10. Pressure
Compensation under
Diaphragm
11. Metallic Diaphragm
12. Sensing Element

TXV - Closed
9.
F
1

11.
10.
F2

12.

3.

4.

1.

2.

5.
6.

62

9.
F
1

11.

7.
F
3

8.

High
Pressure
Liquid

Air Conditioning System Components
Thermostatic Switch
An evaporator normally removes the moisture or dehumidifies the air entering the HVAC
unit and condensate develops on the surfaces of the cooling coil. This condensate runs
down that surface to a collector pan, and is drained away.
In some cases due to low ambient temperature, high humidity air entering the HVAC unit,
low refrigerant charge or no air flow, the condensate can begin to freeze on the
evaporator.
An air conditioning system will not operate properly and will lose cooling capacity if the
evaporator coil becomes blocked with frost or ice. The cool air flowing out of the system
will be reduced as the ice area continues to grow.
When liquid refrigerant enters the evaporator coil, temperatures may be as low as 10 ⁰F
at that point - that is at the point of refrigerant entry to the evaporator. In normal operation
of a refrigeration system, air movement across the evaporator coil provides enough
warmth that frost or ice doesn’t form on the coil.
The evaporator thermostat’s function is too sense the coil’s surface temperature and
disengage the compressor’s clutch should the temperature fall below the freezing point of
moisture or 32⁰F/0⁰C.

Probe
Location

Evaporator Thermostat

HVAC Base Unit Location

63

Air Conditioning System Components
Condensers
The Condenser function is to act as a heat exchanger and allow heat to flow from the hot
refrigerant to the cooler outside air.
R134a entering the condenser will be a high-pressure high temperature vapor. As the
R134a vapor travels through the tubes of the condenser heat is given off to the cooler
ambient air; the refrigerant vapor condenses and changes to a liquid state.
At this point a large amount of heat is given off by the R134a. The refrigerant will now be a
hot, high pressure liquid.

Design types
Serpentine
This type of condenser consists of one long tube which is coiled over and back on itself with
cooling fins in between the tubes.
Parallel flow design
(Recommended for R134a)
This design is very similar to a cross flow radiator. Instead of refrigerant travelling through
one passage (like serpentine type), it can now travel across numerous passages. This will
give larger surface area for the cooler ambient air to contact.

Serpetintine Flow

Parallel Flow

IN High Pressure
Vapor From
Compressor

OUT High Pressure
Liquid to filter Drier

Baffles

Heat given off from
Refrigerant to
cooler surrounding
air

64

IN High Pressure
Vapor From
Compressor

Air Conditioning System Components
Foam Seals
These seals are fitted in between the
condenser and radiator to prevent the heated
ambient air exiting above, below or to the
sides of the space in between (normally
25mm) the radiator and condenser.

Without Foam Seals

As ambient air is drawn through condenser by
the condenser or radiator fan, its temperature
increases. If gaps are present between the
condenser and radiator this heated air can be
circulated back through the condenser. This
results in the increased condenser
temperature and causes reduction in the
performances of the A/C system.

Condenser electric fan
Fan Types

Most vehicles with air conditioning require an
electric fan to assist air flow, either pushing or
pulling the air through the condenser,
depending on which side of the condenser
the fan is placed.
The majority of vehicles using R134a require this
additional condenser cooling due to the higher
operating pressures of R134a. Also most modern
vehicles now have smaller grilles or bumper bar
openings. This causes poor air flow conditions
especially by the amount of air flow over the
condenser.

Conventiona
l Paddle

Skew
(By reversing the fan
blades it can either
push or pull the air)

Basic Circuit
The condenser fan is operated with A/C
engaged in various ways:

Compressor

- Medium pressure switch;
- Indirect connection to the compressor clutch
- Via the Electronic Control Module (ECM);
- Signal from the A/C switch activation.

