The document discusses the unique heating and cooling systems used in hybrid vehicles. It notes that hybrids use electric coolant pumps, coolant storage tanks, and supplemental electric heaters to quickly warm the engine during startups and provide heat when the engine is off. Hybrid air conditioning systems use electric compressors to operate without the engine running. The systems require special oils and procedures due to their high-voltage components.

1. Hybrid Heating and
Air Conditioning

2. Hybrid Heating and A/C
• Cooling and heating systems in hybrid vehicles operate
on the same principles as conventional vehicles but have
unique operating parameters.
• We are going to take a look at these unique differences.

3. Cooling System
• The purpose of the ICE cooling system is to bring the ICE
up to an optimum temperature as soon as possible and
keep it there under all conditions.
• We keep the ICE temperature in a narrow range for a
number of reasons, such as;

4. Cooling System
1. ICE performs at its highest efficiency and lowest
emissions at operating temperature.
2. Vehicle drivability is enhanced.
3. Cold engines wear out faster.
4. Used to heat the passenger compartment.
5. Overheated engines reduce efficiency and may fail.

5. Cooling System
• All automotive ICE’s use a liquid coolant that is
circulated by a water pump (usually mechanical) through
the water jackets, into the heater core, and after warm up
(opened thermostat), through the radiator.
• Turns on a fan for circulation if A/C is on, ICE is
overheating, and or ECT is increasing.

6. Cooling System
• We are all familiar with this process and these
components:
1. Thermostat
2. Pressure Cap
3. Coolant Tank
4. Water pump (Mechanical or Electrical)
5. Coolant (Inorganic Additive Technology (IAT/Silicate,
Organic Acid Technology (OAT), & Hybrid OAT)

7. Cooling System
What happens to this conventional system when our
hybrid enters idle-stop?
Are there ways to speed up the warm up process and keep
the ICE at operating temperature more efficiently?
How do you heat up the passenger compartment in EV
mode?
Lets talk about some unique components utilized in hybrid
vehicles to overcome some of these issues?

8. Cooling System
• Cold engines condense fuel on manifold and cylinder
walls, requiring a richer air-fuel ratio.
• Prius vehicles up to 2003 used an HC adsorber to reduce
start up emissions.
• With increasing emission standards, the 2004-2009
Toyota Prius (2nd Gen) utilizes a coolant storage tank to
bring engine temperature up quickly and supply heated
coolant to the passenger compartment heater core. Here’s
how;

9. Cooling/Heating Systems
• Prius vehicles up to 2003 used an HC adsorber in its
catalytic converter to reduce emissions on start up.

10. Cooling/Heating System
• On 2004-2009 Prius vehicles, the storage tank is built
much like a thermos with a vacuum layer between the
casings, holding just under a gallon of coolant.
• Coolant can be kept hot for up to three days!

11. Cooling/Heating System

12. Cooling/Heating System
• The system uses a water valve that directs coolant flow
between the tank, ICE, and heater core.
• There are four modes of operation;
1. Preheat
2. Engine Warm-Up
3. Storage During Driving
4. Storage During Ignition Off

13. Preheat
• Enabled prior to ICE start up, the ECM turns on an
electric water pump on the storage tank, sending hot
coolant from the tank to the ICE head assembly.
• After the preheat cycle is complete the ICE is allowed to
start and the next mode is entered.

14. Engine Warm-UP
• Storage water pump is turned off and the water valve
directs coolant from ICE into the heater core.
• Coolant is bypassing the storage tank until operating
temperature is achieved.

15. Storage During Driving
• Once the ICE is at operating temperature the water valve
is moved to allow fresh coolant to flow into both the
heater core and the storage tank, replacing the existing
coolant.

16. Storage During Ignition Off
• If the ICE is shut off before the tank is filled, an electric
water pump is turned on to finish filling the tank.
• Only happens if ICE is turned off at operating
temperature and the storage tank has not been purged.

17. Cooling/Heating System
• 2010 and newer Prius, removed the storage tank in favor
of a exhaust recirculation heating unit.

