Navigator front suspension not kicking in

2005 Lincoln Navigator, 105000 miles, air suspension pump for front does not kick on every time when car started. Took car to non-dealer shop and they spent 2 days looking at all items. Stated no leak in bags, pump was working, no leak found in lines, all power connections good. They replaced 1 O ring at pump cannister and the problem went away. Drove for 5 days and it started happening again. Wife goes to start car in morning and pump will not kick in to inflate after sitting in cold all night. Pump does seem to work later in day, but not after sitting all night. All bags hold air and height when inflated. Since we have gotten car back from shop, it has not worked on 2 mornings, both of which the temp was below 10 degrees F. I have also noticed on a couple occasions that pump will not kick in until car is put in gear. No codes were showing when shop worked on car. Shop did not seem to have much knowledge of system, so I dont want to take back, but am leary to take to dealer due to possible high cost. Also, I tried to submit this question 5 times with a donation and web page wouldnt let me.