Question about 2002 Dodge Ram 3500 Truck

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1995 Dodge diesel. Heater fan runs but no air flow. Vacuum okay

Checked vacuum at mode switch = 20 inches. Pump supplies to 25 inches vacuum.Tried using a portable vacuum pump that goes to 26 inches vacuum but still no air flow. Recirc damper opens okay. Fan runs okay. No air flow comes from any port; floor, panel, defrost. I even tried vacuum at the mode vacuum hoses; still nothing. How can I get at defrost actuator without removing heater system from cab?

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Two actuators can be accessed (enough to move them) without removing it. One is on the bottom of the HVAC unit on top of the trands hump, you will probably have to remove the airbag module and cover to get to it. The other one is on the driver's side of the HVAC unit about half way up. Remove the driver's side knee bolster and you should be able to see it.

Posted on May 20, 2009


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One thought. Diesel engines do not produce vacuum. Since the heat and AC controls are vacuum actuated, and you have no heat, the main flap over the heater core is not being opened to allow the heat to come into the cab. Meaning it's getting no vacuum. Check that all vacuum lines are connected from the vacuum pump, then check that the vacuum pump is working. If the vacuum pump is not pulling vacuum, there's your problem. Makes sense, huh?

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Taking your heating box apart may be a really big job.
It would be good to check the vacuum supply at the heater box, and/or at the controls.
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1990 Dodge Caravan A/C / Heater blower fan mode control won't work

The mode doors are operated by vacuum. Check the vacuum supply line to verify it is connected to the intake manifold. If that looks good, remove the control panel to see if vacuum is coming to the mode switch. Then check to see if the switch is transferring vacuum to the actuator lines. Here is the panel removal procedure:
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  2. Remove the necessary bezel(s) in order to gain access to the control head.
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Jul 21, 2017 | Cars & Trucks

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2005 Silverado 2500HD 4WD - It appears that the pneumatic valve controlling the directional air flow from my heater/AC is getting stuck. When I switch the fan to front window defrost then back to...

The default configuration when all vacuum fails is to defrost vents. Most likely your vacuum supply to the switch is weak. Check the connection of the supply line to the intake manifold for damage. If no problem there, trace it to the switch on the control panel. If there is an accumulator, make sure it isn't leaking and is storing vacuum. If all this is good, look at any other vacuum lines connected to the intake manifold that may be leaking and possibly reducing the vacuum supply to the HVAC control line. Let me know if you have more questions.

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1 Answer

I have a 1999 Chevy Malibu and the AC turns from inside air output to outside output on it's own. You can push the inside air button and it will go back and then in a second or two it will go back to the...

Yes , the Refrigerant level is good , I would say the control panel is bad , or there is a problem with HVAC Air Delivery/Temperature Control Circuit Description
The vacuum actuators move the air valves in the HVAC system (except the temperature valve). Vacuum is applied to the actuators through the mode selector in the heater A/C control assembly. The mode selector consists of a rotary vacuum switch. The rotary vacuum switch supplies vacuum to the vacuum actuators according to the operating mode selected by the driver. A small servo motor moves the air temperature actuator. The small servo motor positions the door according to the voltage level from the temperature selector in the heater A/C control assembly. The temperature selector is a potentiometer positioned by the temperature control knob on the front of the heater A/C control assembly.
Air Temperature Actuator
When the ignition switch is in the RUN position, battery voltage is applied to the air temperature actuator. The actuator receives ground at all times through the following components:
• CKT 251
• Ground G204
The temperature selector is a potentiometer with a wiper arm. The wiper arm is electrically tied to the air temperature input through CKT 733.
When the temperature selector is moved between COLD and HOT, voltage to the control input varies between 1 and 12 volts. The temperature valve motor solid state circuitry performs the following tasks:
• Looks at the control input voltage
• Moves the motor to correspond to the control input voltage
The temperature valve moves for the following reasons:
• In order to allow the air to pass through the heater core
• In order to allow the air to pass around the heater core
This control achieves the desired passenger compartment temperature.

