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Most systems use a "digital" control for vent selection and re-circ. By digital, I mean 1/0, open/closed, and this type of control is easily done with vacuum control. The vacuum switch is either on or off, and the door open or closed. This is fine for all the control functions other than the blend door. No one want the fine control of being able to put 90% of the air through the defrost and 10 through the floor and then decide to change it to 73% through the defrost and 27% through the floor, so it's either on or off with no fine control. The blend door is different because you want the control to be able to change the temperature from 73 degrees to 72 degrees and this is accomplished by moving the door slightly to change the mix of air going through the heater core.
Vacuum control is problematic because you have to connect to the engine intake system, run little tubes to the various functions, use mechanical vacuum switches...and hope it doesn't develop leaks over time. Dodge avoided the vacuum "problems" by using electronic servo motor control for all the HVAC functions. The scheme connects a small DC motor to each of the door axles with control from the central computer. Each motor has two wires(not three) and the computer controls the direction of movement by reversing the voltage polarity on these two lines. The problem is that the computer has to know the point when the door is fully closed or fully open. It finds this point by driving the door to the extent of movement and recording a voltage signal from a stalled motor. Think of it like rolling up a hand cranked window. How do you know when the window is fully up or down. Easy, you can watch the window and stop just in time or turn til you feel resistance to movement and stop. Most of us have better sense than to torque the handle hard after it stops moving, but the computer system in the RAM does not have the same sense. It torques the door HARD every time it checks for the extents of movement and will eventually break the axle connector or the cheap plastic doors used on the RAM. This is the root cause of all the failures on the different control doors. The RAM is worse than the other automobiles we look at because of the decision to use servo motor control for all functions where most trucks use the motors for blend doors only. Once you break a door, the approved Dodge repair process is to disassemble the dash, disconnect the coolant and refrigerant lines, and remove the plenum box. It's fairly simple to open the box and replace the plastic doors with new plastic doors that will also fail over time. The doors are cheap, but the labor to disassemble the truck to get to the door will run in the $1k range. There are aftermarket solutions that avoid the high dollar work.
So, let's follow the air through the system and look at the different doors that control the flow.
1. Air enters the system through either an external vent or internal vent(re-circ). This is an either/or choice. If both the external and internal vents are open, air just flows into the external intake and out of the internal intake at highway speeds...like having a window rolled down all the time. The re-circ door is easy to see if you are having these kinds of symptoms by fully opening the glove box and looking to the upper right. With re-circ off, the door should be pressed against the inside of the grate covering the internal intake port and it should move when you turn re-circ on. If it isn't moving, it is broken and needs to be replaced.
2. The air taken in in #1 now flows through the evaporator core. If the compressor is running, the air is cooled, if off the effect is neutral. The air is either cooled or ambient depending on the electronic signals to the clutch on the compressor. Air now hits the blend doors which can divert some or all of this air through the heater core. For max AC, you want the compressor on and no air through the heater core and for max heat you want the compressor off and all air diverted through the heater core. The system can change the on/off cycle of the compressor and position of the blend door to regulate temperature between max heat and max AC. This is the only component in the system that regulates the temperature of the air flow. If you are seeing problems with temperature control, the leading suspect is a broken blend door. Dodge also threw another curve into this by designing separate ducts for passenger and driver with some added complexity and two motors for the dual control systems. The plenum box is the same with either dual or single control and a differential between passenger and driver temperatures is a strong indication of blend door breakage.
3. The conditioned air from the blend door now flows through the Mode 1 door. This door selects between dash vent and defrost/floor. If you have air flow through the dash vents all the time or no flow through the vents all the time, the Mode 1 door is broken. The door can physically break off and lodge in strange positions so it may not be completely black and white, but inability to control the dash vents is a broken Mode 1 door.
4. The Mode 1 door will either push air out of the vents or allow the air flow to go to the Mode 2 door. This door chooses between the defrost vent and the floor vents. The system is designed to be a little "leaky", so choosing defrost will put most of the flow onto the windshield with a little leakage to the floor and the opposite situation when the door chooses to allow air to the floor. An inability to regulate between defrost and floor is an indication of a broken Mode 2 door.
