A/C Vent Temperature Test:

[Doktor Bert]

A very scientific test...

Air-Con Mega Test: Discover the car with best air conditioning system

[Doktor Bert]

I can get my R-12/R-4 equipped W116 down to about 35°F in the vent with 28°F grille surface temps at 100°F ambient with 22% humidity @70 mph, but our 2000 Ford F150 (with custom A/C tuning) will put out 28°F vent temps with 19°F grille surface temps at 100°F ambient and 22% humidity @ 70 mph, which is as cold as I have been able to get any A/C system to work....FWIW

[vstech]

what's the air flow pressure on the F150? dem's some COLD numbers...

I build refrigerators and home and commercial HVAC systems for a living... I can make a 134 system put out as cold air as I want, but 19F at the registers just sounds CRAZY... how's it keep the condensate from freezing the coils?

[Doktor Bert]

Originally Posted by vstech

what's the air flow pressure on the F150? dem's some COLD numbers...

I build refrigerators and home and commercial HVAC systems for a living... I can make a 134 system put out as cold air as I want, but 19F at the registers just sounds CRAZY... how's it keep the condensate from freezing the coils?

We always see vent grille surface temps lower than the air register temps. I think our max humidity here is around 22-25% and that's probably too low to ice the fins????

[Phillytwotank]

100% stock system '78 300CD. R12 refrigerant charged by VStech last march.
This morning. 92% humid. 70f ambient. 60mph.

55f air temp from the vents.

Is that good?

[tjts1]

My old Volvo 850 putting out 28f in the summer.
http://i.imgur.com/yKHMLBk.jpg

[compu_85]

Originally Posted by vstech

...but 19F at the registers just sounds CRAZY... how's it keep the condensate from freezing the coils?

That's what I'm wondering.

Our Passat can kick out 42*F air, I don't think I would want it much colder than that! That temp reading was at 91*f and probably 45% RH. As it gets hotter / more humid I'll take another measurement.

My Jetta can manage a 35* temp drop across the evaporator... I'm happy with that. It won't blow colder than 46* though. Both VWs use a variable displacement compressor, and the Passat is even fancier with a recirculation valve that unloads the compressor as the car temp reaches the setpoint on the ACC.

The Passat uses less R134a than the Jetta, yet is a bigger car and cools better. Ahh, the forward march of technology

Still need to get the rad fan sorted on the MB before I can post a result on its AC

-J

[jcyuhn]

Originally Posted by Doktor Bert

We always see vent grille surface temps lower than the air register temps. I think our max humidity here is around 22-25% and that's probably too low to ice the fins????

If the dewpoint is below 32F you can run the evaporator below freezing without generating any condensate, and hence nothing would freeze on the evap. I suppose this could happen in a desert climate, although I'm looking at noaa.gov right now and the dewpoint in Palm Springs is in the 50 degree range - not really all that dry.

You'll know if the evap freezes, it blocks the airflow. You can hear the fan whirring away, but nothing comes out the vents. I had the clutch cycling valve go bad on a Ford CCOT system and it would freeze the evap after an hour or so. It's no big deal, all you do is switch to econ mode for 5 minutes to let the ice melt. Shoot, you don't even lose cooling, the ice on the evap cools the airflow!

- JimY

[Doktor Bert]

Originally Posted by Phillytwotank

100% stock system '78 300CD. R12 refrigerant charged by VStech last march.
This morning. 92% humid. 70f ambient. 60mph.

55f air temp from the vents.

Is that good?

If you go buy the temp/humidity chart, I think you will find those temps acceptatble...

[vstech]

if the stock York compressor is only putting out 55F, the freeze switch may be adjusted too high. that car should be putting out lower temps than that, but humidity plays a huge roll in the vent temp output.

[Phillytwotank]

Ive had the feeling that it should be colder that that. Pressures look good.

Unsure the cleanliness of the evaporator and Ive not heard of this "freeze switch" you speak of. Maybe a couple of things to check out

[Equestrian]

My 91 300d will manage 28* on the highway with fresh r12 and the original compressor. Anything beyond that and the ccu starts cycling the compressor to prevent icing.
[IMG][/IMG]

[vstech]

What blower speed?

[MBeige]

At about 2500RPM, 85F outside temp:

With temp wheel set to 18C, the AC vent temps would average 5 deg C (range from 4 deg C to 6 deg C)

With temp wheel set to max cooling, the AC vent temps would average 2 deg C (range from 0 deg C to 4 deg C)

Blower setting in both cases set to auto. No glass tint on my car.