William,
A tweak on the pressure switches won't do it. I think Wolfgang's list of remedies is correct, and Chris Zavatson has the full analysis and the kit that will modify the pump (I haven't tested, but his analysis makes sense to me).
Just one little note -- this can happen in reverse too. An airplane that's landed on a cold day... and launched on a warm morning following -- can have gear *retraction* failure, as I know to my extreme discomfort on an occasion when I took off into a low overcast, pointed straight at DFW 9 miles away, with an immediate heading change, freq change, etc. It was necessary to revert to basics: FLY THE AIRPLANE before figuring out why it wasn't climbing and cracking the dump valve.
I haven't modified my hydro pump yet, but I plan to; until then, every preflight includes "Cycle the dump valve". This relieves any pressure buildup that may have occurred since the previous flight.
Charley Brown
Legacy #299 330hr
I believe that I recently experienced something in my Legacy that I remember reading about but can't remember all the details. I looked into the LML archives and was unsuccessful. Could someone out there please briefly summarize the situation, reason and any possible remedies for gear extension failure following high altitude cruise in cold air followed by a decent and landing in hot air. I seem to remember a discussion about boosted pressure in the hydraulics plumbing due to the rapid rise in temperature which in turn had an effect on the operation of the pressure switch In my recent experience...after opening the dump valve, the hydraulic pump did run, confirming continuity to the pump. After working the nose gear into the locked position, the landing was uneventful but I would like to avoid this uncomfortable situation in the future. Would a tweak on the pressure switch adjustment be called for here or just expect to momentarily crack open the dump valve to relieve excess pressure. Thanks for your thoughts.