Air system not operating correctly 2005 Volvo.

You did not state Primary or Secondary air. only front and rear tanks.

What is your primary air doing and what is your secondary air doing.

Your compressor does not adequatly fill your air system at idle. That's a problem which needs a remedy from a mechanic. Your overall top pressures between 100-120 is adequate. I prefer both to be at or over 120 if at all possible and the Compressor have enough lungs to fill those tanks almost as fast as I can use up the air.

120 psi in either or both primary and secondary air supply will drain to 40 in a hurry if I need to.

 

Ok, your truck is not functioning properly at the air compressor. You should be able to fill to max on your tanks provided you had adequate atmosphere, altitude and so on.

I have never had a truck fail to completely and adequately fill both Primary and Secondary at idle and keep it there.

Second. There is a little too much difference between 100 and 120. It's not BAAAD... but most of my trucks again will fill to within a handful of digits apart.

 

Have you checked or replaced main charge line? Some times they will bleed air as they get older and harder

 

Did you have this problem before you changed these parts?