1973 OPEL GT-R ESP

7C-1341973 OPEL SERVICE MANUAL
Figure 7C-232
Torque Converter4. Rotate converter to check for free movement.
1. Place transmission on portable jack
2. Slide torque converter over stator shaft and input
shaft.3. Be sure that converter pump hub keyway is seated
into oil pump drive lugs and the distance “A” is
.20”to
.28”. See Figure 7C-232.
SPECIFICATIONS
GENERAL SPECIFICATIONS
Opel Three-Speed Automatic Transmission Fluid
RecommendationsUse DEXRON Automatic Transmission Fluid on/y
in all 1972 model Opel Automatic Transmissions
(GM part No. 1050568-69-70 or any other fluid hav-
ing DEXRON identifications).DEXIRON is an especially formulated automatic
transmission fluid designed to improve transmission
operation.
The oil pan should be drained and the strainer re-
placed every
24,ooO miles and fresh fluid added to
obtain the proper level on the dipstick. See subpara-
graph 2 for proper refill procedures. For cars sub-
jected to heavy city
traff%z during hot weather, or in
commercial use, when the engine is regularly idled
for long periods, the oil pan should be drained and
the strainer replaced every
12,ooO miles.
.
1.Checking and Adding FluidThe Opel three-speed automatic is designed to oper-
ate at the full mark on the dipstick at normal operat-
ing temperature (180 degrees F.) and should be
checked under these conditions. The normal operat-
ing temperature is obtained only after at least 15
miles of highway type driving or the equivalent of
city driving.
Fluid level should be checked at every engine oil
change.
The “FuIl” and “Add” marks on the trans-
mission dipstick indicate one (1)pint
difference. Todetermine proper fluid level, proceed as follows:
To determine proper level, proceed as follows:
1. With manual control lever in Park position start
engine. DO NOT RACE ENGINE. Move manual
control lever through each range.
2. Immediately check fluid level with selector lever
in Park, engine running, and vehicle on LEVEL
surface.At
t,his point, when a reading is made, fluid level on
the dipstick should be at the “FULL” mark.
3. If additional fluid is required, add fluid to the
“FULL” mark on the dipstick.
If the vehicle cannot be driven sufficiently to bring
the transmission to operating temperature and it

AUTOMATIC TRANSMISSION 7C-135
becomes necessary to check the fluid level, the trans-
mission may be checked at room temperature (70
degrees F.) as follows:
1. With manual control lever in Park position start
engine. DO NOT RACE ENGINE. Move manual
control lever through each range.
2. lmmediately check fluid level with selector lever
in Park, engine running, and vehicle on LEVEL sur-
face.At this point, when a reading is made, fluid level on
the dipstick should be I/4” below the “ADD” mark.
3. If additional fluid is required add fluid to bring
level to
l/4” below the “ADD” mark on the dip-
stick.If transmission fluid level is correctly established at
70 degrees F. it will appear at the “FULL” mark on
the dipstick when the transmission reaches normal
operating temperature (180 degrees F.) The fluid
level is set
l/4” below the “ADD” mark on the
dipstick to allow for expansion of the fluid which
occurs as transmission temperatures rise to normal
operating temperature of 180 degrees F.
Do not overfill, as foaming and loss of fluid through
the vent pipe might occur as fluid heats up. If fluid
is too low especially when cold, complete loss
of’drive may result which can cause transmission fail-
ure.
2.Draining oilpan and rep/a&g strainer assembly.
(a) Raise car on hoist or p/ace OnJxk stands, and
provide container to collect draining fluid.
(b) Remove oil pan and gasket. Discard gasket.
(c) Drain fluid from oil pan. Clean pan with solvent
and dry thoroughly with clean compressed air.
(d) Remove strainer assembly, strainer gasket and
discard.
(e) Install new oil strainer gasket. Install new strainer
assembly.
(f) Install new gasket on oil pan and install pan.
Tighten attaching bolts to 7-10 lb. ft.
(g) Lower car and add approximately three (3) pints
of transmission fluid through filler tube.
(h) With manual control lever in Park position, start
engine. DO NOT RACE ENGINE. Move manual
control lever through each range.
(i) Immediately check fluid level with selector leverin Park, engine running, and vehicle on LEVEL
sur-
face.(i) Add additional fluid to bring level to
l/4” below
the “ADD” mark on the dipstick. Do not overfill.
3.Adding Fluid to Fill Dry Transmission and Con-
verter Assembly
The fluid capacity of the Opel Three Speed Auto-
matic transmission and converter assembly is ap-
proximately IO-l/2 pints, but correct level is
determined by the mark on the dipstick rather than
by amount added. In cases of transmission overhaul,
when a complete fill is required, including a new
converter proceed as follows:
(a) Add approximately 10-l/2 pints of transmission
fluid through tiller tube.
The converter should be replaced on any major fail-
ure, such as a clutch or gearset, and an excessive
amount of foreign material is indicated in the pan. If
installation of a new converter is not required add
approximately five (5) pints of transmission fluid.
(b) With manual control lever in Park position start
engine and run at 1000 RPM. DO NOT RACE EN-
GINE. Move manual control lever through each
range.
(c) Immediately check fluid level with selector lever
in Park, engine running, and vehicle on LEVEL
sur-
face.(d) Add additional fluid to bring level to
l/4” below
the “ADD” mark on the dipstick. Do not overfill.
Opel Three Speed Automatic Transmission Towing
Instructions
If an Opel equipped with an automatic transmission
must be towed, the following precautions must be
observed:
The car may be towed safely on its rear wheels with
the shift lever in neutral position at speeds of 35 miles
per hour or less under most conditions.
However, the drive shaft must be disconnected or the
car towed on its front wheels if:
a. Tow speeds in excess of 35 mph are necessary.
b. Car must be towed for extended distances (over 50
miles).
c. Transmission is not operating properly.
If car is towed on its front wheels, the steering wheel

REFRIGERANT COMPONENTS ALL MODELS9s. 19
Figure 98.3 Effect of One B.T.U. on One
Pc’und of
water
teristics of heat if we think of heat as a sort of color-
ing dye. If we add one drop of red dye to a glass of
water, it will turn slightly pink. Another drop will
make the water more reddish in color (Fig.
9B-4).The more drops of dye we add, the redder the water
will get. Each drop of dye corresponds to 1 Btu and
the succeedingly deeper shades of red are like in-
creases in temperature.
Figure
98-4 Addition of B.T.U. Heats Water
It may seem a little puzzling to talk about beat in a
story on air conditioning but, when you stop to
think about it, we are handling heat exclusively. Al-
though we ordinarily think of an air conditioner as
a device for making air cold, it doesn’t do that di-
rectly. What it does is take heat away from the in-
coming air and transfer that heat outside the vehicle.
We know now that cold is nothing more than the
absence of heat, and that heat always flow from a
warm object to a colder one. We also have
:a clearer
idea of how heat is measured.
From everything we’ve learned about heat
EO far, it
seems to behave in a perfectly normal manner. Yetsometimes heat will disappear without leaving a sin-
gle clue.
Ice vs. Water for CoolingEtery once in a while in the old days, the ice-man
would forget to refill the ice-box. Occasionally, as the
last sliver of ice melted away, somebody would come
up with a bright idea. He would remember that the
water in the drain-pan always felt ice-cold when he
had emptied it other times. So, he would get the
thermometer out and check its temperature. Sure
enough, it usually was about as cold as the ice. Why
not put the drain-pan back in the ice compartment
to keep things cold until the iceman returned the
next day
It was a good idea. but it never worked. For some
strange reason the ice-box never stayed cold. The
drain water soon got quite warm and in a couple of
hours, the butter in the ice-box would begin to melt,
the milk would start to sour, and the vegetables
would wilt.
Why did this happen? The drain water was only a
few degrees warmer than the ice yet it didn’t draw
nearly as much heat out of the stored foods. How-
ever, the difference between the behavior of cold
drain water and ice is the real secret as to how any
refrigerator works and we can easily learn the an-
swer by using an ordinary thermometer.
When we put a drain pan full of cold water into the
ice compartment, we expect the heat to flow from the
warm foods to the colder water. Remember, that
heat always flows from a warm object to a colder
object and when we add heat to water, it gets
warmer. Each Btu of heat added to a pound of water
makes it one degree warmer.
Figure 98.5 Melting Ice Remains at 32 Degrees

98-20 1973 OPEL SERVICE MANUAL
If we were to put a thermometer in the cold drain
water, we would see the temperature gradually creep
upwards. That is to be expected because heat is flow-
ing into the cold water making it warmer. Before
long the water would be as warm as the stored foods.
Then the water could no longer attract heat because
heat will not flow from one warm object to another
equally warm object. Since we no longer can draw
heat out of the foods we no longer are cooling them.
Now, let’s see what happens when we put ice instead
of cold water into the ice-box. This time, we’ll set the
thermometer on top of the ice (Fig. 9B-5). When wefirst look at the thermometer, it reads 32 degrees. A
couple of hours later, we open the ice compartment
door. The ice block is smaller because some of the ice
has already melted away
- but the thermometer still
reads 32 degrees. Again, still later, even more of the
ice has melted, yet the termometer continues to read
32 degrees. So long as any ice remains, no matter
how much of it has melted away, the temperature of
the ice stays right at 32 degrees.
All this time the ice has been soaking up heat, yet it
never gets any warmer no matter how much heat it
draws from the stored food. On the other hand, the
cold drain water got progressively warmer as it
soaked up heat. Why is it the addition of heat will
make water warmer yet won’t raise the temperature
of ice above the 32 degrees mark? If we till one
drinking glass with ice and another with cold water,
and put both glasses in the same room where they
could absorb equal amounts of heat from the room
air, we will find it takes much, much longer for the
ice to melt and reach room temperature than it did
for the water in the other glass to reach the same
temperature. Obviously, most of the heat was being
used to melt the ice. But it was the heat that appar-
ently disappeared or went into hiding because if
couldn’t be located with a thermometer. To best de-
scribe this disappearing heat, scientists turned to
Latin for the right word. They chose the word “la-
tent” which means hidden.
Latent Heat
So latent heat is nothing more nor less than hidden
heat which can’t be found with a thermometer.
What happens to the latent heat? Where does it
disappear to? At first it was thought it was in the
water that melted from the ice. But that wasn’t ex-
actly the right answer because, upon checking water
temperature as it melts from ice, it will be found that
it is only a shade warmer than the ice itself. It is not
nearly warm enough to account for all the heat the
ice had absorbed. The only possible answer is that
the latent heat had been used up to change the ice
from a solid into a liquid.
Many substances can be either a solid, or a liquid, ora gas. It just depends on the temperature whether
water for example was a liquid, or a solid (ice), or gas
(steam) (Fig.
9B-6).Figure 99-6 Temperature Determines State of Water
If we put some water in a tea-kettle, set it over a tire
and watch the thermometer as the water gets hotter
and hotter, the mercury will keep rising until the
water starts to boil. Then the mercury seems to stick
at the 212 degrees mark. If we put more wood on the
fire, despite all the increased heat, the mercury will
not budge above the 212 degree mark (Fig.
9B-7).Figure 98.7 Boiling Water Never Exceeds 2 12
DegreesEven though many housewives won’t believe it, no
matter how large or hot you make the flame, you
can’t make water hotter than 2 12 degrees. As a liquid
changes into a gas, it absorbs abnormally great
amounts of heat without getting any hotter. Here is
another instance where heat disappears.
Now we have two different kinds of latent heat,
which are quite alike. To keep their identities sepa-
rate, the first one is called latent heat of fusion. Since
fusion means the same as melting, it is a good de-
scriptive name. The other kind is called latent heat
of vaporization because‘ that means the same as
evaporation.
It may seem as though we have drifted into a story

9B-22 1973 OPEL SERVICE MANUAL
We can change a vapor back into a liquid by chilling
it, or do the same thing with pressure. When we
condense a vapor we will find that the heat removed
just exactly equals the amount of heat that was neces-
sary to make the substance vaporize in the first place.
At last the lost is found! The latent heat of vaporiza-
tion the heat that apparently disappeared when
a liquid boiled into a vapor again reappears on
the scene when that same vapor reverts back into a
liquid. It is just like putting air into a balloon to
expand it and then letting the same amount of air out
again to return the balloon to its original condition.
We know that any substance will condense at the
same temperature at which it boiled. This tempera-
ture point is a clear-cut division like a fence. On one
side, a substance is a liquid. Immediately on the
other side it is a vapor. Whichever way a substance
would go, from hot to cold or cold to hot, it will
change its character the moment it crosses over thefence.But pressure moves the fence! Water will boil at 212
degrees under normal conditions. Naturally, we ex-
pect steam to condense at the same temperature. But
whenever we put pressure on steam, it doesn’t! It will
condense at some temperature higher than 212 de-
grees. The greater the pressure, the higher the boiling
point and the temperature at which a vapor will
condense. This is the reason why pressure cookers
cook food faster, since the pressure on the water
permits it to boil out at a higher temperature. We
know that R-12 boils at 21.7 degrees below zero. A
thermometer will show us that the rising vapors,
even though they have soaked up lots of heat, are
only slightly warmer. But the vapors must be made
warmer than the room air if we expect heat to flow
out of them. Also, the condensing point temperature
must be above that of room air or else the vapors
won’t condense.This is where pressure comes to the rescue. With
pressure, we can compress the vapor, thereby con-
centrating the heat it contains. When we concentrate
heat in a vapor that way, we increase the intensity of
the heat or, in other words, we increase the tempera-ture;because temperature is merely a measurement
of heat intensity. And the most amazing part of it all
is that we’ve made the vapor hotter without actually
adding any additional quantity of heat (Fig.
