Air Flow System

17

Air Distribution Systems (Continued)
Metal Air Distribution Assembly – Air Flow Logic

Note: A1 & A3 SHUTTER POSITIONS PROVIDE BLEED AIR TO DEFROST AND FLOOR OUTLETS RESPECTIVELY.

18

Air Flow System
Air Distribution Systems (Continued)
Metal Air Distribution Assembly – Shutter Logic

19

Air Flow System
Air Distribution Systems (Continued)
Plastic Form Molded Discharge Air Assembly - Air Flow Logic

Note: A1 & A3 SHUTTER POSITIONS PROVIDE BLEED AIR TO DEFROST AND FLOOR OUTLETS RESPECTIVELY.

20

Air Flow System
Air Distribution Systems (Continued)
Plastic Vacuum Form Molded/Metal Air Distribution Assembly – Shutter Logic

21

Air Flow System
Air Distribution Systems (Continued)
HVAC Base Unit – Shutter Logic

Thermostat
Relay
Part & Serial
Number Label

TXV &
Liquid Hose

Charge Label

Fresh Air Inlets

HVAC Base Unit
22

Electric
Actuator

Heating System
Safety Precautions & Warnings
SERVICING ENGINE COOLANT SYSTEMS:
1. Always wear the proper protective eyewear and clothing before working on any engine coolant
system. Remember, engine coolant systems can reach temperatures over 180⁰F. If coolant
gets in your eye, IMMEDIATELY flush eyes with running water for at least 15 minutes,
keeping eyelids open. Seek medical attention.
2. Always wear work gloves whenever you’re working with heating coils and hoses. The
aluminum edges are sharp, and can cause serious cuts.
3. Always stay clear of the belts and fan blade, and be careful revving the engine on a vehicle
with a flex fan – damaged blades have been known to come flying off without a moment’s
warning.

Warning:
NEVER remove the radiator cap on a vehicle while the engine is still hot or warm. Severe
scalding could occur.

23

Heating System
Engine Coolant System
ANTIFREEZE / COOLANT:
The main function of the Cooling System is to carry heat away from the engine and maintain the
desired operating temperature. This is accomplished by circulating antifreeze/coolant through the
engine, where heat is generated, and carrying it to the radiator to be cooled.
Modern recreational vehicles operate in a wide variety of ambient temperatures, from well below
freezing to well over 100 F. The fluid used to cool the engine must have a very low freezing point, a
high boiling point, and it must have the ability to transfer heat.
An adequate amount of an antifreeze/coolant and water mixture is necessary to reduce the
possibility of engine overheating and freezing, and contain additives to prevent rust and corrosion in
the cooling system.
Water is one of the most effective fluids for holding heat, but water freezes at too high a
temperature to be used in automobile engines alone.
The fluid used in most recreational vehicles is a mixture of water and ethylene glycol, also known as
"antifreeze" or "coolant". By adding antifreeze / coolant to water, the boiling and freezing points are
improved significantly.
The temperature of the coolant can sometimes reach 250 to 275 F (121 to 135 C). Even with
antifreeze added, these temperatures would boil the coolant. To prevent this, the cooling system is
pressurized, which further raises the boiling point of the coolant. Most systems have around 14 to
15 pounds per square inch (psi), which raises the boiling point approximately 45⁰F so the coolant
can endure the high temperatures produced in the engine.
ENGINE COOLANT HOSES:
The radiator hoses and heater hoses are easily accessed by opening the hood, at the engine
location, and inspecting. You want to be sure that the hoses show no visible signs of cracking or
splitting and that there is no bulging or swelling at the ends.
If there are any signs of problems, the hose should be replaced with the correct part number for the
year, make, model and engine of the vehicle.
Never use a universal hose unless it is an emergency and a proper molded hose is not available.
For either the radiator hoses or the heater hoses, make sure that you route the replacement hose in
the same way that the original hose was running. Position the hose away from any obstruction that
can possibly damage it and always use new hose clamps.
After the cooling system is refilled with the proper coolant mixture, a pressure test should be
performed to ensure that there are no leaks.

24

Heating System
Engine Coolant System (Continued)
BELTS:
On most older recreational vehicles, the water pump is driven by either a “V” belt or serpentine belt
on the front of the engine that is also responsible for driving the alternator, power steering pump and
air conditioner compressor. These types of belts are easy to inspect and replace if they are worn.
Check for dry cracking on the inside surface of the belt.
On newer vehicles, the water pump is often driven by the timing belt. This belt usually has a
specific life expectancy at which time it must be replaced to insure that it does not fail. Since the
timing belt is inside the engine and will require partial engine disassembly to inspect, it is very
important to replace the timing belt at the scheduled interval.

ITEMS OF CONCERN:







Check antifreeze/coolant level monthly. Only use a 50/50 solution of anti-freeze/coolant and
water.
Water quality plays an important role in protecting the cooling system. A high mineral content
may cause scaling or corrosion. De-ionized or distilled water should be used in 50/50 solution.
CAUTION: Do not remove the radiator pressure cap when the engine is HOT.
Inspect belts monthly. Replace belts that are worn, frayed or glazed. Adjust belts when more
than 1/2 inch can be depressed between the pulleys.
Belts with spring-loaded tensioners do not require manual adjustments.
Replace bulging, rotten, or brittle hoses and tighten hose clamps. If a hose looks bad or feels too
soft or too hard, it should be replaced.

25

Heating System
Diagnostics Guide
(Reference the appropriate electrical schematic first and follow “POSSIBLE
CAUSES” in sequence)
PROBLEM
1. Inadequate or No Heat.
(Discharge air only slightly
warm, or neutral).

POSSIBLE CAUSES

REMEDY

 Engine coolant
system’s fluid is low.

Check engine coolant level per
Chassis Manufacturer's
recommendation. Add Coolant as
required.

 Excessive air leaks
around the HVAC
base unit connection
to the fire wall or the
interior blower motor
assembly.

 Locate and seal leaks as required.

 Pinched heater
hose(s) or other
restrictions in the
engine coolant
system.

Repair
required.
 Examine
heaterif hoses
from the
engine cooling system to the heater
Core for pinches and kinks.

 Engine running cold.
Thermostat is stuck
open.

 Check engine coolant temperature
specifications according to the
chassis manufacturer’s
recommendations.

 Hot water valve isn’t
operating properly.

 Reference the “Hot Water Valve
Diagnostic Guide”.

26

Heating System
Hot Water Valve Diagnostic Guide
SYSTEMS CHECK:
Before attempting to troubleshoot, verify that the HVAC system (other than temperature
control) is operating correctly. With the vehicle running, test-operate the system and
check the following:
• Blower Motor is operating at all speeds.
• Ventilation Modes are all operating correctly.
• A/C system is operating correctly (engine-driven compressor, refrigeration system, etc.).
1. Attach refrigerant manifold gauge set to the Service Ports. Clamp the heater inlet and outlet
hoses to eliminate coolant flow through the heating valve.
2. Start the vehicle, set blower speed to high, depress the AC switch, rotate the temperature dial to
full cool (far left) and rotate the ventilation mode dial to Dash / Floor position.
3. Test the A/C performance according to the “A/C Systems Operation Check” and “Expected
A/C Performance Guidelines” located in the “Air Conditioning System Guidelines” section.
4. If the AC System isn’t operating correctly then reference the “Diagnostic Guide” in the “Air
Conditioning System Guidelines” section.
5. If the AC System is operating correctly then remove the heater hose clamps from the coolant
hoses. If a significant loss in cooling capacity in the A/C system occurs with noticeable rise in
discharge air temperature, after the clamps have been removed, then turn the vehicle’s ignition
switch off. This confirms flow of high temperature coolant through the water valve.
6. Carefully follow the step-by-step directions listed below for troubleshooting the coolant flow
control system. If a problem is found, repair and correct the fault before proceeding to the next
step.
7. When troubleshooting electric and/or electronic components, care must be taken to prevent
component damage while inspecting, using a test meter, light, etc. If questions or concerns
arise, during the troubleshooting process, then contact Evans Tempcon for telephone
assistance before proceeding any further. Refer to “Service” section for contact information.

27

Heating System
Hot Water Valve Diagnostic Guide (Continued)
COMPONENT TESTING:
1. The temperature controller is located in the center of the HVAC system control panel. Rotate
the potentiometer knob to verify smooth operation. The knob should rotate freely from the cool
stop (blue), to the warm stop (red). Do not force the knob to rotate past the cool or warm stops.
Doing so will cause irreparable damage to the potentiometer control. If the knob can be rotated
past the internal stop at the full cool and full heat positions, the potentiometer must be replaced
before any further valve diagnostics are done.
Locate the electronic coolant valve assembly near the Evans’ Heater-Evaporator base unit
(mounted on the dash sheet/bulkhead). The electrical connector is located on the top of the
actuator housing.
2. Verify that the port on the outlet side of the valve is connected to the inlet tube on
the heater coil. A flow direction indicator is located on the side of the valve to
help distinguish inlet and outlet ports. Also, the inlet side of the valve is always on the same
side as the harness connector. New valves also have tape wrapped around the inlet port that
clearly identifies the inlet port. The coolant supply hose from the engine connects to the inlet
side of the valve.
NOTE:
The electronic coolant valve is a "directional" valve, and must be correctly installed, or
it will not function properly. Coolant valves installed with the coolant flow reversed will leak
coolant past the valve cylinder resulting in poor A/C performance. Valves that have been
installed backwards should be replaced because seal damage could have occurred if the
coolant flow has been applied in the wrong direction.
CAUTION:
Removal of the coolant valve should be performed when the engine is cold.
Attempting to remove the valve when the engine is hot could result in burns and/or
serious injury due to extremely hot coolant escaping under pressure. Do not start the
engine while the coolant lines are disconnected as the engine will quickly pump the
system dry, which could result in damage to the engine.
3. Verify that the heater supply hose (connected to the coolant valve) is actually the hose coming
from the supply port on the engine. The supply port is usually on, or near the engine
thermostat housing. To positively identify the supply line, remove the valve from the coolant
lines and place both ends of the lines into a container to capture escaping fluid. Have an
assistant "turn over" the engine while you observe the coolant lines. The line that discharges
coolant when the engine is turned over is the supply line for the HVAC system.
NOTE:
This procedure will not be useful for systems with a bypass or “H” fitting. Correct plumbing will
have to be checked at “H” fitting in this case. Reference your chassis manual for systems with
“H” bypass fittings in the coolant lines.

28

Heating System
Hot Water Valve Diagnostic Guide (Continued)
ELECTRICAL TESTING:
1. Verify positive electrical connections at the coolant valve.
2. Unplug the wire harness connector from the coolant valve connector. Check the socket terminals
for damage. Inspect the pin terminals on the coolant valve connector for damage. If any pins in
the valve connector are loose or broken, replace the valve. Refer to the “Electrical
Schematics” for correct pin locations and wire colors.

TEMPERATURE CONTROL POTENTIOMETER:
1. Use a DC voltage test meter and find a good vehicle ground for the negative probe. Do not use
the negative connection on the wire harness.
2. Insert the positive probe from the meter into the black wire terminal on the wire harness valve
connector. The voltage value should always read 0 VDC because this is the ground connection
for the hot water valve. Refer to the “Expected Voltages – Matrix” for correct pin locations and
wire colors.
NOTE:
If voltage is detected on this circuit, then entire harness should be visually inspected for
damage, incomplete or misaligned connections. Do not proceed with testing until this voltage
bleed has been resolved.
3. Insert the positive probe from the meter into the red wire terminal of the wire harness valve
connector. The voltage value should always read near the vehicle’s regulated voltage. If not
then you have an issue with the wire harness or fuse.
NOTE:
Low system voltage could be the result of numerous causes and will cause the valve to fail to
operate. Do not proceed with testing until this voltage issue has been resolved.
4. Insert the positive probe, from the meter, into the yellow wire terminal of the wire harness valve
connector. Rotate the temperature control knob to the far left (BLUE) position. The voltage
value should always read near the vehicle’s regulated voltage when the potentiometer is in the
closed (BLUE) position.
5. Rotate the temperature control knob to the far right and measure the yellow wire connection.
The voltage value should always read 0 VDC when the potentiometer is in the open (RED)
position.
6. If the proper voltage readings are not measured at either valve position and all other electrical
issues have been resolved, then replace the temperature control potentiometer or controller if
needed.

29

Heating System
Hot Water Valve Diagnostic Guide (Continued)
ELECTRONIC VALVE ;
1. If the voltages readings at the valve connector are normal then carefully plug the connector into
the valve and then remove the HVAC control panel to access the temperature control
potentiometer connector.
2. Remove the connector from the potentiometer and install a jumper wire on the connector from
the red wire terminal to the yellow wire terminal. This will apply full vehicle voltage to the valve
and force the valve to fully close. Look into the valve coolant inlet port to visually verify that the
valve is completely closed.
3. Change the jumper from the red wire terminal to the black wire terminal so that the jumper
connects the yellow wire terminal to the black wire terminal. This will ground the control wire of
the actuator and the valve should be completely open. Visually verify again.
NOTE:
By nature of the design of the valve, when the coolant valve gate is fully open, half of the valve
port opening appears to be blocked. At no time will the valve port appear to be empty.
4. If the valve does not visually open or close completely, then replace it, attach the coolant hoses
and secure assembly for proper operation.
5. Proceed to “SYSTEM VERIFICATION TEST”, on the next page, to determine if repair is
complete. Keep in mind that, if heated coolant has traveled through the heater core prior to
these tests, then it will take several minutes before the core cools and proper valve operation
can be verified. Operating the A/C system for a few minutes will speed up the process of cooling
the heater core.

Hot Water Valve Assembly

30

Heating System
Hot Water Valve Diagnostic Guide (Continued)
SYSTEM VERIFICATION TEST:
1. Attach both coolant hoses to the correct valve ports, reinstall the control panel, and secure the
vehicle for operation.
2. Set the controller for high blower speed, and “Dash / Panel” ventilation mode.
3. Rotate the temperature control to full cool (BLUE - far left position).
4. Start the engine and set the engine speed to ~1500 rpm if possible. Remember to have the
vehicle transmission in Park or neutral gear and the parking brake ON.
5. Measure the Fresh Air inlet temperature and the dash vent air temperature, nearest to the unit
(passenger side dash louver), and record the values. Repeat these measurements at 5 minute
increments until the engine has reached normal operating temperatures.
6. If the inlet and outlet air temperature difference does not vary significantly as the engine warms
the coolant, then the valve can be considered completely closed. If the temperature difference
increases significantly, then the valve is leaking coolant through the heater core. Replace the
valve assembly.
7. Rotate the temperature control to full heat; an immediate and significant temperature change
should occur between the inlet and outlet temperature readings.
8. Rotate the temperature control back to full cool and monitor the temperature differential. The
change will be slower, but the outlet temperature should drop to where no significant difference
is detected between inlet and outlet temperatures. If the temperature difference does not
stabilize then the valve is leaking coolant through the heater core; replace the valve assembly.
9. Once the faulty component has been identified, the new replacement permanently installed, and
everything is buttoned back up, then perform an actual function test for warm and cool air with
the vehicle running. Test A/C performance using the “A/C Systems Operational Check” and
“Estimated A/C Performance Guidelines”.

31

Air Conditioning System
Safety Precautions & Warnings
SERVICING REFRIGERANT SYSTEMS:
1. Always wear the proper protective eyewear and clothing before working on any refrigeration
system. Remember, refrigerant in the air conditioning system can reach pressures of over 500
PSI – if one of those lines bursts while you’re working on the system, it can cause serious
injury. If refrigerant gets in your eye, it can freeze your eyeball, causing permanent damage or
blindness.
2. Always wear work gloves whenever you’re working with condensers or evaporators. The
aluminum edges are sharp, and can cause serious cuts.
3. Always stay clear of the belts and fan blade, and be careful revving the engine on a vehicle
with a flex fan – damaged blades have been known to come flying off without a moment’s
warning.
4. Always use a DOT-approved tank for storing used and recycled refrigerants. Look for the
Department of Transportation stamp: DOT 4BW or DOT 4BA.
5. Always provide plenty of ventilation when using any electrical testing, recycling or recovery
equipment. Avoid breathing any refrigerant vapor, lubricant vapor or mist. Exposure to these
(particularly PAG oil mist) may irritate your eyes, nose and throat.
6. Always follow the instructions for your recycling equipment; failure to follow those directions
could end up causing personal injury or damaging your equipment. Never perform any
maintenance or service on your recycling equipment while the unit is plugged in (unless
directed to do so) or without first consulting with authorized service personnel. Removing
internal fittings and filters can release pressurized refrigerant. Use care and always wear
appropriate safety wear.
7. Never use compressed air to leak test or pressure test an R-134a system or R-134a service
equipment. Under certain conditions, pressurized mixtures of R-134a and air can be
combustible. Always follow the proper procedures to prevent any safety hazards. In
addition, shop air injects moisture into the system, and a pressure surge could damage the
evaporator.
8. Microprocessors and computers are susceptible to damage from electrostatic discharge.
Always use a static strap when working with these components, and always take the
necessary precautions to prevent damage to electronic components.

Note:
To prevent cross contamination between refrigerants, verify that the A/C system has the correct
label and unique service fittings designed for R134a refrigerant. If you’re ever in doubt, check the
system with a refrigerant identifier.

32

Air Conditioning System
Diagnostic Guide
(Reference the appropriate electrical schematic first and follow “POSSIBLE
CAUSES” in sequence)
PROBLEM

POSSIBLE CAUSES

REMEDY

1. Inadequate Cooling
(Discharge air from
A/C vents is only
slightly cool.

 Leaking valve (Cooling
may be diminished at
engine idle. Increased
engine and
compressor speed will
improve A/C cooling).

 Refer to the “Electronic Valve
Troubleshooting guide”.

 Condenser clogged
with road debris or
Condenser Fan
inoperative.

 Examine fin region of the condenser for
debris and bent fins. Clean and
straighten as required. Repair and/or
replace the condenser fan components
as required.

 Incorrect refrigerant
charge in system. If
charge is excessively
low or high, the
compressor clutch will
not engage, or remain
engaged.

Install a manifold gage set onto high
side and low side service ports and
operate A/C. Observe for low
pressures. If low pressures are
observed, check all A/C components
for leaks as required. If excessive oil
loss is suspected, check oil level in
compressor, evacuate, and recharge.
Refer to the “Recommended R134a
Refrigerant Charge Charts”.

 Restriction in the TXV
resulting in a starved
evaporator.

 If low pressure readings are excessively
low and/or the liquid line at the expansion
valve is cool to the touch or showing
signs of sweating or frosting, then recover
the refrigerant. Evacuate and recharge
the system with the proper refrigerant
amount. Perform the “TXV Function
Test”. If symptoms repeat then replace
the TXV following the same service
procedure.

33

Air Conditioning System
Diagnostics Guide (Continued)
PROBLEM
POSSIBLE CAUSES
1. Inadequate Cooling  Restriction in
(continued)
receiver/drier resulting
in a starved
evaporator.

 Defective, worn or
leaking compressor.

2. Inadequate cooling  Excessive moisture in
during hot part of the
system which can
day.
cause the expansion
valve to frost and
restrict refrigerant flow.

REMEDY
 If low side readings are excessively low
and/or the liquid line at the expansion
valve is cool to the touch and showing
signs of sweating or frosting, discharge
then recover the refrigerant. Replace the
receiver-drier. Add 2 ounces of
recommended PAG oil, to replace oil
removed from the old receiver/drier.
Evacuate and recharge the system with
the proper refrigerant amount.
 Low side gauge reading too high and
high side gauge reading too low.
Recover refrigerant. Perform
“Compressor Function Test”.
Remove and replace new or rebuilt
compressor and replace receiver/drier.
Add 2 ounces of oil, to replace oil
removed with the old receiver/drier,
evacuate and recharge. (Check
compressor for factory oil charge)
 Recover refrigerant. Replace