dash ac wont work on max

[jdsr]

I dont know if I should post here or workhorse so I'll do both. When I turn max ac on it will blow for a few seconds out of vent and then quit. I think it blows out of defrost instead. Any ideas

 

[jdsr]

I dont know if I should post here or workhorse so I'll do both. When I turn max ac on it will blow for a few seconds out of vent and then quit. I think it blows out of defrost instead. Any ideas

 

[Harry B-THOR]

I have had this problem on a Freightliner chassis. However I think it will manifest itself the same way.

In my case it was a split in a small rubber transition hose that connected a vacuum line made out of nylon to the metal hose connector of a vacuum valve. I would look for that and there are several that controls which way the air will flow. Trace the hoses from your control on the dashboard and you should be able to find out where they go.

 

[Lt46]

Agree with Harry B. The default position for the dash HVAC is defrost. A vacuum leak in most any hose connected to the system will cause it to default. Check all your vacuum lines for cracks and/or rubber degradation.

 

[jdsr]

Thanks for help. I will check tomorrow

 

[Navy Flier]

You have a vacuum leak in the system. Do a search and you will find a number of threads on this problem. I had the same problem in a Horizon and with forum help easily solved the problem.

 

[jdsr]

Just for info. The blue tube controls the max air. Thanks for help

 

[RKL2]

Look at the diaphram valve that opens and shut the vent damper in the black plastic box on the left side of the hood opening...You should see that there is a plastic thin hose which connects to a piece of rubber wiper hose which connects to the diaphram control...I believe the plastic hose is green....Start the engine and listen for the vacuum pump (on the right side of the hood opening ) running...Disconnect the green plastic hose from the rubber connector and plug the green hose with your finger...the vacuum pump should stop running...If it does this is where your vacuum leak is...Get a new piece of rubber wiper hose and connect it to the valve....When there is a vacuum leak here, the damper defaults to defrost position and that is the only vent that works....If this is not the leak, test the rest of the lines by doing the same thing....good luck RKL

 

[NO1RAINH20]

CHECK THE SHORT HOSE HOOKED TO THE DASH POT ON HEATER CONTROL VALVE REMOVE THE METAL ELBOW AND SHOT HOSE AND PLUG LINE BACK ONTO DASH POT