Question: What size vacuum pump should I buy. Is 1.5 CFM enough, or should I spend the extra money for a 6 CFM vacuum pump.

You'll notice quite a wide variety of sizes and ratings when shopping for a vacuum pump. We feel you should look at the CFM rating in comparison to the primary use of the pump. You should also choose a pump which can achieve a deep vacuum based on the factory micron rating. Pumps that have a factory rating of 100 microns or less would make a good choice.

1.2 to 3 CFM - This range of pump is suitable if you plan on servicing the average car or truck. It's perfect for any single evaporator model between a Geo Metro and a Hummer H2. The advantage of the lower CFM pumps are ease of storage and transport. If you plan on doing on-site service, the footprint of the 1.2 CFM pump is hard to beat.

4 to 5 CFM - Good choice if you plan of servicing medium duty trucks, buses, or vehicles equipped with rear air.  This size pump provides a good balance between speed and versatility.  Vacuum pumps in this displacement class would be well suited for any high volume automotive repair shop.   

6 to 10 CFM - If you service or install air conditioning in trucks or buses that hold over seven pounds of refrigerant, 6 CFM or larger pumps are ideal.