DO NOT DO THAT!
If you use compressed air in the propane lines you will make sure the dealer can send his kids to college on your dime.
Even with low pressure you can burst the regulator and/or clog all the jets in your appliances.
I burst two regulators trying to troubleshoot mine. Turned out I had a bad pigtail and by trying to "blow it out" I destroyed my propane system. I had to replace the bad pigtail, the red high pressure regulator on the driver side AND the switchover regulator with both check valves.
A word to the wise.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW