Electrical Bypass/On Demand Opening Of Liquid Refrigerant Solenoid Valves; Coil Replacement; Valve Disassembly; Valve Reassembly - PREVOST H3-41 Maintenance Manual

SECTION 22: HEATING AND AIR CONDITIONING
Low voltage: Check voltage across the coil
leads. Voltage must be at least 85% of
nameplate rating.
Excessive leakage:
clean all parts. Replace worn or damaged parts
with a complete repair kit for best results.
There are only three main possible malfunctions:
1. Coil burnout.
2. Failure to open.
3. Failure to close.
Each is discussed in Sporlan Parker Hannifin
Solenoid Valve Installation and Servicing bulletin
included on your Technical Publications USB
flash drive.
4.10.2 Electrical Bypass/On Demand Opening
Of Liquid Refrigerant Solenoid Valves
To ease purging, pumping down and refilling of
refrigerant, it is possible to open the liquid
solenoid valves (normally closed NC). To do so,
uncap and connect plug and socket housings of
connector C24 together for the passengers'
unit and overhead compartment units liquid
solenoid valves (located on the HVAC module
in evaporator compartment) or C44 for the
driver's unit liquid solenoid valve (located on
the ceiling of the spare wheel compartment).
During normal use, both plug and socket
housings of connector C24 or C44 are to be kept
unplugged and capped.
CAUTION
Connectors C24 & C44 must be disconnected
and their caps reinstalled after this procedure.
Leaving them connected will keep the driver's,
passengers and overhead compartment liquid
solenoid valves open, and result in battery
draining if the bus remains unused for several
days.
4.10.3

Coil Replacement

1. Unplug coil connector.
2. Take out the retaining screw at the top of the
coil housing. The entire coil assembly can
then be lifted off the enclosing tube.
3. Place the new coil on the enclosing tube.
Lay data identification plate in place.
38 PA1621 Maintenance Manual All Series | Revised February 2019
Disassemble valve and
4. Insert the coil retaining screw, rotate coil
housing to proper position and tighten screw
securely.
5. Plug coil connector.
4.10.4

Valve Disassembly

1. Because of possible damage to valve
components due to the high temperature of
soldering and brazing, it is necessary to
completely disassemble the A & B series
valves before any heat is applied to the
valve body. For E series (extended copper
connections), braze into the line without
disassembly because the valve contains
extended connections. Use caution by
placing a wet cloth or chill block on the
extensions at the body to prevent excessive
overheating.
2. Remove the coil as stated previously.
3. Pump down the system as stated in this
section.
4. Remove the enclosing tube and locknut, all
internal parts, and
assembly.
NOTE
The previous procedure must be followed
before brazing solder-type bodies into the line.
CAUTION
Be careful not to damage the machined faces
while the valve is apart.
4.10.5

Valve Reassembly

1. Place the seat disc into the valve body with
the smaller diameter end facing up.
2. Place the enclosing tube gasket onto the
valve body above the threads.
3. Hold the plunger with one hand so that the
pointed end is resting in the pilot port of the
disk. Make sure the small spring is in place
on the top of the plunger.
4. With the other hand, place the enclosing
tube over the plunger, making sure the
enclosing tube gasket is in position.
5. Put back the enclosing tube locknut and
tighten. Do not over tighten.
manual lift stem