AC Evaporator Core issues

The RAM plenum box is built with dual flow chambers so that the system can be configured for either single or dual control.  On the single control, the blend doors are just connected together and operate as a single unit, but there are still two separate air flow chambers.  The single control has a single motor to control both sides of the HVAC system while the dual control has separate actuator motors for either side.  Air flows through the AC evaporator core before getting to the dual chambers and if there is a temperature differential across the core, it can show up as a difference in temperature on the two sides.  Most auto makers constructed the core with refrigerant flowing from top to bottom on dual systems.  With this setup both sides would be the same and a lack of efficiency in the core would be equally spread across both sides.  Chrysler moves the refrigerant from right to left, so if there is a  temperature gradient across the core, the passenger side is at the back of the core and will see less efficient AC.  

Charging the system is usually the problem.  The factory spec on the RAM is low due to to the EPA setting minimum specs based on junk science with Freon and ozone depletion from the 90’s.  If you use a computer controlled refrigerant charging system, it is common to see this problem.  

What you have to do is tweak the refrigerant charge by measuring the temperatures on the driver and passenger side and make a chart.  You can use a can of R134a with a hose on it from Walmart to add a little refrigerant.  Measure/tweak/measure/tweak until the cooling on both sides start to equalize.  Note that you are violating federal law by overcharging the system.  You generally can't get enough pressue from a can to overcharge the system, but there is a blow-by valve on the system.  If you release the valve, it will scare the S out of you, but won't harm anything.  We do NOT recommend this procedure and you are on your own…  You can always blame Walmart or a parts store if the world comes to an end tomorrow and it is determined that you are the cause.  

If  the charge is too high or too low, it can cause a gradient across the core and it will show symptoms of warmer air on the one side.  This is a design flaw in the system and there is little margin for less than perfect operation of the AC compressor system.  The core is oriented such that any temperature gradiant is placed on one side or the other.  If the core were oriented 90 degrees different, the gradient would be shared like most vehicles.

You can “check” the operation of the blend doors by clamping off the two heater hoses going into the firewall on the engine side.  This takes all heat out of the system and you’ll be in max AC independent of the position of the blend doors.  If this restores good AC, the problem is the blend door.  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.  The only way to really diagnose this problem is to cut into the box and observe the operation of the doors.  Once you have the box open, you can also check the temperature of both sides of the AC evaporator core to make sure that it is cooling both sides efficiently.  It takes a little work to get to the doors and check the operation, but once you understand the root cause of the problem, it can be restored to fully efficient operation.  Our kit will restore the system to efficient heat/AC on both sides.

This is about a thousand dollars worth of free advice and in return, we’d appreciate if if you keep us in mind when your doors fail and speak well of us to fellow RAM owners or on any forums you might participate on.  


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