HVAC Airflow
Heating, ventilation, and air conditioning bring lots of comfort into our vans. They can be divided into a few different main sections.
Blower/ventilation - Consists of a blower motor, fan, duct-work, diverters. All heating and air conditioning depends on the blower section(s) working properly.
Heating - Coolant flows through the heater core, the blower moves air across the core and into the cab.
Air conditioning - Uses an engine driven compressor to move heat away from the evaporator coil, the blower moves air across this coil, removing the heat and moisture from the air entering the cab.
In this section we are going to talk about the blower/ventilation side of things.
The single most common problem with the blower/ventilation airflow in our vans is when the airflow gets diverted to the defroster vent when under load(like going up a hill), or sometimes the leak is so bad that it will constantly be on defrost. Some get stuck on the floor vents.
The first thing to do is check/replace all of the vacuum hoses under the hood. The hoses under the hood have to deal with a lot of heat, so they tend to break down a lot faster than the ones in the cab. They are mostly 4mm and 6mm hoses and can be replaced for just a few dollars in hose from your LAPS. The easiest way is to replace 1 hose at a time, that way you don't need a diagram and makes it impossible to mess up. The most common hose that needs replacement is the one that goes from the tee down to the vacuum storage ball, which can be accessed from the front passenger side wheel well. Second most common hose is the one from the vacuum source that runs across the top of the engine to the tee.
Note: The check valves are cheaply made and even good ones have been known to be bad right out of the box, please ensure proper function of the check valve.
In the above picture, the orange tee, purple hose and blue heater valve are for the rear heat. If you have rear heat the yellow valve in the picture will be a 6port valve, if you don't have rear heat it will be a 4 port valve.
You don't have to buy factory vacuum lines, I used 50211 armor mark 7/32 or 5.5mm hose to replace the blue line from the PCV valve cover to the tee/check valve. https://amzn.to/3oDut9M
The engine supply comes from the PCV valve cover, in the image above it does not show the PCV valve nor the cover on the upper intake manifold. But it is this part below.
PCV valve, hose and cover
Blower motor not functioning on 1 or more speeds:
Not blowing on any speed - Check fuses, connector, wiring, check voltage to blower motor.
Can hear the blower working, but no airflow - Check for a physical blockage at the blower motor, stuck re-circulation door.
Working on all speeds except high - Check fuses, connector, wiring, and blower motor relay.
Working on high but no lower speeds - Check fuses, connector and resistor pack/controller.
Blower motor resistor blown and/or burnt connector.
When the blower motor gets worn or has a physical blockage it uses more current to operate. If it's just a blockage, you can replace just the resistor/controller, and if needed the connector. However, if there is no blockage, and the motor is overloading the resistor/relay/connector you should replace the blower at the same time you replace the resistor/relay/connector.
Example of a burnt blower motor controller connector:
New connector soldered in after cutting off old connector, heat shrink tubing applied:
Never operate the blower when either the resistor/controller or blower motor are not installed. The resistor pack on the controller requires airflow to cool it and can burn out quickly.
Note: The front blower on 96 and newer use a combination resistor pack and high speed relay, as seen in the picture below.
96 and up blower motor controller/resistor - http://amzn.to/2nGafOB
96 and up blower motor http://amzn.to/2gYCdlV
Thermal fuse: https://amzn.to/2Oc5VTj 167°C 10A 250V often available on ebay as well https://www.ebay.com/sch/i.html?_from=R40&_nkw=167°C+10A+250V+thermal+fuse
Inspect connector https://amzn.to/2O1P7it
When installing the new style blower motor controller, you can either cut the housing to fit or you can gently bend the pins to bring them closer, then you don't have to trim the housing.
Here is an example wiring diagram for an 02:
Example Wiring Diagram for a 96:
Up through 95, they have a separate relay, the resister pack looks similar to:
Replacing the blower motor controller/resistor:
Pretty self explanatory, make sure to inspect the wiring side as well. Make sure it's installed before testing as it requires airflow from the blower to keep cool and can burn up quickly otherwise.
How much amperage should my blower motor be drawing on high?
This depends on a few factors such as model/age/etc, but as a general reference it should be less than 18amps.
