum manifold on the firewall.
The Tygon hose Figure 2 is routed behind the pilot side interior panels and is only visible near the firewall connection and at the rear mounted vacuum pump. The hose is a yellowish colored vinyl type tubing.
Over the years the Tygon tubing begins to melt, and it secretes an oil-like contaminate. This oil makes its way into the vacuum pump during operation and will seize the pump making it inoperable. Figures 3, 4, 5
We have found dozens of systems to be in this condition. Mooney has released Service Bulletin M20-317 to address this problem. It incorporates the replacement of the Tygon hose with a standard MIL-H-5593-10 vacuum hose.
We encourage all owners of these models to check for hose deterioration. The service bulletin can be found on Mooney International website: https://www.mooney.com/en/Support.html
Click on technical publications and select your model. M20-317 is the same for all models.
Standby vacuum system contaminated hose
MIL-H-5593-10 vacuum hose