Is there more then one place to replace AC refrigerant, 379 with sleeper

You need to look at the center of the ac compressor to see if it's turning then its on if not spinning then its off when you get it nearly full of freon it will start to cut off and on and the fan will start turning turning on and off when its nearly full of freon so you know it's about full of freon.

 

I have a '91 379, 3406b. I was told that there is a completely separate a/c unit under the bed in the sleeper. I can access mine from the passenger side door. I havent bothered to test or use it as Im a local driver. Check the lines in the side box and under the sleeper in the immediate area.

 

your truck has 2 ac units but it's all ONE system..
1 compressor runs all if it...

 

Should be 2 ports. Low pressure and high pressure.

Never worked on a truck with a sleeper before but have always been told its just one system but with an extra evap core and blower in the sleeper.

 

Have you checked the cab and sleeper air filters to see if they are clean? Are you running the A/C on fresh or recirculated air? Is the fresh air door stuck open ( located behind the air breather on the passenger side of most 379 Peterbilts. Yes it makes a difference. The clutch fan should come on when you turn the A/C on as the head pressure rises.
There are separate units for the cab and the sleeper BUT they are one closed system with only one set of ports for running a vacuum and adding Freon.
Save time , momney and aggravation and go to a reputable dealer and WATCH them as they work on it so you can learn something.

 

I've never noticed a filter in the bunk A/C unit, just in the cab. Is there one in the bunk?

 

yes

 

Yes but most people don't know that.