A/C Guru needed! Help! Help!

From : cmdr dave

Q: hello all i have a 95 dodge 2500 4x4 diesel. the air conditioner worked half assed for about a week and then quit. clutch is engaged. tubing going into firewall are both quite cold with little temp difference between them. i have a recharge kit with a gauge so i hooked it up and pressure was around 45 which the gauge says is fine. so then i started doing my creative snooping around. i started feeling around under the dash. part of the plastic housing was cool. there was the stub end of a shaft sticking out of the bottom of the plastic housing. i think it is a pivot shaft for some kind of door. i put a pair of vice grips on it and rotated about 60 degrees or so. i now have a/c coming out of the panel ducts. i also have warm not hot air coming out of some ducts at the bottom of the plastic housing. i believe these are the ducts that hot air come out when you have the controls on heat to the feet. last part of my observations. i looked in the engine compartment and saw no obviously loose vacuum lines. lastly when you do the switch that tells the air where to go like to defrost panel etc. the air is re-routed in 1-2 seconds to where you just told it to go. in other words no real delay. i have come to the conclusion that little doors that are supposed to open and close in the heater housing are not doing their job. here are a few questions. do they open and close with vacuum or electrical solenoid. i cant even begin to find a way to climb into the plastic heat/ac housing. im looking for any guidance that somebody wants to throw at me. thanks for the help...dave .

Replies:

From : tom lawrence

i have come to the conclusion that little doors that are supposed to open and close in the heater housing are not doing their job. here are a few questions. do they open and close with vacuum or electrical solenoid. the diverter door which controls which vents the air blows through is controlled via a vacuum motor. it sounds like this is working correctly. the blend air door which controls how much air flows across the heater core air always blows through the a/c evaporator no matter what is controlled mechanically via a cable attached to your heater controls. the door has a spring on it to return to the full hot position. cant even begin to find a way to climb into the plastic heat/ac housing. im looking for any guidance that somebody wants to throw at me. yeah unfortunately there isnt. if something in the hvac unit needs fixing you have to remove the dash to get to it. however try something easier - remove the dash bezel two screws inside the cupholder two more in the ashtray then remove the heater controls. check the steel cable on the back of it. disconnect it from the controls and give it a tug. see if the doors stuck or if the cables come loose. you may not be able to fix it from here but at least youll get a better idea of whats wrong. .

From : cmdr dave

i have come to the conclusion that little doors that are supposed to open and close in the heater housing are not doing their job. here are a few questions. do they open and close with vacuum or electrical solenoid. the diverter door which controls which vents the air blows through is controlled via a vacuum motor. it sounds like this is working correctly. the blend air door which controls how much air flows across the heater core air always blows through the a/c evaporator no matter what is controlled mechanically via a cable attached to your heater controls. the door has a spring on it to return to the full hot position. cant even begin to find a way to climb into the plastic heat/ac housing. im looking for any guidance that somebody wants to throw at me. yeah unfortunately there isnt. if something in the hvac unit needs fixing you have to remove the dash to get to it. however try something easier - remove the dash bezel two screws inside the cupholder two more in the ashtray then remove the heater controls. check the steel cable on the back of it. disconnect it from the controls and give it a tug. see if the doors stuck or if the cables come loose. you may not be able to fix it from here but at least youll get a better idea of whats wrong. hello tom thanks for the great input! ill do as you suggested this evening. anyone ever see a cut-away drawing of the hvac unit i would be interested in looking at that. i wonder what the shop time/ charge is for dodge to tear the dash apart and fix well...at least with the vice grips i have ac now. of course having a pair of vice grips hanging of your hvac unit doesnt really look like your on top of things! lol! again thanks for the help...dave .

From : tom lawrence

ever see a cut-away drawing of the hvac unit i would be interested in looking at that. i can scan a couple of diagrams out of a service manual for you but its really pretty straight forward. you have a recirc. diverter door at the intake which allows air from either the outside or from the cab to get sucked in by the blower motor which is a simple squirrel-cage blower. in front of the blower is the blend air door which closes off either the direct passage to the heater core the passage that bypasses the heater core or some position in-between. just before the outlet is the a/c evaporator and an the outlet you have the diverter door that directs the air into one of three separate ducts - floor dash or defrost or positions in-between. again both the recirc. and diverter doors are operated by vacuum motors and the blend air door is mechanical. i wonder what the shop time/ charge is for dodge to tear the dash apart and fix its close to an all-day affair. figure 6 hours of time plus parts. the first time i had my a/c evaporator leak on my 95 ram i did all the work to remove the dash then drove it to the mechanic had him do the actual removal of the hvac unit and swap the evap. then took it back and re-installed the dash. saved a bunch of money doing this. when my heater core in my 99 let loose i dropped it off at the shop and said have fun. it wasnt an experience i wanted to repeat .