[A/S] keep old A/C or Replace

[clifs@xxxxxxxxx]

I have a 30 year old armstrong unit in my airstream.  It blows very 
cold, but the volume of air is low (on high setting) compared to 
todays A/C.  Is this volume normal? 

I am considering replacing with new unit, since I live in Texas where 
it gets hot, and simply because of its age.  I don't want to be out 
camping and have it decide to croak.  I just bought the trailer and 
have not been able to test its capability since we are in fall now.

My question to you all is; How reliable are these units at this age? 
And are any of you still using as old are older units?

Thanks.