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1999 Dodge Ram Van 1500 Starcraft Conversion AC/Overheating question


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Vehicle in question Info: 1999 Dodge Ram Van b1500, 5.9 magnum engine, automatic, 120,000 miles, purchased from a private owner.


My post might be a bit lengthy, but bear with me.  I would like to inform you everything I know and or have done to this van.  My actual question is further down.  It is by no means a jewel, and really shouldn't have bought it, but we are stuck with it now and really need to figure out the issues we are having with it.  We need it for long distance travel for my dad's doctor visits.


Brief synopsis from previous owner as was posted in the listing.  The van has all new brakes, calipers, rotors, two new brake lines in the front, wheel bearings, abs wheel speed sensor, front blower motor/fan and resistor, and a/c was charged and blows cold.  The owner proceeded to call us and informed us of mild overheating and the a/c only blows out the defrost in the front.  When turning a valve under the hood going to the heater core, the overheating stopped but only hot air blows out the rear.


Quick info about what I've done to it to fix problems I've come across.  I tore apart the dash and was unsuccessful in getting it out, so I ended up finding what (I am assuming is called but I may be dead wrong; I'm no mechanic) the actuator that controls the vent doors.  All vacuum lines seemed fine under the hood and behind the dash so I went here. Found the arm that moved the vent door.  Found it was broken off but was able to reach in and move the doors to vents and no longer blowing from the defroster. I'm aware the arm needs replaced and possibly the actuator (still not sure if that's what its called.  It has two vacuum lines that run into it and the arms connect to it and push them in and out) but we are fine with not fixing it since I cannot seem to get the dash apart to get down to it and would cost an arm and a leg to have a mechanic do it for us.  I can manually moved it to defrost in the winter if need be, but will leave it in the vent position during the hot summer.

After everything I have done to this van at this point, I was growing more satisfied that we would have front working a/c and rear working ac. (I thought the overheating was fixed after I changed oil.  The previous owner must have never checked it as it was near out of oil when we got it.  Added a quart and still read nothing on the dipstick.  After the oil change and a little STP oil treatment, it seemed to run cooler. But it turns out the overheating persists.)



So apparently, when this "valve" on the hose under the hood is turned, which I am assuming is the "open" position, the van runs just fine.  Never runs over 210 on the temp guage.  BUT, the air coming out the rear vents are all HOT.  If I "close" the valve (perpendicular to the hose) the rear a/c blows cooler air.  BUT, the engine overheats.  The heat doesn't seem to rise fast, it rises to normal temp (about 210) at the same speed as if it was closed, but it continues to rise.  It rises even faster if I have to slow down and accelerate back up to speed.  It finally got close to the red line and I pulled it over and turned off the A/C and put the valve back to the "open" position and proceeded down the road with it.  The overflow tank was gurgling, so I assume it was close to boiling over.  But with that valve turned back and the A/C off, the airflow of moving down the road brought the temperature back down quite rapidly.  (Also could note that an earlier drive I just turned off the A/C and the temps slowly started to decline, without turning the valve back to the "open" position.  But the the most recent test drive when the temp neared the red line and started to boil over, I had to pull over and put the valve back to the "open" position.  Even after turning off the A/C the temp continued to rise.)


Any ideas on what might be causing this?  I have a few theories, but am at the end of the rope.  We should not have bought this van, but we need to make it work.  It drives straight as a string and really would be nice for long trips.  But we can't afford to take it to be fixed nor can really get rid of it.  I am going to have to come up with a fix or drive it as is without a/c, which kind of beats the purpose of driving in a comfortable conversion van on long trips for the passengers if its hotter than heck in the back.


Is there another "blend door" for the rear that might not be closing? I can see the blend door under the glovebox and it is working.  I doubt it since the a/c does blow cold back there but only when that valve is closed.  If anyone could clarify what that valve is and if it is suppose to be open or closed let me know.  I'm assuming closing in the summer time is what its designed for so there isnt heat getting to the back.  Just A/C.  And something else is causing the van to overheat.


Could it be a faulty thermostat?

I can't tell, but I wonder if the radiator fan is working right?  Any easy way to tell if its actually spinning or not without losing a finger?

Radiator is a little dirty, but I took the grill out and hosed it down.  I could drive it up on ramps and blow out the back side of the radiator and try that and see if it helps.


Thanks a million to whoever ( I am assuming this goes up onto a forum) helps me figure this out.   


2 Answers

If there's a manually-operated valve under the hood for the heater core that indicates the HVAC may have been butchered in other ways by a previous owner to work around problems. If it was factory it would be vacuum operated or solenoid operated.

For the overheating problem the 23-year-old radiator is certainly suspect, as is the thermostat which may not be fully opening.

You should be able to tell if the radiator fan is working by observation if visible, or listening for it (it would be quite noisy), as the engine heats up. Cold spots on the radiator would indicate a clog.

AC problem could be low refrigerant. You'd need to hook up a manifold gauge set to check pressures to start diagnosing it. It's also possible the rear AC has a bad expansion valve.

I would focus first on solving the overheating problem since you really can't drive it that way. Once that's under control you can attack the HVAC issues.

so the rear expansion valve. where would that be located?

Most likely near the rear evaporator. I don't know the details of that vehicle and being a conversion van it may well be different than a stock Dodge setup. More diagnosis is needed. Throwing parts at a problem rarely ends in a good result.

Yeah I agree. Really wish we had an undo option in life. I talked my dad into looking for a van, but I also tried to talk him out of this one. Oh well. We've got it now. The overheating isn't an issue with that valve in the right position. But we may have to figure somthing out for the passengers comfort.


Try to rotate the fan by hand and if there is little or no resistance felt, the fan clutch needs replacement.  Any original cooling system parts on this 22 year old vehicle are suspect, including the temperature sending unit on the intake manifold.