Replacing the blower motor:
Remove the windshield washer and coolant recovery tanks.
Disconnect the wiring and remove the bolts. On later years you have to cut the case along the groove with a utility knife, it cuts very easily.
Remove the blower motor.
Reverse to reinstall.
HVAC Mode Switch - 2nd and 3rd GEN
The mode switch is a rotary vacuum valve that directly applies vacuum to the appropriate vacuum actuator. Use the mode switch to change the air delivery mode in the vehicle. Not sure if colors vary by year, consult FSM.
MAX A/C
When the operator selects MAX A/C, the mode actuator has vacuum applied to it through the Yellow vacuum line, making the vent door open. The defrost actuator has vacuum applied to it through the Green vacuum line, making the defrost door close and the heater door open through mechanical linkage. A solenoid inside the HVAC control assembly connects the recirculation door vacuum actuator to the vacuum source. The recirculation actuator retracts, allowing air to be recirculated. A/C is forced ON.
A/C
When the operator selects A/C, the mode actuator has vacuum applied to it through the Yellow vacuum line, making the vent door open. The defrost actuator has vacuum applied to it through the Green vacuum line, making the defrost door close and the heater door open through mechanical linkage. A/C is forced ON.
Bi-Level Mode
When the operator selects Bi-Level, the following occurs:
The mode actuator is in neutral position.
The defrost actuator has vacuum applied to it through the Green vacuum line.
The defrost actuator closes the defrost door, thus opening the heater door though a mechanical linkage.
Vacuum is bled off the mode actuator and the vent door is held stationary in the half open position.
A/C is forced ON.
Vent Mode
When the operator selects VENT, the mode actuator has vacuum applied to it through the Yellow vacuum line, making the vent door open. The defrost actuator has vacuum applied to it through the Green vacuum line, making the defrost door close and the heater door open through mechanical linkage.
Floor Mode
When the operator selects FLOOR, the mode actuator has vacuum applied to it through the Red vacuum line, pushing the vent door closed. The defrost actuator has vacuum applied to it through the Green vacuum line, pulling the defrost door closed and opening the heater door through mechanical linkage.
Mix-Blend Mode
When the operator selects Mix-Blend, the following occurs:
The mode actuator has vacuum applied to it through the Red vacuum line, pushing the vent door closed.
Vacuum is bled off the defrost actuator, holding the defrost door stationary in the half-open position. The heater door is also held stationary in the half-open position through mechanical linkage.
A/C is forced ON.
Defrost Mode
When the operator selects Defrost, the following occurs:
The mode actuator has vacuum applied to it through the Red vacuum line, pushing the vent door closed.
The defrost actuator has vacuum applied to it through the Blue vacuum line, pushing the defrost door open and closing the heater door through mechanical linkage.
A/C is forced ON.
Recirculation Operation
Recirculation is only available in MAX A/C. When MAX A/C is selected a solenoid inside the HVAC control assembly connects the recirculation door vacuum actuator to the vacuum source. The recirculation actuator retracts, closing the recirculation door.
HVAC Air Control Actuators:
My 03 has 4 HVAC air control actuators. Need to add a diagram or 3 here. Don't know if colors vary by year, consult FSM.
Mode Actuator - 3 Vacuum Controlled Red/Yellow lines - Under the center/pass side dash where the three air ducts point towards the drivers side - Selects where the air flows by controlling the mode/vent door, operates during all mode changes
Defroster Actuator - 2 Vacuum Controlled Green/Blue lines - Controls the defrost door - Neutral is half open/closed, Blue Opens, Green Closes
Recirculation Actuator - 1 Vacuum Controlled line- Passenger side kick panel - Only activates on MAX A/C
Temperature Actuator - Electronically controlled - Remove engine cover and look towards the passenger side, it's right there, electrical connector/no vacuum lines - changes the blend door to change the air temperature mix
85-95 HVAC Control
C102, C104, C109 connectors:
Though uncommon, sometimes these connectors can corrode or melt and need to be repaired/replaced/bypassed. This is showing a 2003 AWD. For the blower circuit, C102, C104, C109 are the important ones(see 03 wiring diagram for the function of each).
C104 is going to be the most common one, as that circuit is the one that supplies all of the current for blower motor when high speed is selected.