9B-12).
Use of Pressure in RefrigerationBecause we must live by press&s and gauges in air
conditioning work, the following points are men-
tioned so that we will all be talking about the same
thing when we speak of pressures.
All pressure, regardless of how it is produced, is
measured in pounds per square inch (psi).Figure 98.12 Compressing a Vapor Concentrates its
HeatAtmospheric Pressure is pressure exerted in every
direction by the weight of the atmosphere. At higher
altitudes air is raritied and has less weight. At sea
level atmospheric pressure is 14.7 psi.
Any pressure less than atmospheric is known as a
partial vacuum or commonly called a vacuum. A
perfect vacuum or region of no pressure has never
been mechanically produced. Gauge pressure is used
in refrigeration work. Gauges are calibrated in
pounds (psi) of pressure and inches of Mercury for
vacuum. At sea level
“0” lbs. gauge pressure is
equivalent to 14.7 lbs. atmospheric pressure. Pres-
sure greater than atmospheric is measured in pounds
(psi) and pressure below atmospheric is measured in
inches of vacuum. The “0” on the gauge will always
correspond to the surrounding atmospheric pressure,
regardless of the elevation where the gauge is being
used.
Basic Refrigerator OperationWe’ve now covered all the ground-rules that apply to
refrigeration. Most likely they still are a little hazy,
but it is easy enough to remember these main points.
All liquids soak up lots of heat without getting any
warmer when they boil into a vapor, and, we can use
pressure to make the vapor condense back into a
liquid so it can be used over again. With just that
amount of knowledge, here is how we can build a
refrigerator.
We can place a flask of refrigerant in an ice-box. We
know it will boil at a very cold temperature and will
draw heat away from everything inside the cabinet
(Fig. 9B-13).
We can pipe the rising vapors outside the cabinet and
thus provide a way for carrying the heat out. Once

REFRIGERANT COMPONENTS ALL MODELS96.23Figure 96-l 3 Basic Refrigerant Circuit
we get the heat-laden vapor outside, we can com-
press it with a pump. With enough pressure, we can
squeeze the heat out of “cold” vapor even in a warm
room. An ordinary.radiator will help us get rid of
heat.
By removing the heat, and making the refrigerant
into a liquid, it becomes the same as it was before, So,
we can run another pipe back into the cabinet and
return the refrigerant to the flask to be used over
again.
That is the way most mechanical refrigerators work
today. Now, let’s look at an air conditioning unit to
see how closely it resembles the refrigerator we have
just described.
Basic Air ConditionerWhen we look at an air conditioning unit, we will
always find a set of coils or a tinned radiator core
through which the air to be cooled passes. This is
known as the “evaporator” (Fig.
9B-14). It does the
same job as the flask of refrigerant we
spok.e about
earlier. The refrigerant boils in the evaporator. In
boiling, of course, the refrigerant absorbs heat and
changes into a vapor. By piping this vapor outside
the car we can bodily carry out the heat that caused
its creation.
Once we get vapor out of the evaporator, all we haveFigure 98.14 Evaporator Assembly
to do is remove the heat it contains. Since heat is the
only thing that expanded the refrigerant from a liq-
uid to a vapor in the first place, removal of that same
heat will let the vapor condense into a liquid again.
Then we can return the liquid refrigerant to the
evaporator to be used over again.
Actually, the vapor coming out of the evaporator is
very cold. We know the liquid refrigerant boils at
temperatures considerably below freezing and that
the vapors arising from it are only a shade warmer
even though they do contain quantities of heat.
Consequently, we can’t expect to remove heat from
sub- freezing vapors by “cooling” them in air tem-
peratures that usually range between 60 and 100
degrees heat refuses to
flow from a cold object
toward a warmer object.
