Deciphering AC vent temperatures

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JHZR2

JHZR2

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So per my R-12 thread, the AC in my 240D wasn't cutting it yesterday in the low-mid 90s. With two adults and a baby, driving 50+ mph in full sun, we were very uncomfortable.

So I got a thermometer out to test... Wife's car said 86-87F, mine said 86F. This is all driving around town.

91 BMW 318i, R-12 retrofitted to R-134a: 60F
08 VW Rabbit, R-134a: 48F
81 MB 240D, R-12: 62F

I drove home today in the 318i, in work clothes and with full sun, and was very comfortable. Yet the temps in the 240 aren't far off and uncomfortable. The rabbit is very perfect.

I can't say I've ever had a car that I'd call "frosty" from the vents, though many claim to get 38-40 from the vents.

The 240 is low. Pressures on the 318 are fine for 134a, though perhaps a tad bit high given a retrofit.

So what's right? I've never seen 38F on any car. Should all cars, in their original design, blow roughly 40F at 85 F or higher??

Thanks!
 
How did you measure your AC vent temps?

And, I have a different question: Mine presently blows cold and works, and I want it to STAY that way!
 
Where were you placing the thermometer/probe?

FWIW, some cars just have weak AC systems. Not sure why that is -- seems like something easy to engineer at the factory.
 
are they condensing though, i.e. is water dripping underneath? I've found saturated air boxes that although were blowing somewhat cool, were so full of water from a clogged drain that the air was too "wet" to remove humidity.
 
42-52f is good. I just did a Subaru R134, full 30 min vac and 24oz R134 (spec is 21-25oz)
5 min = 6c (43f) at the vent compressor on, compressor cycling = 10-11c (50-52).
Very comfortable in 90-95f heat.
 
to answer your question a loose rule of thumb is 30'f under ambient is usually considered good so at 85'f, 55'f should be comfortable.....provided it's removing the humidity. Look for the drip sir.
 
Those temperatures are pretty unimpressive IMO. I consider anything above 48 degrees unacceptable.
I converted my Accord to R134a 2 years ago and the temps are usually between 42 and 46 degrees.
My Ranger has the best AC I've ever experienced. Vent temps usually get down to about 38 degrees, sometimes as low as 33 degrees on cooler days.

I think the truck has spoiled me and I now expect all cars AC to be as good as it. I wish the Accord's AC was a little better, but considering it has a bigger space to cool and it's not quite designed for R134a, I can't complain.
 
what happens to the vent temps if you squirt the condensor off with a water hose? If the temps drop quite a bit then it is typically an air flow/cooling issue.....maybe junk/gunk between the radiator and condensor?

One other thing to check is the blend door closing all the way and, depending on the humidity, car set for Recirc instead of fresh air?
 
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30 degree drop from ambient is good with r134, it takes a considerable amount of time to cool the interior of the car down to get an accurate reading. The ducting, vents and everything else absorb the cool air. Take it on a good drive at road speed with it on recirculate. Or set in the shade on recirculate for 30 minutes or so. If it doesn't have an electric cooling fan have a look at the fan clutch.
 
My 225K mile Escort Zx2 will blow 55* sitting still in 103* and moving it will get down to 40*-42*. it will give my knuckles frost bite..lol This I'm perfectly happy with. The truck hovers around 42* regardless if I'm moving or not.
 
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Fords are known for good AC. As I stated in your other thread my old van blows 39 F up into the 90's outside. I have never tested it above 92 degrees F outside.
Older vehicles if they have been charged several times (slow leak) can get moisture in the system. So even if the pressures are fine they won't blow cold enough. Fix the leak and thoroughly vacuum.
 
OK, interjecting a Q: If your car blows nice and cold when it is supposed to, how do you KEEP it that way?

Has been UBER humid in NJ/PA.

I feel bad for Floridians.
 
Originally Posted By: TechnoLoGs
OK, interjecting a Q: If your car blows nice and cold when it is supposed to, how do you KEEP it that way?

Has been UBER humid in NJ/PA.

I feel bad for Floridians.



You leave it alone until there is a problem.
 
Its temperature AND flow. It could be blowing 0*F air through a straw and you would be hot. Or 60* air through an industrial centrifugal blower, where you would be uncomfortable in seconds.

At the end of the day its just a heat pump, more fluid(refrigerant)=more heat removed. My 99 Prizm for example would actually freeze you out of the car before the compressor started leaking, on a 90* day, because that little car has something like 28oz of 134a in it and heat exchangers to match. R12 is better at carrying heat, most conversions dont do well because the condenser isnt big/efficient enough for 134a.
 
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In 90 degree weather my civic puts out a pretty consistent 40 degrees when cruising . My other cars are closer to 45.
 
Originally Posted By: spasm3
Originally Posted By: TechnoLoGs
OK, interjecting a Q: If your car blows nice and cold when it is supposed to, how do you KEEP it that way?

Has been UBER humid in NJ/PA.

I feel bad for Floridians.



You leave it alone until there is a problem.


And even if there is a problem, leave it alone until you have a gauge set and know some about auto A/C.
 
Well I wasnt cruising in any of these situations, just driving around town, the cars were fairly heat-soaked, etc.

The VW was more than comfortable with its temperature. Not quite 40F drop, but over 30. Never touched the system, and Im not sure I care to try to add 134a, would rather leave it closed. Its comfortable.

We never run on recirc for the most part... I dont think it works on my 318i, and I dont have an option on the 240D.

I think it all is what it is, other than the 240, which will get some R12.
 
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