AC not as cold on hot days?

[do0dfromcali]

Heres the deal:

If my car sits till mid afternoon when it has been baking in the sun all day and I get in and start it up, the a/c is not as cold as it usually is. Even after running for about 10 minutes. If I get onto the highway and start cruising around 75 or so, the a/c gets to the cold level that it should be.

If I get in my car early morning before it bakes in the sun or gets super hot out, I can run the a/c and it is super cold. But once it sits in the sun, it takes awhile for the a/c to cool itself down.



I am just curious if this is common in older cars or there is something I can do to prevent it. The a/c is already converted to r-134a and was checked and there were no leaks.

This one seems like a head scratcher since the a/c isn't out of free-on but acts like it is when it is hot outside on the initial start up.

[crewfish13]

Nothing too difficult here - when the AC is running inside a really hot car, the air it cools starts out hotter. Air conditioners in cars don't have a target temp, they just remove X-number of BTUs from the air as it flows through the coils. With air, this is a pretty linear relationship of BTUs of enery contained vs. temperature. So, although it cools it the same number of degrees, the end result is higher. I'm almost positive the cabin air is sucked from right behind the hood, so if the hood's hot, the initial air will be hot.

Once you're really moving on the highway, convective cooling takes over from the conductive, and cools the entire car much more efficiently (think of the difference between sitting in a hot room and sitting in a hot room with a fan blowing on you). Because everything, especially the hood, has much better cooling air flow, and the air just above the hood is cooler due to less heat soak (due to shortened exposure time) the "pre-AC" air is cooler.

[mrvinyl33]

I've noted this effect was greater after switching to R134a.

[accordme93]

This is the problem I had on my A/C. I had it recharged and it gets very cold now even on 100 plus days. Granted, it's still R12. I was lucky and got the hookup!

[SteveB]

Once you're really moving on the highway, convective cooling takes over from the conductive, and cools the entire car much more efficiently (think of the difference between sitting in a hot room and sitting in a hot room with a fan blowing on you).

The temp hasn't changed though, fan or no fan.

It cools better when moving because the condensor has better airflow.

[NAiL05]

What steve said I would go with a condensor. It could be clogged up. Try gettin a garden hose and spray it down and see if the temp goes down if it does you just found your problem.

[xaxis360]

I agree about 134a. R-12 in the A/C for our cars kicked ass. My previous accord still had R-12, it was colder and worked much quicker than my 134 coverted ride.