Cadillac Repair: 1988 eldorado, climate control, perfect thing

Question
I have a chance to purchase a 1988 eldorado for a reasonable amount ($1000). It had 135000 miles on it, but the body and interior are almost perfect. Thing is, the Check Engine light is on constantly. I know the a/c needs a charge and while it idles smoothly, it's a bit rough when accelerating. What I'm most worried about is that it will fail the Emissions Testing that the State of Maryland performs. If it fails, then the registration is suspended and the tags will eventually be revoked. What should I have checked to fix that Check Engine light? Tyia for your help.
- Cindy

Answer
You need to check for computer codes via:

1. Ignition ON, Engine OFF.

2. Simultaneously push and hold the OFF and WARMER buttons on the climate control panel for 3 seconds and release them.

3. CODES will start to appear along with the word CURRENT or HISTORY for EACH code that displays. Write them down EXACTLY as they display on the screen and then the codes will stop at ECM?

4. turn ignition OFF