But with a pump, we can squeeze the heat-laden
vapor into a smaller space. And, when we compress
the vapor, we also concentrate the heat it contains.
In this way, we can make the vapor hotter without
adding any heat. Then we can cool it in compara-
tively warm air.
That is the only responsibility of a compressor in an
air conditioning system (Fig.
9B-15). It is not in-
tended to be a pump just for circulating the refriger-
ant. Rather, its job is to exert pressure for two
reasons. Pressure makes the vapor hot enough to
cool off in warm air. At the same time, the compres-
sor raises the refrigerant’s pressure above the con-
densing point at the temperature of the surrounding
air so it will condense.
As the refrigerant leaves the compressor, it is still a
vapor although it is now quite hot and ready to give
up the heat that is absorbed in the evaporator. One
of the easiest ways to help refrigerant vapor dis-
charge its heat is to send it through a radiator- like
contrivance known as a condenser (Fig. 9B-16).
The condenser really is a very simple device having
no moving parts. It does exactly the same job as the
radiator in a typical steam-heating system. There,
the steam is nothing more than water vapor. In pass-
ing through the radiator, the steam gives up its heat
and condenses back into water.
The same action takes place in an air conditioning

9B-24 1973 OPEL SERVICE MANUAL
Figure 9B-15 Compressor Assembly - GT Shown
Figure 3B-16 Condenser Assembly
condenser. The refrigerant vapor gives up its heat,
which is quickly and easily radiated into the sur-
rounding air through the large finned surfaces of the
condenser. In giving up its heat, the refrigerant vapor
condenses back into liquid which collects in a pool
at the bottom of the condenser.
As we have said before, when the refrigerant con-
denses into a liquid, it again is ready for boiling in the
evaporator. So, we can run a pipe from the condenser
back to the evaporator.
Main Units of the SystemThese three units then; the evaporator, the compres-
sor, and the condenser are the main working
parts of any typical air conditioning system. We have
the evaporator where the refrigerant boils andchanges into a vapor, absorbing heat as it does so. We
have the pump or compressor to put pressure on the
refrigerant so it can get rid of its heat. And we have
a condenser outside the car body to help discharge
the heat into the surrounding air.
Pressure and FlowThere is one more unit that co-operates with thesethree. It doesn’t do any real work, but it does act as
sort of a traffic officer in controlling the flow of the
refrigerant through the system. To get a better idea
of what this does. let’s first do a li,ttle exoerimentine
with an ordinary’ tire pump.
When we use a
t,ire pump to Sate an automobile
tire, we are creating pressure only because we are
“pushing” against the air already entrapped inside
the tire. If you question this, just try pumping up a
tire that has a large puncture in it. You could pump
all day, and still not be able to build up any pressure.
As fast as you would pump the air in, it would leak
out through the puncture.
Abou~t all you would be
doing would be circulating nice fresh air through the
tire.
1Jnless you have something lo push against - to
block the tlow of air
- you can’t create more than a
mere semblance of pressure.
The same situation holds true in an air conditioning
system. The compressor can pump refrigerant vapor
through the system, but unless it has something to
push against, it cannot build up pressure. All the
compressor would be doing would be to circulate the
vapor without increasing its
pres,sure.Yet we can’t just block the flow through the system
entirely. All we want to do is put pressure on the
refrigerant vapor so it will condense at normal tem-
peratures. What’s more, this
musi: be done some time
after the vapor leaves the evaporator and before it
returns again as a liquid. We can’t have high pressure
in the evaporator because that would slow down the
boiling of the refrigerant and thus penalize the re-
frigerating effect.
Controlling Pressure and FlowPressure and flow can be controlled with a float
valve, or with a pressure-regulating valve. They do
the same job, but in a different way.
Since the float valve type will give us a better idea of
pressure and flow control, let’s look at it first (Fig.
9B-17).It consists simply of a float that rides on the surface
of the liquid refrigerant. As the refrigerant liquid
boils and passes off as a vapor, naturally the liquid
level drops lower and lower. Correspondingly, the
float, because it rides on the surface of the refriger-
ant, also drops lower and lower as the liquid goes
down.By means of a simple system of mechanical linkage,
the downward movement of the float opens a valve
to let refrigerant in. The incoming liquid raises the
fluid level and, of course, the float rides up with it.
