ventilation for thru wall AC - please help...

I have a thru-wall AC unit in my condo, but after about 5 minutes of use, the compressor shuts off. The fan keeps blowing, but no cold air.

I thought it was a ventilation issue with something overheating and an auto shut-off triggering, so I pulled the unit out of the window and ran it completely unobstructed. The unit operated beautifully and so I know it's definitely a ventilation issue rather than a busted AC.

I think the problem is the exterior vent, which looks to be too small for the unit I have. It's only the size of half the back-face of the AC and there's metal slats and metal mesh across it to keep out water and bugs. I'm assuming one solution would be to make the vent bigger, but since I live in a condo, I can't easily rip out the vent without talking to the condo association about changing the exterior of my unit. I also don't want to pay for major work if I can avoid it.

Here are some pictures of the unit, the hole/setting in the wall and the exterior vent. I think another possibility is that that maybe the hot air is getting stuck in the gap between the back of the AC unit and the vent/exterior wall. (There's about a 4-inch gap which you can't see too clearly in the pics)

Questions:

• 
  Will it help if I build a funnel that leads from the back of the AC unit to the vent?

• 
  What other options would I have for venting the unit?

• 
  Am I on the right track with what's causing the compressor to shut down after a few minutes?

The AC unit is an AMANA AAC182STA

Thanks in advance for the help!

Jim

Welcome Jim:
Yes, your ventilation is seriously hampered. Not only is it not large enough to exhaust but the grille in the top of the case has to let air into the unit in order to blow out over the condenser coils. Apperantly the wall is too thick for this air conditioner.
Glenn