Page
19 of 40
Number
PM820010
HVAC: SmartAir eHVAC System
connection, high pressure situation or defective switch. If
the pressure, harness and connections are okay, the
EHVAC unit will have to be replaced.
E. Check Continuity Across Fuse Body
Fuse does not look blown.
Remove fuse from fuse holder. Using a meter, check for
continuity across the fuse. You can check for voltage at
and through the fuse using a DC volt meter, with the fuse
installed.
F. Discharge Temperature Sensor/Freeze
Switch Testing
Location: Between evaporator coil and intake side of
blower.
The freeze switch is a temperature sensor. To verify the
condition you will need a Volt/OHM meter.
If a freeze condition occurs, the unit will stop the com-
pressor. If the freeze condition leaves, the compressor
will restart and the unit will continue to run.
Check resistance (ohms) value at the system controller
with the 32 pin connector disconnected. You should read
a resistance across terminals D3 (pos) and D5 (neg)
within the range listed on the “
” on page 27. If you cannot
read the resistance, check at the sensor connection. If
you read the resistance here, and it's within the range
allowed, you have a defective harness.
If you cannot read the resistance or it is not within the
given range, your sensor is defective.
G. Compressor Thermal Limit Switch
You must remove the top cover and the plastic shield on
top of the compressor, to access the switch.
This device is a normally closed switch. If the compressor
gets too hot, the thermal limit switch will open and the
compressor will stop. Checking with a meter you should
always have continuity between the two terminals when it
is cool.
H. Main Controller/Compressor Controller
See updated information on “
Terminal / Controller and Compressor
You must remove the cover.
Do not attempt to test the controller or compressor until
you have completely eliminated all other possibilities.
Overview
When you turn the Peterbilt EHVAC unit on, if all safeties
are okay, such as the high pressure switch, temperature
sensor / freeze switch and the compressor thermal limit
switch, the Main / Compressor controller will connect the
compressor relay, condenser fan relay and the evapora-
tor blower relay terminals 86 to ground at their respective
terminals D10, D11 and D12 at the controller. This will
close the contacts 30 and 87 of all 3 relays and allow
power to each component. The compressor and evapo-
rator blower will begin to operate at a speed determined
by the manual control panel. The condenser fan will run
at normal operational speed.
Initial start up, the system defaults to Auto Mode, Blower
speed 1 and 60°F set point. After the settings are
changed for the first time, they will always default to the
last setting.
Use the following steps to check the controller:
a. With the control switch off – check for 12 VOLT
from F1 10 amp fuse to the back of the control.
b. Now check for 12 volts at switch terminal 6 (wake
up) coming from the main/ compressor controller
terminal D6. Turning the unit on will switch this
12 volt input from the main controller to ground at
the control panel. This signals the main control to
start the system.
c. With a correct 12 volt signals to and from the
control, now check for (ground) signals to relays
on D10, 11 and 12. All relays should be closed
and all terminals # 87 should have 12 volts. If you
lose any signals from the controller it must be
replaced.
d. With relays closed, the main controller will now
signal each component to start. The evaporator
blower receives its power from the linear power
module. Safety controls must be in a normal
state for the above signal to operate the unit.
