warm after 15 minutes. nice and cold until then??
ok, here are a few things to check..
1. refridgerant level (borderline low could cause that)
2. blend door (not staying in proper position).. check vacuum sources and check vavles.
3. again, blend door related, not in proper position at all, and when engine gets warmed up good, your actually getting hot air from the heater core mixed in with the cold air from A/C.
4. EATC (and its appropriate sensors). on my 91, they are the cabin air temp (located above glove box), and sunload (on dash, near speakers, but not sure if left or right is the sunload sensor, and other one is for autolamp)
Assuming that the EATC is working properly and the heat properly adjusts during winter (it shouldn't blow full hot all the time, it should vary to maintain cabin temp), then I will go with #1 as prime cause.