MACS Monthly Newsletter - 2021 - JAN7

James Avery
James Avery

Figure 15: Graphic of Scan Tool cabin heater PID data available for a Gen 1 Chevrolet Volt.

Figure 16: Graphic of Scan Tool cabin heater PID data available for a Gen 2 Chevrolet Volt.

* A corresponding increase in heater hose temperature should
be observed a few minutes after commanding a higher temperature

* If current remains high during this test range or drops extremely low, this indicates a PTC that is failing. The failure mode is
dependent upon the PTC material and how the heater is controlled.
8. Once MAX temperature has been commanded, the Cabin Heater
should be loading full current:

* Max Current calculation:

* Cabin Heater kW/ HV Battery Pack Voltage = Maximum

Current

* Example: 6kW/360V = 16.66A

* If heat request is 50%, load current should be approximately

½ of full load current, etc. (this can help track load current in
general)
9. A 6kW PTC heater can heat the coolant to ≈200°F on MAX heat
10. Obviously, if the heater coolant pump is not operating, then coolant will not be circulated and a DTC will be logged (i.e., temperature
correlation faults, pump speed feedback Hz, no coolant flow through
reservoir, etc.).

Here is one simple process (this is a general process) for testing the
Cabin Heater, that should provide the concepts for how testing could
be performed:
1. Utilize HV Gloves & Safety Glasses when connecting to the HV
system
2. Connect Scan Tool to monitor Cabin Heater PIDs (if available) and
DTCs
3. Place DC Current clamp around one of the Cabin Heater HV power
cables
4. Connect DC Current clamp to an oscilloscope
5. While recording Cabin Heater Current (Amperage) with the oscilloscope, Power vehicle ON and place Cabin Heater at lowest temperature setting on the instrument controls. When first powered, the oscilloscope may record a Current Ramping for the first 20 - 40 seconds
before the current reaches maximum current for the temp setting.
6. If no load current is present, don't forget to check the Cabin Heater
HV Fuse (service information)
7. At 3 to 5-minute intervals, increase cabin temperature on the instrument controls and check heater hose temperatures (thermal imager)
or duct outlet temperature (digital thermometer) for corresponding
temperature increases, while checking for corresponding increases
in load current. When incrementally increasing the temperatures, observe the oscilloscope (or recording).

* A sharp increase in Current for the first few seconds may be
observed, due to the PTC heaters starting the heating process (see
previous paragraph about PTCs and the NTC operational region)

January 2021

Note: Most OEMs will not provide the kW rating of the Cabin
Heater. The Cabin Heater will have a label on it with a part number
(and possibly the manufacturer name). A quick internet search on
the manufacturer or part number will usually provide technical
data sheets or manufacturer tech support contact information to
acquire the kW and some fundamental operational information.

MACS Service Reports

MACS Monthly Newsletter - 2021

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