All four systems are equally susceptible to failure. Since the computer system is capable of detecting the movement extents of all four systems, it is also capable of throwing codes for a failure of any of the doors. The above describes the symptomatic analysis of the system, but the codes will also show any problems. The best diagnosis is to see a symptom that matches a code. You have to have the special Chrysler computer diagnostic system to read the codes. You may be able to find a shop that will do this for little cost, or maybe borrow a reader from one of the big parts chains. Note that the doors will "bend" before they break and the variation in calibration can throw codes even though the doors are not yet broken. The door may operate OK even with a code, but once you see a code, it's only a matter of time until it breaks.
I know, I know, waaaaay too much information and complexity. Blame Dodge, not me. Unfortunately, theres more if you go looking for it. The system can be reliably repaired without extensive work and cost.
Your symptoms are indicative of a Mode door failure and the system can be repaired for less than the dealer wants for a new motor that won't solve the problem anyway. You can search the internet for more information on diagnosing and solving the problem.
The RAM has four different electronically controlled doors in the system and most likely your problem will be traced to one or more of these systems failing. The four actuator motors are connected directly to the plastic control doors and it is a common failure for the plastic to break and lose control over the door. Once this happens, the computer system detects a fault in the system and you can get all kinds of strange behavior. Once a failure is detected, the computer shuts down the suspect actuator motor and goes into a state of confusion. The motors themselves are actually fairly robust, but the plastic doors are weak and break.
Here are the four systems you need to check:
1. Re-circ door - regulates between internal and external air into the plenum box.
2. Blend door - diverts some or all of the air flow through the heater core to regulate temperature.
3. Mode 1 door - controls air flow to dash vents or defrost/floor.
4. Mode 2 door - when mode 1 diverts the air away from the dash vents, this regulates between 90% defrost and 90% floor.
The diagnosis is fairly simple. You can read the codes with a special Chrysler computer diagnostic tool. You may be able to get one of the big parts stores to do this for free if they believe that they can sell you something, or go by the dealer and pay for a diagnostic report. The other way is to analyze the symptoms and examine the plenum box. You can easily figure out the problems once the center console and glove box have been pulled. Figure a couple of hours work.
There are aftermarket solutions for the weak doors and full diagnostic procedures to trace and resolve the problems. The work is well within the skills of most shade tree mechanics and significantly cheaper than the dealer fix.
At first I had a fan problem and had to bang on it to jump start it... finally bought a new fan and replaced it. Still works good.
Then the A/C would work on driver's side and heat on passenger side. Driving across country in the middle of the summer it was a pain. Finally stopped in Lawrence, KS(?) and the tech told me that he it was the valve system and he worked them until they worked ok. They did and no charge.
It's Apr 09 and it started doing it again. I would tear into it and do it myself, but I don't have a clue as to where these "valves" are or how to get into them.
I live in San Diego and the closest dealer to me is in Escondido and really hate to take it there as they ALWAYS try to do the most expensive thing that there is... Which would be the truck computer... no way jose.
Would appreciate it if some one could give me an idea where these valves are and any little secrets of how to get to them.
Never had this in my Ford
Anyone can help? Thanks
Ski in TX
kcram - Pickups/Wagons Host
The internal intake port is located behind the glove box in the upper right corner. With the fan running and the system on re-circ, any liquid sprayed into the intake will be pulled through the evaporator core. Don't worry about too much liquid as it will be blocked by the core and drain out the bottom through the hose mentioned above.
HeaterTreater
HeaterTreater
On the single control both the top and bottom set of doors have the same problem with a weak connection between the doors and if you have a broken one on either pair, you'll get strange HVAC behavior. There are aftermarket solutions for this problem, and additional pictures and video that can be found on the internet.
HeaterTreater
Harry
I think you are seeing the door move to a closed point, then slipping and falling back. It will only get worse. In order to diagnose the problem, you will have to get to the plenum box and remove the actuator motor and examine the axle connector. There is a video on YouTube that will give you a step by step process to get to the box, along with information on how to diagnose problems, and a repair procedure that might be of interest. Search "Dodge Ram Heater" to find the video.
HeaterTreater
kcram - Pickups/Wagons Host
Charging the system may solve the problem and at least it should be checked, but this can be problematic if your truck is red-flagged as a "leaker". The R134a refrigerant is much less destructive than the old Freon systems, but the EPA regulations are the same. There are stringent requirements for recapture/recycle/repair of leaking refrigerant. You can get caught in government regulations that any suspected leak be repaired to stringent requirements which of course can get into big bucks in a hurry. You can buy recharge cans of R134a at any auto parts store, but it's a shot in the dark to just add refrigerant without monitoring the high and low side pressure and ambient temperature. It's worth it long term to own an AC gauge manifold and learning how to correctly evaluate and charge the system. Harbor Freight has a set that won't break the bank and you may become the most popular resident in the neighborhood with just a little learning. You may also be able to get one from the larger parts stores under their tool loan programs, but the instructions will probably be missing and you'll need to do some online learning. Of course, you need to evaluate your own conscience on doing this, and decide whether or not you will be single-handedly responsible for destroying the planet.
