A/c on?

i have seen remote car starters .would it be wise to keep my a/c on when i shut off my car,so when i use remote starter the a/c would be running already when i get in?

That is one of the reasons why people get remote starters installed on their cars, and it can be very helpful in terms of being able to get into a nicely cooled-down car. That is the good news.

The bad news is that these systems–particularly if the installer is not completely competent–is that damage to the car’s electrical system can result. If the car is still under warranty, I would suggest that you have the installation done by the Buick dealer, even if it costs more. Otherwise, you could be paying a large bill for repair work to the car’s electrical system if the remote starter installation does cause damage.

Edited to add:
Since it has been a while since Rivieras were made, I am going to guess that the car is not under warranty!

no not under warranty. but it has been garaged for 19 yrs. mint condition.1991 riviera so you think it would not hurt a/c compressor?

Nope.
No threat to the A/C compressor.

The only threat is from the guy hacking into the car’s wiring in order to do the installation. I suggest that you do some research in order to find out which installers in your area have been in business for at least 3 years.