30Amp Relay
Power to
Compressor

Fuse 25 Amp

65

Air Conditioning System Components
Receiver/Driers
Receiver/Driers are usually located on the high
side of the A/C system before the expansion
valve. The receiver/drier “receives” liquid
refrigerant from the condenser, stores it, filters
out contaminants from the A/C system, and
removes moisture. A/C systems using a
receiver/drier use an expansion valve to control
the refrigerant flow.
From the condenser, the refrigerant makes its
way to the receiver/drier. The receiver/drier
contains a desiccant to remove excess moisture
away from the refrigerant.
The receiver/drier also stores additional
refrigerant until it’s needed later when the heat
loads increase. The heat load is the amount of
heat to be removed from the air. A number of
variables affect heat load: ambient temperature,
the number of passengers, hydraulic component
heat, solar heat, and/or engine heat. As heat
loads increase, the need for extra refrigerant
increases with it. That extra refrigerant is stored
in the receiver/drier.
From the receiver/drier, the high-pressure liquid
refrigerant makes its way back to the expansion
valve to begin its journey all over again.
Most R134a receiver/driers have NO sight glass.
This is because the PAG oil will foam giving a
false impression of low gas charge. If the
receiver/drier does utilize a sight glass then
ensure correct diagnosis when viewing.

66

Air Conditioning System Components
Refrigerant Pressure Switches
1. Low refrigerant pressure switch – prevents the suction or low side of the
refrigerant circuit from going into a vacuum and potentially harming the
compressor.
2. High refrigerant pressure switch - 3 typical types:
A. Single – one fault setting.
B. Binary – two fault settings.
C. Trinary – three fault settings.
3. High refrigerant pressure switch typical functions are:
A. Low refrigerant charge protection.
B. Condenser fan control by energizing condenser fan relay at a predetermined
high pressure setting.
C. Compressor protection by de-energizing the compressor clutch at a very high
pressure setting.
Trinary Switch Example

67

Air Conditioning System Components
Refrigerant Hoses
OWING TO THE SMALLER
MOLECULAR SIZE AND
HIGHER OPERATING
PRESSURES OF R134a, the
refrigerant hose now
incorporates a nylon inner
lining. This is to reduce the
normal refrigerant leakage that
would naturally occur through
the porosity of rubber hoses,
called permeation.
.

Rubber

Rubber
Nitrile

Reinforcement

Most R134a hoses have a
smaller outside diameter and
thinner hose walls to improve
flexibility and reduce noise
levels within the A/C system.

Nylon

O-Rings & Fittings
The "O" ring rubber compound used for R134a A/C system joints, fittings and components is a
Hydrogenated Nitrile Butadiene Rubber (HNBR) and identified by the color green.
"O" ring lubrication can be carried out using mineral oil. Other manufacturers could use "O" rings
of a different color and size. Ensure that only the approved "O" ring is used for the type of system
being serviced or repaired.
Replace “O” ring on every fitting that has been disconnected. Use only HNBR “O” rings
for replacement.

R134a - R12 Comparison
- R12 “O” rings’ color is black
- NEVER use R12 “O” rings with R134a as the “O” ring will be damaged
because of the lack of chlorine in R134a
- You can use R134a “O” rings in an R12 system
- NEVER use PAG oil to lubricate o-rings, as it is highly hygroscopic, retaining
moisture that can contribute to fitting corrosion. Use Mineral Oil to lubricate o-rings.

68

Air Conditioning System Components
O-Rings & Fittings (Continued)
The following is a general list of recommended torque values for standard O-ring fittings for
reference during service operations.
Always use specific torque values on installation instructions over these general values.
HOSE FITTING CONNECTIONS -- RECOMMENDED TORQUE VALUE
Fitting Size*

Thread Size

Torque Value (lb-ft)

#6
#8
#10
#12

5/8 – 18
3/4 - 16 or 18
7/8 - 14 or 18
11/16 - 14 or 16

11 to 13
15 to 18
18 to 22
24 to 28

*Do not judge fitting size by the size of the hose. Many times they will not be the same.
COMPRESSOR FITTINGS AND SERVICE VALUES
Type
3-Way Service Valve to Compressor Fitting
Compressor, Sanden Seltec (Zexel)