HVAC Air Delivery System Check
Start the engine.
Turn the blower motor fan ON and select an air outlet mode.
Does air flow out of the selected HVAC outlet ducts?
Go to Step 3
Go to Step 2
Did the customer concern mention that the air discharges out the correct ducts at first, but then changes during higher engine RPM?
Go to Step 7
Go to Step 3
With the engine running, cycle the HVAC controls through all the modes.
Does the air come out of the selected outlet ducts?
Go to Step 18
Go to Step 4
With the engine running, take a vacuum reading at the manifold vacuum port that supplies vacuum to the HVAC vacuum control assembly.
Is there engine vacuum?
Go to Step 6
Go to Step 5
Repair the no vacuum condition.
Is the repair complete?
Go to Step 18
Take a vacuum reading at the vacuum supply line at the HVAC vacuum control assembly.
Is the vacuum reading the same as the engine vacuum?
Go to Step 11
Go to Step 8
Disconnect the vacuum supply line from the HVAC vacuum control assembly.
With the vacuum gauge connected to the vacuum supply line, re-start the engine and turn the engine OFF.
Does the system lose vacuum after turning OFF the engine?
Go to Step 8
Go to Step 11
Inspect for leaking or collapsed vacuum lines between the engine manifold vacuum port and the HVAC vacuum control assembly.
Are the vacuum lines leaking?
Go to Step 9
Go to Step 10
Repair or replace the collapsed or leaking vacuum line.
Is the repair complete?
Go to Step 18
Replace the vacuum reservoir tank.
Is the repair complete?
Go to Step 18
Using an external vacuum source, apply vacuum to the appropriate vacuum line at the connector to the HVAC vacuum control assembly.
Does the actuator retract?
Go to Step 17
Go to Step 12
Inspect for leaking or collapsed vacuum lines between the actuator and the connector to the HVAC vacuum control assembly.
Are the vacuum lines leaking?
Go to Step 9
Go to Step 13
Disconnect the vacuum line from the actuator.
Apply an external vacuum source to the actuator.
Did the actuator retract?
Go to Step 14
Go to Step 16
With the actuator disconnected, inspect the door for binding.
Does the door move freely?
Go to Step 16
Go to Step 15
Repair the appropriate binding door.
Is the repair complete?
Go to Step 18
Replace the appropriate vacuum actuator.
Is the repair complete?
Go to Step 18
Replace the HVAC vacuum control assembly.
Is the repair complete?
Go to Step 18
Cycle the HVAC controls through all modes to verify proper operation.
Did you correct the condition?
System OK

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2 Answers

Where do the vacuum hoses go from the control 1999 Dodge Pickup

first ... Make sure that you have vacuum to your control head. This is normally the black vacuum line. The vacuum than goes to the various vacuum motors on the Heater /AC case. These vacuum motors rarely fail. The normal fault is loss of engine vacuum ..cut line or not secure to engine. second.. a fault with the vacuum reserve reseviour. When the engine needs the vacuum this is your vacuum supply.

Apr 25, 2010 | 1999 Dodge Ram

2 Answers

What vacuum level should I be getting from my 95 chevy diesel vacuum pump?

With the engine running it should read 20-21 in about 30 seconds if it is working properly. When you shut the engine off it should only lose 1 in. in about 11/2 seconds. You measure it at the pump inlet pipe. Hope this helps.

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3 Answers

The heater /air control for directing air to face and floor still only goes to windshield this is on a dodge 3500 diesel 4x4 2002 vin 7

Check for vacum leaks, under the dash at the control
panel. Also at the mode actuators on the heater box.
One is for heat/def, the other for panel/def. And the line at the nipple on the vacum pump. But if all the lines are tight, and the rods on the actuators are working properly. One of the mode doors may have
broken off. If this is the case the whole heater box has to be removed to replace it. If it comes to that
there is a website you can check out,
called They make a metel replacement door and an installation process that can be done in a fraction of the time it would take to
pull the heater box. I have not tried it myself, but I
know somone who has, and it worked out well for him. Hope this helps.

Mar 23, 2010 | 2002 Dodge Ram 3500 Truck

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