18. Servicing Parts
• If you are going to remove any of
these parts, its crucial to lose as
little coolant as possible, to
prevent air pockets.
• To refill these systems you must
use a scan tool (turn on electric
motor, and operate valves), along
with opening bleeder parts, and
using a coolant vacuum refill
tool.

19. Servicing Parts

20. Servicing Parts
There can be several bleed points, in various places. Always
follow service procedures.
To drain the coolant you may need to open bleeders and use
a scan tool to run the valves and electric water pump.

21. Diagnostic Tip!
• Just like how we used an infrared gun to see if the
catalytic converter is working (temp increase), we can
determine the health of a radiator (even temp decrease),
and when a thermostat opens, using the same infrared
gun.
OBD1 TIP! Use an
infrared gun to
determine which cylinder
has a misfire…measure
temperature outlets in
exhaust manifold!
TIP! Use an infrared gun to
diagnose heater
problems… measure heater
core inlet and outlet!

22. Cabin Heating System
• Conditioned air enters the plenum either from fresh air,
or recirculated air, and is directed through the
evaporator, and either through or around the heater core.
• After the air is conditioned to the desired temperature, it
is routed through mode doors to its final destination.

23. Cabin Heating Systems

24. Cabin Heating Systems
• Because of Idle-Stop, and higher
efficient ICE’s. The need for a
supplemental heating device is
required in hybrids.
• Electric PTC (Positive Temperature
Coefficient) heaters are being used
to accommodate this need.

25. Cabin Heating Systems

26. Cabin Heating Systems
• Another device to help “Boost”
the heating capability is a PTC
heater in the footwell air ducts.
• These Honeycomb electric
heater grids, help heat the
passenger compartment when
coolant temperature is low.

27. Cabin Heating Systems
• Ford uses a PTC heater for both supplemental
compartment heating, and warming up the coolant for
the ICE.

28. Cabin Heating Systems

29. Cabin Heating Systems
• Some cars utilize a different system to heat the cabin,
called a heat-pump. It works like an A/C system, but
backwards. This style system uses less battery energy,
increasing vehicle efficiency.

30. Cabin Heating System
• The draw back is, this system
doesn’t work as well when its
REAL cold outside, since it is
using the ambient atmosphere
heat.

31. Electronics Cooling
• A special cooling system is
needed for the hybrid
electronics/traction motors,
because it operates at a lower
temperature than the ICE and
needs to be contaminate free.

32. Electronics Cooling
• Some vehicle have several separate cooling systems. Each
loop has its own reservoir, electric water pump, and
maybe a filter.

33. Electronics Cooling
• Since these systems use an electric pump, there is no
need for a thermostat. The pump is cycled on and off at
different speeds, to accommodate coolant temperature.

34. Electronics Cooling
• Some vehicles use one reservoir, and a series of valves
and electric pumps to control different “loops”. Most
hybrids use the same coolant in the electronics cooling as
the ICE.

35. Electronics Cooling

36. Electronics Cooling
• Some vehicles like the Honda IMA don’t use a liquid
coolant, but are air-cooled.

37. A/C Systems
• We all know that refrigerant systems work by changing
state, and absorbing heat in the passenger compartment
(evaporator), but there are unique differences in hybrids.

38. A/C Systems

39. A/C Systems
TXV FOT

40. A/C Systems

41. A/C Systems
• Conventional A/C systems
pump the refrigerant with
a belt driven compressor,
and an electric clutch to
control operation.

42. A/C Systems
How would this be effected by idle-stop?
When the ICE shuts off, so does the A/C!

43. A/C Systems
NOTE: On early Prius vehicles (up to 03), and Honda
IMA’s, the ICE will not enter idle-stop if the A/C is on.
(Belt driven compressor)

44. A/C Systems
So how do we have A/C with the ICE off?
ELECTRIC COMPRESSOR!

45. A/C Systems
• Hybrid vehicles use a “Scroll” type compressor, since it is
more efficient (no pistons).
• The downside is it doesn’t handle high load (hot summer
day) as well…..

46. A/C Systems

47. A/C Systems
• Since we can control the speed precisely with an inverter
and control module, we no longer need to turn it on and
off with a clutch. The speed controls the amount of
cooling.

