Does my husband have to slow down to below 40 mph before flipping on the AC?

Dear Car Talk

Dear Car Talk | Mar 01, 1997

Dear Tom and Ray:

It seems there are two schools of thought (mine and my husband's) on when the air conditioner can be turned on with the engine running. I say it can be turned on at any speed. He says you need to slow down to at least 40 mph before flipping the switch. Am I right, or what?--Jennie

RAY: You're right, Jennie. You're right, already!

TOM: This is a sore point for us, because we used to agree with your husband. We figured that since the air-conditioning compressor is run by a belt driven by the engine, you'd be better off turning it on at lower speeds, so you didn't "jolt" the compressor into action, right? After all, who likes to be jolted into action? Not me!

RAY: You? You don't even like to be gently lulled into action!

TOM: After we gave out this eminently plausible explanation on our NPR radio show a few months back, about 100 air-conditioning technicians and engineers wrote to us and told us what morons we were.

RAY: And while we get that sort of feedback after every show, this time our critics had a viable counter argument. They said that since the air-conditioning compressor cycles on and off frequently on it's own, it's designed to be "jolted" at any speed, at any time. According to lots of engineers who wrote to us, the compressor clutch is designed to be heavy duty enough to take this punishment, and is not at all bothered by being "jolted" to life at 60 mph.

TOM: So, Jennie, this means you have every right to ask your husband to "assume the position: " Waistband up around his chest, shoulders shrugging demurely, chin down, eyes up, and muttering "yes, dear."

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