Thread Size
1 -14
3/4 – 16
7/8 – 14

Torque Value (lb-ft)
20 - 40
18 - 22
18 - 22

HOSE TO METAL COMPRESSION FITTING
See specific instructions for this type fitting.
- PAG oil is highly hygroscopic. Mineral oil is recommended for O-Ring Lubrication.
Example of an O-Ring that has experienced excessive torque

69

EVANS TEMPCON
DASH HEATER A/C
All Electric Control
Systems

Owner’s Manual
Operating Instructions
For additional owner and operator
information visit us on the web at

www.evanstempcon.com

WARNING
This heater / air conditioner should be serviced by a fully trained and
environmentally licensed technician. Failure to do the above could result in
serious injuries, fines, and possible voiding of any warranties.

RV012682

70

LIMITED WARRANTY
MOTOR HOME DASH HEATER AND
AIR CONDITIONER SYSTEMS

EVANS Motor Home Dash Heater/Air Conditioners are warranted against defects in material and
workmanship to the original end user. Please consult the Motor home manufacturer for warranty
and service information. During the duration of the warranty, EVANS, will at its option, repair or
replace any part which, upon examination by EVANS or an authorized service provider of
EVANS, is found to be originally defective. A list of authorized service providers can be found at
www.evanstempcon.com.
CALCULATION OF WARRANTY PERIOD
The warranty period for an EVANS product installed as original equipment shall begin on the
date of the original purchase by the end user of the product in which it is installed. The end user
may be required to provide proof of the original delivery.
EXCEPTIONS AND EXCLUSIONS
To the extent that any or all of the following exclusions are prohibited by the law of any state or
municipality and cannot be pre-empted, they shall not be applicable.
1) There are no other express warranties, except as set out above, and any implied warranties
are limited in duration to that of the express warranty.
2) THERE IS NO WARRANTY COVERING CONSEQUENTIAL DAMAGES, INCIDENTAL
DAMAGES OR INCIDENTAL EXPENSES, INCLUDING DAMAGE TO PROPERTY.
3) There is no warranty covering damages caused by failure to perform normal and routine
maintenance as set out in the operation and service instructions.
4) There is no warranty covering damages caused by mishandling, neglect, lightning, corrosive
atmosphere, improper installation, or improper power supply.
5) The warranty shall be void if nameplate is removed or defaced.

701 Ann Street N.W.
Grand Rapids, MI. 49504
Telephone (616) 361-2681
Fax (616) 361-9646
www.evanstempcon.com

71

DASH HEATER / AIR CONDITIONER
Your new motor home has been equipped with the industry's highest performance integrated
heating and air conditioning system. It is not designed to cool or heat the entire motor home.
This system is designed to provide windshield defrost, heating and cooling for the front seat
occupants only. By following the operating instructions and tips, this heater / air conditioner will
provide many years of comfort and dependable service.
System Layout
The heater / air conditioner unit is located beneath the dash of the vehicle with heating and
cooling coils located on the outside of the firewall. In all modes of operation the unit takes fresh
air from outside, and heats or cools it before discharging into the vehicle. Only when operated in
the RECIRC AIR mode does the system take air from the inside of the vehicle.

TYPICAL DASH A/C SYSTEM
The type and location of the air discharge outlets can be different in each model motor home.
Consult your dealer on the location and operation of the air outlets on your motor home. Proper
adjustment of air outlets will provide maximum comfort.

72

CONTROL PANEL OPERATION
The control panel enables the driver to control the temperature, volume, and direction of the air
discharged from the heating/air conditioning system.

TYPICAL CONTROL PANEL

Blower Control
One of the best ways of controlling temperature is by changing the speed of the blower. The
blower switch controls the system on/off and provides up to 4 speeds in any mode.

