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?
Re: 1995 Dodge diesel. Heater fan runs but no air flow....
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.
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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.
Lack of sufficient vacuum can cause the heater to not work.
The low vacuum could be due to a vacuum leak somewhere before it gets to the controls or the heater box.
Then, the heater box or flaps could be stuck or warped, causing malfunction.
It is all repairable, but can cost you a lot of time and effort fixing this.
God bless your efforts.
If there is no vacuum to the mode door control motor theheater/A/C system will default to "Defrost" If there is no air coming out the vents or floor - check to see if you have air blowing out the defrost vents. If there is air coming out the defrost, then the most likely cause of your problem is a broken or disconnected vacuum line that feeds the mode control switch. On your vehicle, the vacuum supply line connects to the brake booster hose under the hood. there is a check-valve on the line between the firewall and the brake booster that can fail and leak vacuum. if there is no problem with the vacuum supply line under the hood, then the most likely cause is a bad mode control switch. (switch leaking vacuum)
If there is no air coming out the defrost vents, but you can hear the blower motor running, there is most likely a resriction of airflow etween the blower motor and the air outlet plenum. I have seen A/C evaporators completely cloggedup that will not pass any air. I have also seen paers and napkins that have gotten sucked out of the glovebox area and into the "Recirc" air inlet. Another thing I have seen several times is nests made by mice or other small rodents in the blower motor housing.
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.
You may have a vacuum leak affecting the vacuum supply to the control switch. I don't have the manual for your car, but if you have a vacuum operated valve on your heater hose, that could also limit the flow of hot water to the heater core. Look for the small vacuum line that goes from the engine intake manifold through the firewall to the control switch. Look closely at the connection to the intake manifold, as that is one of the primary failure modes. the other typical failure is the vacuum switch itself. If you can get to back of the control switch and pull the vacuum connector off the switch, check for vacuum on the supply line from the engine with the engine running. If you're getting a good vacuum there, your switch is likely the problem. Let me know if you have more questions.
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.
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.
The actuator that controls air flow in the rear is vacuum controlled. You need to remove the rear quarter trim and access the heater/ ac box. Look for a plastic vacuum hose and see if vacuum is present when you switch between a/c and heat. If vacuum is not present then you need to trace the vacuum hose back to the engine compartment where you will likely find it is cracked or melted. If vacuum is present then test the actuator to see if it holds vacuum(you will need a handheld vacuum pump). If it doesn't then replace it.
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 heatertreater.net 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.