1997 Ford Explorer - AC Problem

[Robobru]

Our 1997 only has 50,00 mi on it and in the last 2 weeks the AC has stopped working. Compressor clutch does not click in but can hear the engine surging.
Does this mean recharge time? Or some other $$ problem. Anyone know if legal to recharge on own in Canada?
Noticed the filter cannister is rusty, could this be source of lost charge? Or how and why does system lose charge?

[Robobru]

Update - Went for a long hot ride today and then fooled around with the switches. Clutch kicked in when I plugged the low limit plug in and out a couple of times. AC worked for about 15 mins on the way home but then quit until I got home then I jiggled the plug again.