6.7L Cummins Forum

A manually controlled single zone type heating-air conditioning system or a manually controlled dual zone type heating-air conditioning system is available on this model.
To maintain the performance level of the heating, ventilation and air conditioning (HVAC) system, the engine cooling system must be properly maintained. The use of a bug screen is not recommended. Any obstructions in front of the radiator or A/C condenser will reduce the performance of the A/C and engine cooling systems.
The engine cooling system includes the radiator, thermostat, radiator hoses and the engine coolant pump. Refer to 7 - Cooling for more information before opening or attempting any service to the engine cooling system.


All vehicles are equipped with a common heater, ventilation and air conditioning (HVAC) housing (1). The system combines air conditioning, heating, and ventilating capabilities in a single unit housing mounted within the passenger compartment under the instrument panel. The HVAC housing includes:

• Blend-air door(s) and actuator(s) (2)
• Recirculation-air door and actuator (3)
• A/C evaporator (4)
• Blower motor (5)
• Blower motor resistor (6)
• Evaporator temperature sensor (7)
• Heater core (8)
• Mode-air doors and actuators (9)

Based upon the system and mode selected, conditioned air can exit the HVAC housing through one or a combination of the three main housing outlets: defrost, panel or floor. The defrost and the panel outlets are located on the top of the housing and, the floor outlet is located on the bottom of the housing. Once the conditioned air exits the HVAC housing, it is further directed through molded plastic ducts to the various outlets within the vehicle interior. These outlets and their locations are as follows:

• Defroster Outlet - Four defroster outlets are located in the instrument panel top cover, near the base of the windshield.
• Side Window Demister Outlets - There are two side window demister outlets, one is located at each outboard end of the instrument panel top cover, near the belt line at the A-pillars.
• Panel Outlets - There are four panel outlets in the instrument panel, one located near each outboard end of the instrument panel facing the rear of the vehicle and two located near the top of the instrument panel center bezel.
• Front Floor Outlets - There are two front floor outlets, one located above each side of the floor panel center tunnel near the dash panel.
• Rear Outlets - On Mega Cab models there are two outlets located at the rear of the center front seat.

Both the manual temperature control (MTC) single zone heating-A/C system and the dual zone heating-A/C system are blend-air type systems. In a blend-air heating-A/C system, a blend-air door controls the amount of conditioned air that is allowed to flow through, or around the heater core. In the available dual zone system, two blend-air doors are used to provide completely independent side-to-side temperature control of the discharge air. The temperature control(s) determines the discharge air temperature(s) by operating the blend door actuator(s), which move the blend-air door(s). This design allows almost immediate control of output air temperature(s).



NOTE: Typical blend-air type HVAC system shown.


The heating-A/C system pulls outside (ambient) air through the fresh air intake (4) located at the cowl panel at the base of the windshield and into the air inlet housing above the heating, ventilation and air conditioning (HVAC) housing and passes through the A/C evaporator (7). Air flow is then directed either through or around the heater core (2). This is done by adjusting the position of the blend-air door(s) (3) with the temperature control(s) located on the A/C-heater control in the instrument panel. Air flow is then directed out the floor outlet (8), instrument panel outlet (10) or the defroster outlet (1) in various combinations by adjusting the position of the mode-air doors (9 and 11) using the mode control located on the A/C-heater control. The temperature and mode control uses electrical actuators to operate the air doors.
The velocity of the air flow out of the outlets can be adjusted with the blower speed control located on the A/C-heater control.
The fresh air intake can be shut off by pressing the Recirculation button on the A/C-heater control. This will operate the electrically actuated recirculation-air door (5), which closes off the fresh air intake. With the fresh air intake closed, the conditioned air within the vehicle is pulled back into the HVAC housing through the recirculation air intake (6) located within the passenger compartment.
On models equipped with A/C, the A/C compressor can be engaged by pressing the A/C (snowflake) button on the A/C-heater control. It will automatically engage when the mode control is set in any Mix to Defrost position. This will remove heat and humidity from the air before it is directed through or around the heater core. The mode control on the A/C-heater control is used to direct the conditioned air to the selected system outlets.

The defroster outlet receives airflow from the HVAC housing through the molded plastic defroster duct, which connects to the HVAC housing defroster outlet. The airflow from the defroster outlets is directed by fixed vanes in the defroster outlet grilles and cannot be adjusted. The defroster outlet grilles are integral to the instrument panel top cover.
The side window demister outlets receive airflow from the HVAC housing through the molded plastic defroster duct and two molded plastic demister ducts. The airflow from the side window demister outlets is directed by fixed vanes in the demister outlet grilles and cannot be adjusted. The side window demister outlet grilles are integral to the instrument panel. The demisters direct air from the HVAC housing through the outlets located on the top corners of the instrument panel. The demisters operate when the mode control knob is positioned in the floor-defrost and defrost-only settings. Some air may be noticeable from the demister outlets when the mode control is in the bi-level to floor positions.
The panel outlets receive airflow from the HVAC housing through a molded plastic main panel duct, center panel duct and two end panel ducts. The two end panel ducts direct airflow to the left and right instrument panel outlets, while the center panel duct directs airflow to the two center panel outlets. Each of these outlets can be individually adjusted to direct the flow of air.
The floor outlets receive airflow from the HVAC housing through the floor distribution duct. The front floor outlets are integral to the molded plastic floor distribution duct, which is secured to the bottom of the housing. The floor outlets cannot be adjusted.

NOTE: It is important to keep the air intake opening clear of debris. Leaf particles and other debris that is small enough to pass through the cowl opening screen can accumulate within the HVAC housing. The closed, warm, damp and dark environment created within the housing is ideal for the growth of certain molds, mildews and other fungi. Any accumulation of decaying plant matter provides an additional food source for fungal spores, which enter the housing with the fresh intake-air. Excess debris, as well as objectionable odors created by decaying plant matter and growing fungi can be discharged into the passenger compartment during heater-A/C operation if the air intake opening is not kept clear of debris.


The A/C system on models so equipped is designed for the use of non-CFC, R-134a refrigerant and uses an A/C fixed orifice tube located in the liquid line to meter the flow of refrigerant to the A/C evaporator. The A/C evaporator cools and dehumidifies the incoming air prior to blending it with the heated air. To maintain minimum evaporator temperature and prevent evaporator freezing, an evaporator temperature sensor is used to supply evaporator temperature input to the A/C-heater control. The powertrain control module (PCM) cycles the A/C compressor clutch off and on as necessary to protect the A/C system from evaporator freezing and optimize A/C system performance.

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2007.5 Dodge Ram 3500 HD,QC, 6.7L Cummins, 6speed Auto, 4X4, Bighorn Edition.
Click for installs: Carr Steps PML Diff Cover Edge Juice with Attitude Volant Intake Hankook ATM RF10

Dang Squid, where did you get all this tech info? Its awsome, lots of good reads here

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07 2500 4X4 MegaCab 6.7 Edge Juice W/Attitude EGR unplugged Intake Baffle MIA XRT TUNNER 5" TBE 6" AUSSIE STACKS (INSTALLING NOW)

squid, when should voltage be present at the compressor?

mines shows +12v one on lead, and ground on the other, all the time.

??

i can turn the compressor by hand.