My 2009 Toyota Corolla's a/c intermittently doesn't come on when I start the car.

you have a delay system. most cars that i have found that sit out in 90 degree weather will take a little time for the system (compressor) to adjust for the temp you have set.

Here is a good read on the subject...http://www.underhoodservice.com/a- c-update-the-logic-behind-automatic- temperature-controls/

Delay system? If it does, please explain that tracerfire I am open-minded and always ready to learn. But my Corolla will blow popsicles in less than 2 -3 minutes at idle, even at 100°+. See page 184 in link below. BTW, if you register your VIN at that site, you will have access to all service records, (except those done yourself, and even they can be entered), and much more. I Suggest signing up there at that Toyota's owners site. They even have a Q&A forum.

http://www.toyota.com/t3Portal/document/om/OM12C16U/pdf/sec_03_01.pdf

A/C problems can stem from many issues. O-rings, seals and hoses Compressors and compressor clutches Evaporators and condensers Driers, receivers and accumulators Switches, controls, modules and relays Blower motors and resistors etc. Freon is responsible for cooling your car. Freon is a halocarbon that cycles through your A/C. Freon is a refrigerant that cycles through liquid and gas phases, and works to regulate the temperature of your car. It is important that there is not an A/C Freon leak in your car’s air conditioner system, in order to maintain cool air temperatures in the vehicle’s cabin when the air conditioner is on.