If the core is OK, the next suspect is the blend doors. Dodge has a strange clam shell door arrangement for the doors in the RAM. There are two doors, an upper and lower that move in unison and cover the top and bottom of the heater core which is on a horizontal plane. On a single control system there are four different flaps(two sides/two sets of doors) that have to operate correctly. The plastic components are susceptible to breakage and it is an expensive repair to remove and repair the plenum box when this inevitably happens. Check the HeaterTreater.net web site for diagnostic information and a video of the analysis and repair process with an aftermarket solution. The RAM system is overly complex and has multiple design weaknesses that will show up over time. Complete information and pictures are available on the web site mentioned above.
Sorry for making this so complex, but it is! However, maintaining and repairing the system is within the capability of most DIY'ers and much much cheaper with just a little learning and effort.
HeaterTreater
HeaterTreater has a DIY kit to replace the door by just removing the glove box panel, and provides a metal replacement door that will withstand the forces in the system for the life of the RAM. Check their web site(heatertreater.net) for diagnostic information and a video showing the replacement process.
This is a common problem with the RAM and is not confined to just the re-circ door. The RAM has four door systems for blend and airflow control and all of them are susceptible to the same fail mode as the re-circ door. While you have the dash open to replace the re-circ door, you should also check the other doors to see if there are additional problems. The two most common fails are the re-circ door and the mode 1 door(controls air distribution for vent VS floor/defrost. Full information is available at the above site.
The actuator motor is calibrated by the computer and does not require any special alignment when installing the motor. There is a limit pin on the door axle that constrains the movement of the door between two stop points molded into the housing. The blend doors/Mode 1 door/Mode2 door all have two stop points for open/closed. However, for some unknown reason, the re-circ door only has one stop point and all force is transferred directly to the door in re-circ mode. This makes the plastic door more susceptible to failure and the design flaw is what's responsible for the failure you are seeing. While the re-circ door is a little worse with only one stop, the other doors aren't much better and over time this will be an ongoing failure issue. The doors aren't particularly hard to fix with the HeaterTreater kit, but you need to know what to look for and keep an eye on the system.
This is going to sound like shameless self promotion, but since you already have a little frustration with the dealer, why not mess with their minds a little. Suggest that you want warranty work done on your truck, but want HeaterTreater metal doors installed to replace all the cheap plastic and demand that they pay for the parts to make up for obvious design flaws in the system. You would end up with a long term reliable system and no cuts in the box.
There's no way in he11 they'll go for it, but at least you can get a little satisfaction from being smarter about the Dodge Ram than they are..... In reality this would be a smart customer focused move on their part, but I wouldn't count on it.
1. All air flows through the evaporator core into the two channels. On other dual control systems, the evaporator coils run vertically and if there is a gradient across the core, it is equally divided between the passenger and driver's side channels. On the RAM, the core runs horizontally from the driver's side chamber to the passenger side chamber. If there is a differential across the core, the drivers side will be cold and the passenger side which is further downstream will be warmer. If the refrigerant charge is low, the impact of having the evaporator core designed 90 degrees out of phase is that the drivers side will be cooler. This problem is solved by having the coolant charge perfectly adjusted...not too low, not too high. This is actually a design flaw in the system and there is no good solution other than keeping the charge perfect.
2. The system has two sets of blend doors that operate in unison and "clamshell" around the heater core. Each set has two doors(two flags on the flagpole). The connection between the two "flags" is a weak point and the back door can snap off, leaving one side of the heater core exposed on one side. The driver's side which is the front one can be completely normal, but the back door can be broken. This will also cause a temperature differential like you are seeing. The only way to determine if this is the problem is "exploratory surgery" to get into the box and check for a broken door.
My best advice would be to check the refrigerant charge and make sure that it is correct. If this doesn't solve the problem, I'd suggest getting the HeaterTreater blend door kit and following the instructions to get into the box and look for problems. You would also be able to physically check the temperature across the core when the box is open. You will be able to at least get enough information to figure out the problem.