2nd Gen Ram Tech1994-2001 Rams: This section is for TECHNICAL discussions only, that involve the 1994 through 2001 Rams. For any non-tech discussions, please direct your attention to the "General discussion/NON-tech" sub sections.
I have a 2000 dodge ram 2500 gas 5.9L. when I turn on the AC the air will blow cold for 5-15 seconds and then I will hear a smacking of a door closed, and then I only have heat.
Here's what Ive learned so far: this problem is most likely due to the underbuilt plastic connector between the blend door and the actuator. Although the heater treater youtube video says that all second generation rams have the actuator accessible from outside the plenum/heater core area, this is not the case on my truck. I can find only three actuators: one for the recirc door, one for the control between floor/defrost and dash vents, and one to control between floor and defrost. these all work fine. There is an electric motor mounted on the bottom of the plenum box just above the passenger floor behind the glove box. This I am assuming controls the blend door. when I adjust the heat control, I am able to see the shank of the motor which goes into the plenum spinning. I understand this is shut off electronically when the voltage spikes due to resistance from the door being closed. It currently continuously spins. I put a reference mark on this shank and repetitively watched it turn as I turned on the AC. Every time the smacking noise happened and the heat kicked on that shank was in exactly the same point. I allowed the shank to spin 180 degrees from that point and then disconnected the wiring. I then idled the truck for about ten minutes with the AC running with NO problem. as soon as I started driving, though, the door smacked shut and heat came out. I next took it to get a quote on having a shop repaired it, which was $1000. the next morning, after searching everywhere for some detailed schematic of the inside of the plenum, unsuccessfully(so as to avoid hitting anything inside the plenum), I concluded I would at least try drilling a hole through the plenum and jerry rigging the door on AC for the summer, and promptly drilled right into the heater core (I think, it was a radiator in the plenum which spewed coolant). I epoxied up the knick in the radiator and am currently thinking of connecting the heater hoses together under the hood and bypassing the heater core altogether for the summer.
Any thoughts on whether thats a bad idea? I'd do the job myself if I could, but the manual says under AC it will not give a procedure as its illegal to expell freon into the atmosphere, and most literature online says you must drain the coolant and refrigerant. I have never flushed a radiator before. Is it hard or take anything specialized? What about if I had a shop drain the refrigerant, and then completed the work, or should I just pay the $1000?
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For people in the future, so they avoid the mistake I made, if you are sitting in the passenger seat, all the way to the right is the fan, then next to that is the radiator for the ac. this is installed directly above the low point of the plastic underneath. the low part is angled to a point and then slopes forward into the firewall. to the left of that is where the heater radiator is. This, again, is directly above the low point of the molded plastic below, except for the shape of the lower portion of molded plastic is rectangular at the heater radiator. directly behind the heater radiator is the motor for the blend door. If I was going to drill again I would drill right next to that motor
Last edited by richmonddodge; 07-04-2010 at 05:08 PM..
Go ahead and bypass the heater core. Shouldn't be a problem.
Keep in mind, in order to do repairs on anything inside (and alotta stuff outside....) of the heater box, ya gotta remove it, which requires removing the dash. So, keep that in mind when you are considering when to fix it. (also means discharging the refrigerant from the A/C....)
I too tried to find some GOOD pics of the inside of the heater box. The diagrams in the service manual sucked. I couldn't find any either. If no one else has done so when you tear your apart, would you be so kind as to take some, and post 'em up?
I read here at the forum that another Ram put brass shut off valves on his heater hoses and shut them in the summer time . I was looking at mine today wondering if that would be a good idea. It sounds reasonable, didn't Dodge do that back in the seventies?
Richmonddodge your description matches the symptoms my truck is exeriencing exactly. I've tested out the vaccum and electrical thoroughly and all tested out good. I too hear the door slamming and mine seems to work with the fan on low. But any higher fan settings seems to be too much pressure for the door to hold. Sounds to me like the shaft is slipping on the door. Bypassing the heater core will cut out the heat, but I'm not sure the cold air will make it by. I'll give it a try and let you know, unless you've beat me to it. In the fall I will take my AC/Heater out and take lots of photos (makes it easier to put back together) and post them here. Going to try the bypass idea for now.
Bypassed the heater core with a length of 5/8" heater hose. Works much better, but still not perfect. Considering adding a 5/8" manual heater control valve and a choke style cable for control. Sounds much easier than taking the whole dash apart.
The blend door is powered by a little servo motor. Electrical, not vacuum..... there is a coupler between the motor, and the crank that actually moves the door. As it is plastic, it is prone to failure, and then exhibits EXACTLY the behavior you are describing here. (learned this relatively recently.....) You can actually SEE the motor if you look under your dash, just to the right of the trans tunnel. Its the little doo dad with the electrical connector there. According to popular theory, you can service this peice without having to yank the entire dash/heater box. Just need an angle screwdriver, or, carve a bit of a hole in the padding of your carpet, so you can get at the back screw. There is a company that now makes a METAL coupler for just such an occasion, and someone posted it recently, but, for the life of me, I cannot find that thread again.