Temperature Control
The temperature control dial controls only the heat content of the discharge air. The
temperature control dial will also control the overall temperature of the discharge air if the AC
system is operating. Turn the knob to the right (red area) for warmer air, and to the left (blue
area) for cooler air. Use of the temperature control will also moderate the discharge temperature
when the cooling system is engaged.

AC Switch
Engages cooling system. The switch will be inactive unless the blower is set on any position
other than off (0) to protect the system from forming ice on the core that would block air flow.
AC will function in any discharge air mode.

Recirculated Air Switch
Your driver/passenger heater and air conditioning system is designed to operate in fresh air
mode by default. The recirculating air feature is primarily used for faster passenger area cool
downs during the summer and warm ups during the winter by closing off the fresh air source and
recirculating the passenger compartment air. Pressing this switch will place your system in the
recirculated air mode.
Note: Prolonged use of this feature can cause stale air quality and moisture to form on the
windows.

73

AIR DISTRIBUTION - MODE CONTROL
To achieve the maximum comfort in your motor home, the air must be directed where it is
needed. The mode switch (right of center) gives the driver the ability to select where the air will
flow.
PANEL MODE – Air is drawn into the system and discharged though the dash
louvers only.

BI-LEVEL – Air is drawn into the system and discharged through the dash louvers
and floor outlets.

FLOOR – Air is drawn into the system and discharged through the floor outlets.

MIX – Air is drawn into the system and discharged through the floor and defrost
outlets.

DEFROST – Air is drawn into the system and discharged through the defrost
outlets.

OPERATING FEATURES
The air conditioning system is designed to operate in all air distribution modes. This provides
significant moisture, dust and pollen removal for enhanced passenger comfort.
The EVANS vehicle air conditioning system will not function if the outside air temperature is
below approximately 40o F. For cool air circulation during low temperatures, it is suggested the
operator utilize FRESH AIR mode.

74

IMPORTANT OPERATING FEATURES AND TIPS
Window Fogging
In mild, but rainy or humid weather, windows may fog on the inside. To clear the fog of all driver
area windows, turn on the air conditioning, set the system air intake to RECIRULATION AIR by
engaging the RECIRC button, adjust the temperature and fan control to maintain comfort,
position the mode control to DEFROST.
Winter Operation





Remove snow and ice from windshields and system air intakes if applicable.
The discharge air will heat up faster if the blower is operated on lower speeds until the
engine is hot and the RECIRC switch engaged (illuminated)
For windshield de-icing, use DEFROST mode.
Insure the air intake is free of ice and slush.

Summer Operation
Air-conditioned vehicles must be protected with a high-quality antifreeze coolant during summer
to provide corrosion protection and to raise the boiling point of the coolant for protection against
overheating. A 50% concentration is recommended.




Use Recirculated air control for a quick cool down.
Close all windows and vents to hot humid outside air.
Close all curtains which do not obstruct the driver's vision.

CARE AND SERVICE





Keep the condenser and radiator free of bugs and debris.
During periods of little use, operate the A/C system monthly to keep the compressor and
seals lubricated.
Periodically inspect the belts and hoses for wear and proper tension.
Periodically check for proper coolant levels.

WARRANTY / SERVICE
WARNING:
THE AIR CONDITIONING SYSTEM CONTAINS REFRIGERANT 134a UNDER HIGH
PRESSURE AND SHOULD BE SERVICED BY QUALIFIED PERSONNEL ONLY.
REPAIRS THAT ALTER THE DESIGN OF THE EVANS SYSTEM INCLUDING USE OF NONEVANS SUPPLIED PARTS WILL VOID THE WARRANTY AND ANY EVANS LIABILITY FOR
THE SYSTEM.
If repairs are required contact your dealer or motor home manufacturer for warranty period and
details. If traveling and service is required, you can contact your motor home manufacturer for
the nearest dealer, or contact Evans by phone or through our web site to find the nearest Evans
Service Center.

75

EVANS ALL ELECTRIC CONTROL PANELS

76