I have a 2001 Dodge Ram 1500 4X4 5.9L automatic. Bought the truck used about a year ago and the A/C wouldn't engage the compressor. I jumped the low side pressure switch which in turn activated the compressor and I added freon 134A synthetic to the system. A/C works beautiful, ice cold, no issues until a few days ago when I noticed the air wasn't blowing out of the vents like it normally does-even on high/max-a/c.
Did my business shutting the truck off for an hour or so in the parking lot here in Florida...........100F! Came back out, fired up the rig and the A/C blowing normally. I'm heading home and I move the blower switch down a notch, all of a sudden I notice the air isn't blowing. Got home and felt the lines under the hood, one hot, one ice cold............pretty much confirmed the A/C was working. After several sessions of this I concluded my evaporator under the dash was freezing up. If I put it in normal A/c so outside air is moving accross the evaporator it doesn't freeze. Never encountered this before so I was wondering if anyone might know what the root cause is? I know the low side pressure switch works as I had to jump it to engage the compressor initially. Can the high side pressure switch be causing the problem? I don't think the evaporator is packed with dirt although I can't be 100% positive because I haven't taken apart the unit which doesn't look to be a 10 minuite job?? Any suggestions??? This truck was a one owner (old timer-never abused) meticiulously maintained truck! It looks like the day it came off the showroom floor. This is what makes me believe the evaporator is not clogged with dirt but then again...............anything is possible.
This issue has nothing to do with the blower motor, resistors, freon or anything else! Read the post and comment only if you know what it is you're talking about! Backyard mechanic want-a-bees need not respond!
WOW! I don't know how to make this any clearer...............THERE IS NOTHING WRONG WITH THE BLOWER, IT BLOWS AIR!!! The PROBLEM is the evaporator FREEZES and when that happens, the blower can't push air through a FROZEN BLOCK OF ICE!!!! WHAT MAKES THE EVAPORATOR FREEZE?????? Simple enough??????.................. PROBLEM: EVAPORATOR FREEZES!!!!...............WHY??????............QUE STION FOR A/C EXPERTS ONLY!!!!!!!!!!! NOT LOOKING FOR OPINIONS.................LOOKING FOR ANSWERS!!!!!!!!!!!!I've been a mechanic for over 35 years, I think I have the opinion part down to a science!

 

I think you can get at least partial access to the evap core, by removing the blower fan, and peeking in there.....

I would think the evap would be more likely to freeze up when circulating outside air, as it is going to carry more moisture than the air already in the cab....... Is your drain hose for the evap core plugged????

 

is there no air blowing at any fan speed? or just on high? if it only blows on the high setting of the fan speed you need a blower motor resister. if the fan works on all speed settings check and make sure you have enough lbs of freon in the system.

 

I picked up on the words "...move the blower switch down a notch, all of a sudden I notice the air isn't blowing". Just last week, my a/c wasn't working on any fan speeds but high. "Crap... Prob'ly the blower motor resistor!" Real easy to get to on the Dodge Ram. It's just under the edge of the glove box. Connector has 4 wires, pull it out, remove two screws... and the resistor block comes straight down. Well guess what!?!? In Dodge's wisdom to NOT include a cabin air filter, when I pulled my resistor out... about a pound of dried leaves came tumbling out of the hole. WTF !!! I used an inspection mirror and peered up into the Evap Coil housing and observed at least that much more leaves clogging the Evap Coil. Spent the next hour with a vacuum cleaner and long flex nozzle just getting that crap out'ta there. The Resistor? Turns out it has a built in protection "device". There's a little copper spring strip that connects two of the leads together. One end is spot welded to one lead, the other end is soldered to the other lead. If the resistor gets too hot, the soldered end melts and the spring tension pops it loose, breaking the circuit. I soldered mine back together and re-installed it. Works great. THAT's when I started looking for a cabin air filter and found that THEY prob'ly didn't make provision for that. Ya know, every bit of that stuff had to have gone thru the blower motor.
Does anyone know how outside air enters the blower box? I have an '02 Dodge OEM repair manual (60MB+ PDF file) and it shows a piece of ductwork that extends forward up into the dash, but no arrows or diagrams describing actually airflow. I've GOT to find where that air comes in because, by gawd, that opening is gonna get filtered even if I end up stuffing a piece of foam rubber into the opening!