From: ghg@cidmac.ecn.purdue.edu (George Goble)
Newsgroups: rec.autos.tech
Subject: Re: A/C output temp?
Message-ID: <3rjpqv$366@mozo.cc.purdue.edu>
Date: 13 Jun 1995 10:38:23 GMT
Organization: Purdue University Engineering Computer Network
Lines: 28

In article <24.52300.2645@pcohio.com> danny.fitzsimon@pcohio.com (Danny
Fitzsimon) writes:

 > >Does anyone out there know what the temperature of A/C air at the output 
 > >vent should be? Assume A/C set on max. and outside temp. of about 80 
 >
 >
 > JW> On an average 6 to 10 C would be about normal...
 >
 > Or about a 40-45 degree "pulldown" as measured by the pass. fr. vent.
 > Say, about 40 degrees min.  at 80.  At idle, it might take the system
 > 15 mins to cool the ducts, evap, etc.  Warning: your coldest temp might
 > not be a the highest fan speed.
 > 
 >Danny

A/C on "Max (recirc)", fan speed on high, 90F high humidity outside, sunny.
cold air 1/2 block after engine start, have to slow down A/C after
a mile, since cold air is starting to "burn" (28F air), breath
steaming, etc...humidity in front seats goes from 80% -> 30% in
4 mins.. 1990 Pontiac Transport, GM V5-compressor.. no changes
to the A/C system (except for the refrigerant).

This refrigerant, a modified form of R-406a (65% R22 instead of 55%),
back in 1990, was one of the various blends I made up, and is still
in the car.  It is not legal for cars in the US anymore. It was
"grandfathered in".. since it was invented/installed before the
Clean Air Act or EPA SNAP existed.
--ghg

From: ghg@cidmac.ecn.purdue.edu (George Goble)
Newsgroups: rec.autos.tech
Subject: Re: A/C output temp?
Message-ID: <3rlrpk$st9@mozo.cc.purdue.edu>
Date: 14 Jun 1995 05:24:04 GMT
Organization: Purdue University Engineering Computer Network
Lines: 95

In article <3rlhgp$nej@netaxs.com> rbanks@netaxs.com (Robert Banks) writes:

>What do you do when the evaporator freezes up like a block of ice. 
>If the air temp coming out of the evaporator is 28F, the the evap must be 
>slightly colder. When you "slow down A/C " I assume you mean the fan speed,
>this is a great ice block maker for the evaporator.
>
>
>Robert Banks
>ASE L1 Master Tech

You are correct about having to worry about ice.. TO get 28F air, the
evap runs at around 18F.. and sure enough the suction line frosts up
all the way back to the compressor, including the suction accumulator..
If you have an R-4 or other cycling type compressor, the evaporator
clears of ice quickly during the compressor off cycle.. no problem.
If you have a continuous run compressor, such as a GM V-5, then the
evap will freeze up for sure.. In city driving, stopped at a light
lets it warm up to 34-36F or so, so the ice melts.. but in out
on the interstate, it freezes up in about 20-30 mins..
Flipping the system over to "VNT" clears the ice in 15-20 sec..
and sometimes makes a bunch of "fog" coming out the ducts..

Dependent on both humidity and fan speed and/or recirc.. vs
outside air for the lenght of time for ice up.  Head pressures
drops way down during an ice up (suction stays at 28 due to
variable displacement compressor backing off), and since very
little heat is rejected to the condenser, it cools off and
the head drops way down (on the highway). (gauges & thermocouples
installed inside the car, with copper lines).

It would seem easy to build a device to stick in the compressor
clutch 12V line, to off the compressor for 15 sec every 3-4 mins
to keep ice under control..  I think it would be worth this
hassle for a "maximum performance" refrigerant in very hot
and humid climates..Nothing beats almost "instant" cool air
when your car has been baking in the sun.. no frustrating
mile or two to get cold.  A mandatory hi-pressure cutout switch
is needed here (car has one)..as it is possible to hit 400-450
PSIG on the head under some startup conditions, stuck at light
with poor condenser air flow, etc..  Compressor discharge temps
were measured in the 245-255F range during "stress" tests
(racing the engine while not moving), this is about the limit
the refrigerant can handle.

After the initial cool down, I usually add some "heat".. move
the lever about 1/3 the way between cold & hot.. and slow
down the fan.. This may sound stupid, but it is a super
dehumidifier.. You are still max cooling the air to remove
the moisture and then adding some heat back, so you dont
freeze.  After a while "max cool" in this system feels like
it is "burning" you (too cold) unless you add heat.  I have
been the butt of never ending jokes about causing pneumonia,
etc, in the middle of July.. It is a terrible shock when you
get back out of the car.  It also promotes horrendous "fungus"
growth all over the insides of the air duct system..
Need to battle that with spraying Lysol into outside air
inlet duct (running A/c on "normal"), or run VNT-only to
dry out the ducts before leaving car overnight.

Oddly enough, the "limit" for increasing capacity with this
type of refrigerant, appears to be one with the car not running.
About 30-45 mins after you park, on a hot day, even if you were
not using the A/C.. there is  huge pressure buildup in the system.
While driving the condenser may be the coolest part of the system
(air is off), and the refrigerant will migrate there.. Upon
stopping, you get a "heat soak" of the condenser from the
radiator (depends on wind also?).. Your A/C acts as a "heat pipe",
and pipes the condenser heat into the evaporator, where it
can't get out easily.. so it just gets hotter.. Maybe the reverse
happens in the SW with a dark interior??  The "heat pipe"
effect will tend to move heat between hot to cold parts
of the system, while off.  A GM style "accordion" type
evaporator can only take about 175-200 PSI before it
breaks (from experience, pressure tests, etc)..  The heat pipe
heat buildup causes 150-175 PSIG about 45 mins after parking,
would could bust your evaporator.. This limits how much R-22
you can add to bring up the capacity..


Only 3 cylinders (50 lbs each) were ever made of this..
One went to Solvay in Germany, I kept one, and one went to
Walt Pasko in Florida.  Walt told me once that
"there ain't no such thing as an air conditioner too cold
in Florida".. This was my answer to that bet.  All this took
place back in 1991, back before the entanglements of EPA rules,
Clean Air Act, MACS, etc, etc, took hold.

THIS REFRIGERANT IS NOT LEGAL ANYMORE IN THE US (for cars). Installing
it now can get you a $25,000 fine.. It is ok if left alone in
the 1991 test cars. It was called "GHG-HP (Hi Performance) Refrigerant-12
Substitute" or something like that..

--ghg (inventor of R-406A)
http://ghg.ecn.purdue.edu