Hello, it is not a good idea to replace just the outside unit. 1. to small to match the new cond. 2. contaminants.
3. often dirty & plugged. 4. old dirty oil trapped in evap coil. 5. old line set often too small & dirty.etc
a reputable contractor would never recomend such a decision unless it is impossable to change. pay someone who knows what they are doing. you will not regret it. Carrier & rheem dealer