Herman K

With an ambient outside of 95+ plus today the temperature at the center nozzle comes down 38-40 degrees F (driving the car) with the fresh-air blower set at stage 2.

However when I go to stage 3 or 4 (increasing the amount of airflow over the coil) the temperature measured at the center nozzle rises 5-10 degrees?

Question; Why...is this and indication that a need a little more freon in the system or...

Kevin in Atlanta

Uh, no it means that the air passes too quickly over the evaporator coil to pick up the coolness. Had that issue with 1981 Prelude - complained to Honda and they said to not have the fan on max - and they were right.

dprantl

Think about it from a physics standpoint. The A/C evaporator removes heat from the air passing through it. The faster you blow the air through there, the shorter the time the air is in contact with the evaporator fins to shed its heat energy. Also, even the best A/C system can only drop the air temperature by a certain amount of degrees. If the input air to the evaporator is 95 deg F, the output will be ~60 deg F. Recirculation is key in this case so the A/C system can keep cooling the same air more and more until the target temperature is reached.

Dan
'91 928GT S/C 475hp/460lb.ft

RKD in OKC

If I leave my fan on 2 with A/C on and the ambient temp is anywhere within dew point, it blows fog out the center vent.

Herman K

Thank you guys for the feed back on this. I'll record some different data -points with an infrared laser thermometer during my Houston - Dallas (OCIC) drive this Friday (using recirculating and other settings- like footwell only with varying different fresh air stage settings etc.)

dr bob

Herman--

The IR temp gun has a tough time reading air temps at the vents. It reads the plastic flaps and doors OK, but is woefully inaccurate for gas temps. A better choice is a kitchen/refrigerator thermometer. I use a cool little digital unit that's under $15 most kitchen supply places. It has peak holds for highest and lowest temps, and a probe that fits in the center vent ductwork nicely. Other option is the standard pocket AC dial thermometer, about $8 at better autoparts places. I use three of them when testing AC systems. Ambient, pass side floor air temp, and center vent temp will tell you a whole lot about your system performance.

Herman K

Thx Dr Bob I'll look forward to discuss some of this with you in Dallas this week, have a save trip!

Randy V

Correct. With a digital meat thermometer my center vents read 32.5 F, but read 26 F with the IR gun.

Herman - you will also notice warmer temps at the center vent when you turn on the rear AC system.

dr bob

I'm stocking up on ice cubes for the trip. Just in case...

Might bring a few toys for show-and-tell. Thermometer rides in the glovebox at all times anyway. Maybe a theory clinic followed by a hands-on tour will be available. We should have enough gurus of the various systems to host some pretty detailed tech discussions. Or we could visit, enjoy the company, and leave the 'problem' at home for a couple days. I'm game for anything, really.

Herman K

Dr Bob, that spirit and attitude alone make it worth the trip. Look forward to meet all of you have a save trip!

LGL

In a closed system, Q(heat transferred)= mass air flow times (Air Temp minus Coolant Temp) times c ( a constant) so an increase in fan speed will always increase the heat transferred from the air in your car. And entropy always increases.

Alan

But increased heat transfer does not equate to lower vent temperatures since its both a volume and temperature question.

Alan