48. A/C Systems
• There are two types of way to control the electric scroll
compressor.
1. Send high-voltage three-phase A/C from a separate
inverter within the main inverter.
2. Send high-voltage D/C straight to the compressors
onboard “Mini” inverter, and invert it internally.

49. A/C Systems

50. A/C Systems

51. A/C Systems
• Some vehicles like Honda use a belt driven/Electric compressor.
It has two scroll compressors internally that can either be driven
together or separate.

52. A/C Systems
• Also be aware that using MAX A/C on any hybrid will
decrease mileage, by using more battery power. If the
vehicle has an “EV” mode or “Econ” mode, MAX A/C may
be unavailable.

53. Special Oil
• A/C compressors require
lubricant. Most use
polyalkylene glycol (PAG)
but this oil is electrically
conductive.
• In hybrid vehicles a special
non-conductive oil Must be
used. It is known as Polyol
Ester (POE).

54. A/C Service
• Because of the special oil, a separate “RRR” machine and
or manifolds must be used. Any cross contamination
results in high-voltage insulation loss, creating an
electrical hazard.

55. A/C Service
• There are some special tools you can buy to use your
existing machine. It service as an oil separator, keeping
PAG and POE separate. But this is not advised by most
manufacturers.

56. A/C Service
• Overall, the service and diagnosis of hybrid HVAC
systems is no different than conventional vehicles.
• If there is a high-voltage circuit fault, it will be combined
with a fault DTC.

57. A/C Service
• If your diagnosis requires
you to remove the
compressor or its wiring,
be sure to follow ALL
manufacture service
procedures…remember
there is HIGH-
VOLTAGE AC or DC
present……..

58. A/C Service
• If your diagnosis requires
you to remove the
compressor or its wiring,
be sure to follow ALL
manufacture service
procedures…remember
there is HIGH-
VOLTAGE AC or DC
present……..
DANGER!

59. A/C Service
• If your diagnosis requires
you to remove the
compressor or its wiring,
be sure to follow ALL
manufacture service
procedures…remember
there is HIGH-
VOLTAGE AC or DC
present……..
DANGER!

60. A/C Service
• If your diagnosis requires
you to remove the
compressor or its wiring,
be sure to follow ALL
manufacture service
procedures…remember
there is HIGH-
VOLTAGE AC or DC
present……..
DANGER!

61. Remote A/C Operation
• Gen III Prius and newer have an optional remote
controlled A/C operation, to cool the cabin before you
enter.

62. Remote A/C Operation
• This creates a risk to the technician, if somebody pushes
the remote button. The A/C system (high-voltage) will
turn on). Follow all service procedures as outlined.

63. Solar Ventilation
• Some hybrids and electric vehicles have solar panels on
the roof that operate cabin ventilation motors. These
systems have voltage, as long as the operating conditions
are met.

64. Solar Ventilation
• To perform repairs on this system, turn off switch, and
cover the solar panels.

65. Battery Heating and Cooling
• The vehicles HVAC can also be used to control high-
voltage battery temperature. (Ford)
• Which means the A/C compressor or auxiliary heaters can
come on even when the A/C is off!

66. Battery Heating and Cooling
• Since these systems use the vehicles HVAC to regulate
battery temperature, they are no longer consider optional
repairs or maintenance.

67. Battery Heating and Cooling
• The Freon runs through a liquid to liquid heat exchanger
called a “Chiller”. This Freon loop has its on TXV.

68. Battery Heating and Cooling
• Some hybrids also have three “12Volt” heaters, similar to
glow plugs in-line to the battery.

69. Battery Heating and Cooling

70. Battery Heating and Cooling
• The system is monitored by the hybrid/battery module,
using temperature sensors to regulate correct temp.

71. Battery Heating and Cooling
• Here is how it all works together, with the valves.

72. Filtering
• The air entering the passenger compartment and battery
must be filtered for debris. Always check this first if you
have an overheat code.

73. Filtering
• Prius air-cooled battery filter inlet

74. Filtering
• A plugged passenger compartment filter can reduce air
flow.

75. FINISHED!