2_wacko

iTrader: (2)

My work truck has this problem when at idle it blows hot air but as soon as I start to drive it gets cold. Seems like when the rpms are low it blows hot but when they are high it gets colt. BTW its a 2005 Mack Truck.

EDS01SS

iTrader: (30)

2 possible causes.....condenser is blocked or if you have an electric fan its not coming on

koolaid_kid

iTrader: (21)

Can you look under the hood and see if the compressor clutch is locked at idle?

2_wacko

iTrader: (2)

Its on at idle.

koolaid_kid

iTrader: (21)

Next thing to check is the sight glass (could be on top of the dryer, could be inline with a hose). It should be clear, with no bubbles.

2_wacko

iTrader: (2)

Any other info?

01WS6/tamu

iTrader: (37)

Big trucks use an air actuated fan clutch the fan clutch may not be engaging fully allowing it to pull sufficient air over the condensor for adequate a/c performance at idle. It will get more noticable as the outdoor ambient goes up. Since it cools at highway speed the refrigerant charge is very close. Check for the clutch not locking it should roar and pull a signficant amount of air if you engage the high idle, or check for bugs blocking the condensor.