A/C doesn't work under 40mph?

soph584 · #1 (**permalink**) 05-17-2009, 06:16 PM

I have recently noticed that my air conditioning does not work until i accelerate to 40mph. The air will be hot and then when i hit 40 the cold will kick in and then when my speed decreases to under 40 it will be hot again. Does anyone have any ideas as to why my car is doing this/ what it would cost to fix it?

everyman · #2 (**permalink**) 05-17-2009, 10:38 PM

Quote:

Originally Posted by soph584

I have recently noticed that my air conditioning does not work until i accelerate to 40mph. The air will be hot and then when i hit 40 the cold will kick in and then when my speed decreases to under 40 it will be hot again. Does anyone have any ideas as to why my car is doing this/ what it would cost to fix it?

It's not atypical behavior for automotive AC. Both speed and RPM will have an effect on the system's cooling ability. Speed because it moves more ram air across the condenser coil to exchange more heat. RPM because it pumps the pressure higher. Are you saying you've just noticed it, or you are certain it's never done it before, and it has just started?

If the latter, it's certainly possible that you are low on coolant. My '00 just had it's AC worked on 6 months ago, and it behaves pretty much the way you are describing. I generally run with the air exchanger set to recirculate, when I'm putting around town for this reason. The air gets to pass through the system over and over which quickly lowers the temperature in the cabin. Then when it's cool I might switch it to fresh air so I don't pass out from oxygen deprivation.