They'll do that when they're a little low on refrigerant. 

Your Temp, Mode, and Inlet actuators are electrically controlled. So it isn't about a vacuum issue.

You know they're working because it blows cold on that side at idle.

Your Park Avenue holds 35 ounces of R134a. A can of R134a is 12 ounces. (1/3 the entire capacity)

You don't want to add too much so be patient. Put 1/2 a can in it and drive it. If it needs more add the other 1/2.

Get the R134a with UV dye (not leak sealer). The refrigerant doesn't "disappear". It leaks out. The UV dye may help you determine where it's leaking.

Before you do anything, if you haven't already touched it, get yourself a set of manifold gauges, they're $60 at Harbor Freight, but you can rent one at an auto parts store for free. Hook the low side and high side up to the gauges and run the system for about two minutes. Figure out the ambient temperature and find a chart on Google of R134a pressure vs temperature readings. Compare them to your readings. Add R134a until the pressures are close to what the chart says, if the system is low. Only use straight R-134a or R-134a with dye, no stop leaks. 

Don't use the cans with a low side gauge and hose. There is no way to purge the hose of air and moisture, which will slowly damage the system if it's allowed in. Check the pressures against your chart in a few days and see how the pressures change relative to the chart. That will tell you if you have a slow leak.