Proheat X45–School Bus - Manual (Page 75)

PROHEAT INSTALLATION & SERVICE 5-18
A VOLTAGE diagnostic code indicates that the supply voltage to the heater is
out of the normal operating range.
Voltage ranges:
12 Volt heater – 10.0 to 15.0 Volts
24 Volt heater – 20.0 to 30.0 Volts
Check: Vehicle Voltage
a) Heater voltage must be within the specified range. See
following page for procedure to measure heater voltage.
NOTE: Bad connections may show good voltage under no load conditions
but not under full load. With the heater “OFF,” measure the voltage.
Then switch the heater “ON” and measure the voltage again. If
the voltage drop is more than one Volt, check the vehicle battery
connections, harness and the power connection at the PCM.
b) If the measured voltage is higher than the specified range
then check the voltage regulator on the vehicle.
NOTE: If the vehicle batteries are marginal, starting the vehicle while the
heater is running may:
a) Drop the voltage enough to cause a voltage error.
b) Cause random component errors (brown out).
To reset the PCM, switch the heater “OFF” and then back “ON” at the dash
ON/OFF Switch. If the problem continues, load test the batteries to confirm their
condition. Each battery should be independently tested.
Current: Checking current draw is done at the power harness connections
on the batteries.
1) Check current draw on the red POSITIVE wire with the heater
NOT running. Should read 50 to 100 mA.
2) Check current draw on the red POSITIVE wire with the heater
running in full output, ignition “OFF.” For 12 V models, the
current should be 6.5 to 9.0 A (varies with input voltage). For
24 V models, the current should be 2.0 to 6.0 A (varies with
input voltage).
3) Check current draw on the black NEGATIVE wire with the
heater NOT running and the red POSITIVE wire disconnected.
Should read 0 mA. This test is to confirm whether or not
there is a power leakage from the vehicle through the heater.
Heater Voltage Measurement
The positive terminal of the ignition coil is always hot relative to the heater
chassis ground as long as power is connected to the heater. This is the
supply voltage to the heater.
Test Procedure:
a) Locate the rubber boot on the end of the ignition coil and
peel it back to expose the positive and negative terminals.
b) Select the DC Volts range of a multimeter and connect as
per Figure 5-17. The positive lead of the multimeter should
be attached to the positive coil lead. The negative lead of the
multimeter should be attached to the heater chassis at the
PROHEAT ground boss. (Figure 5-17)
c) Read the voltage with the heater running or trying to run.
Normal Voltage Ranges
12 Volt heater – 10.0 to 15.0 Volts
24 Volt heater – 20.0 to 30.0 Volts
5 Voltage