When the surface level of the refrigerant liquid re-
aches a desired height, the float: will have risen far

REFRIGERANT COMPONENTS ALL MODELS99.27that line, they still hadn’t gotten anywhere. So, they
started from scratch and juggled molecules around
to make an entirely new refrigerant. Eventually they
succeeded by remodeling the molecules in carbon
tetrachloride. This is the same fluid that is used in
fire extinguishers and dry-cleaners’ solvents.
From this fluid, the chemists removed two chlorine
atoms and replaced them with two fluorine atoms.
This newly-formed fluid carried the technical chemi-
cal name of dichlorodifluoromethane. Today, we
know it as Refrigerant-12 or R-12.
Fluorine is an extremely temperamental substance.
Under most conditions it is toxic and highly corro-
sive, and after is is manufactured, it has to be stored
in special containers because it will eat through glass
and will dissolve most metals in short order.
Despite its rambunctious character though, fluorine
is completely tamed when it is combined with the
other substances that go to make up the refrigerant.
Each is non-toxic, non-inflammable, non-explosive,
and non- poisonous; however, breathing large quan-
tities of R-12 should be avoided.
Pressure. Temperature Relationship of R-12A definite pressure and temperature relationship ex-
ists in the case of liquid refrigerants and their satu-
rated vapors. Increasing the temperature of a
substance causes it to expand. When the substance is
confined in a closed container, the increase in tem-
perature will be accompanied by an increase in pres-
sure, even though no mechanical device was used.
For every temperature, there will be a corresponding
pressure within the container of refrigerant. A table
of the temperature-pressure relationship of R-12 is
presented below. Pressures are indicated in gauge
pressure, either positive pressure (above atmos-
pheric) m pounds or negative pressure (below atmos-
pheric) in inches of vacuum.
“F-40
-35
i#Pressure
11.0*
8.3*
“F
50
50#Pressure
46.1
52.0
-30~
5.5*6057.7
-252.3*6s67 7__.
-200.6
io70.1
-152.4
76.9
-104.584.1
1;6.8 9.2tz99.6 91.71;
11.8 14.712116.9 108.1
1517.7105126.2
2021.1110136.0
2524.6115146.5
3028.5120157.1
;:
30.1
125167.5
32.6
131)179n
4037.0
4541.7*Inches of Vacuum.-. _.-
1402045
150232.0Thus if a gauge is attached to a container of R- 12 and
the room temperature is 70 degrees, the gauge will
register 70 psi pressure; in a 100 degrees room the
pressure will be 117
ps~
AIR CONDITIONINGBecause air conditioning has always been very
closely allied with mechanical refrigeration, most of
us are apt to think of it only as a process for cooling
room air.
But true air conditioning goes beyond the mere cool-
ing of the air. It controls the humidity, cleanliness,
and circulation of the air as well.
Whenever it gets warm and muggy in the summer-
time, someone is almost sure to say, “It’s not the heat
it’s the humidity.” But that is only partly right.
Actually it is a combination of the two that makes us
feel so warm temperature alone is not the only
thing that makes us uncomfortable.
Humidity is nothing more nor less that the moisture
content of the air. To a certain extent, it is tied in
with the temperature of the air. Warm air will hold
more moisture than will cold air. When air contains
all the moisture it can hold, we say it is saturated,
and the relative humidity is 100 percent. If the air
contains only half as much water as it could possibly
hold at any given temperature, we say that the rela-
tive humidity is 50 percent. If it contains only a fifth
of its maximum capacity, we say that the relative
humidity is 20 percent and so on. This amount
of water vapor, or relative humidity, affects the way
we perspire on hot days.
Nature has equipped our bodies with a network of
sweat glands that carry perspiration to the skin
sur-faces. Normally, this perspiration evaporates and, in
doing so, absorbs heat just like a refrigerant absorbs
heat when it is vaporized in a freezer. Most of the
heat thus absorbed is drawn from our bodies, giving
us a sensation of coolness. A drop of alcohol on the
back of your hand will demonstrate this principle
very convincingly. Because it is highly volatile, al-
cohol will evaporate very rapidly and absorb quite a
bit of heat in doing so, thereby making the spot on
your hand feel unusually cool.
The ease and rapidity with which evaporation takes
place, whether it be alcohol or perspiration, governs
our sensation of coolness and to a certain extent,
independently of the temperature. Of even more im-
portance, the ease and rapidity of the evaporation are
directly affected by the relative humidity or com-
parative dampness of the air. When the air is dry,
perspiration will evaporate quite readily. But when
the air contains a lot of moisture, perspiration will
evaporate more slowly; consequently less heat is car-
ried away from our body.