AC blows weak

I have a 2007.5 mega with a 6.7. My AC IS INTERMITTENT. When it blows its cold but then it will just quit. When it works It blows weak or sometimes not at all. Any ideas what wrong?

 

Either your evaporator is freezing up or you are low on R134a refrigerant, or both. Correct fix: Have it serviced properly. Cheap and easy fix that is just temporary: Go to Walmart and buy one of those hose/gauge setups for about $20, along with a can of straight R134a (***without leak fixer/sealant***!!!). Get your engine up to operating temperature, park in the shade and leave the engine running. Turn your AC on recirc and crank the fan up to the highest speed. Close the windows, but don't lock yourself out of the truck with the engine running. Connect the Walmart gauge to the low side connection of your AC system (passenger side, below the corner of the windshield) and see what kind of pressure you have and compare it to what it should be with the ambient temperature. The gauge is pretty close to the Dodge specs. If it's low whip out the can of R134a and follow the instructions that came with the gauge. Don't overcharge the system.

One other thing...The cans of R134a now seem to be self sealing, and the old hose/gauge setup won't work. If the ones they are selling aren't made for the new self sealing cans, buy the adapter that is probably right next to the other stuff. It runs about $3.

 

Is the blend door still a problem on the ‘07.5’s like it was on the early 3rd Gens?

 

Evaporator could be stopped up. On the 03-07 3rd gens, you can pull the blower motor and get minimal access to see how much dirt/trash is stuck to the evaporator. I’m not sure you can really get it clean without removal.

As stated above, freeze up is a common problem associated with low freon charge. I think your best bet is someone good at ac work. If the evap is dirty, you will see a false low reading on the quick can and since you aren’t hooked to the high side, you won’t notice an overcharge.

If it were mine, I would check to make sure the evaporator coil isn’t too dirty. Next I would recover the system and recharge by weight.
You could check the coil yourself and then pay for an evac/recharge.

It’s also possible to have blend air door problems, but that’s another discussion and from your initial description, it just sounds like a dirty evaporator to me.

 

A simple test to see if the evaporator is freezing up is to leave the fan blowing but turn off the A/C button. If you start getting cold(er) air and the airflow picks up a little it’s probably freezing up. This is not uncommon here in the south especially on a hot and humid day. It gets worse as the Freon level drops in your system.

 

You can, I did it with a Hoover and a 1/2" soft rubber hose adapted to it to suck everything and all out of the box and from the condenser fins.

Checked progress with my mobiles camera, shooting pics inside the box.

Then I used a spray wand with soapy water to wash out the last debris.

Perfect clean now like new.