Thank you for the reply. I was waiting for you to chime in and you did.
First off, I added refrigerant because it had the exact problem -- AC works for a while then blows ambient air when it's hot. Not even having the limited knowledge about AC I have now, I talked to a friend and he said due to the age of my car it was likely low on refrigerant. He told me adding R134 was a piece of cake so I did it.
Second, on the fan came on when I jumped the switch. Now that both you and Rod thought it's strange, I think I will need to double check. I really only heard a clicking noise when I jumped the switch and assumed it was the fan coming on. When I did the test it's already a little dark and definite without sunshine, I might have taken the sunload sensor out of the equation as you suggested.
Now I think about it, the noise might be the clutch trying to engage but failed to do so? Is that possible?
I think I will follow your advice and try to locate where the sunload sensor is in my particular model and do some test.
When it's truly hot, the AC would not come back on even after cooling off. The day I did the jumpering test, I came back from work at 5 PM and did the test after dinner -- a good 2 hours later -- and the clutch did not engage. That day was really hot and at 7PM the ambient temp was 95F. For a day this hot 2 hours may not be enough to cool off I guess.
No, I do not see much sweating and frosting under the hood. How/where do I measure the temp of the cold air?