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First, its a Sterling... you're gonna regret that purchase. Daimler A.G. claimed they'd continue supporting them for 10 years after they ended production in 2009, but they've been lacking in that, especially since Ford still supplies wiring harnesses and some other components, and they made no such obligation to continue supporting them. So, best of luck to you with that purchase... hate to say it, but they were better when Ford made them. Sorry to be a doomsayer, but I'm a mechanic with a municipality which has a bunch of Sterlings, and I was a driver and equipment operator for ten years before becoming a wrench, and I literally hate Sterlings with every fiber of my being. Anyhow, to the point..First, check your coolant level. Sounds pretty elementary, I know, but just check it. Top it off as needed, see if that rectifies the problem. If not, check to make sure the lines to the heater core don't have a cutoff valve which is shut off. Drivers often do this during the warmer months because it can get the AC a couple degrees cooler... or else it can make the AC work when the heater control valve goes tits up (remember what I said about Daimler crapping out on supporting those models for ten more years? Yeah...). Exactly how they're routed... depends on your model year and which engine you have. Detroit Diesel, Mercedes-Benz (from 2003 up), Cummins, and Caterpillar engines were all available in Sterling products, as well as one Mitsubishi engine (because the 360 was just a badge engineered Mitsubishi Fuso, and you never said what model Sterling you had). If the valves to the heater core are open or else aren't installed, check the temperatures of the lines to the heater core once the vehicle has been running, the thermostat has opened up, and the coolant is hot. If one of those lines is cold, you have a plugged heater core. If they're both hot, you're probably looking at a blend door issue.

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Q: Why does sterling truck heater only blow cold air?
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Why would a Sterling Semi truck heater only blow cold air?

Could be a number of reasons. Low coolant would be my first suspect, although most motors offered in a Sterling would shut down if the coolant got low. The heater core could be bad, there could be blockage in the heating system somewhere, you might have a bad or blocked heater hose.

Why does your heater blow cold air in your truck?

Low on coolant. Stuck open thermostat. Plugged heater core. Faulty temp blend door.

How will the heater react if the heater core is stopped up?

Your heater will blow cold air only.

Why would a house heater blow out cold air?

It doesn't really blow it out it just warms the cold air.

Why does your truck blow cold air?

Assuming you want it to blow hot air, you may be low on coolant or have a stuck open thermostat or a plugged heater core or you have a faulty temperature blend door actuator.

On a 1995 Gmc sierra truck why does the air conditioning vents on dash work in every mode except cold air cold air will only blow out from floor vents?

The a/c - heater controller is out...........

Why does the heater blow heat while driving and cold at idle?

you need to replace your heater core

How can you tell if heater blower is not working?

it wont blow heat itll blow cold air

In your truck when you switch from cold air to heat the air still blows cold?

Interior heat uses the engine heat. If the engine is still cold, the heater will blow cold. If the engine is warm and the heater is blowing cold, you have a problem with the heater. Check the water in the radiator and see if it is rusty. If it is rusty, change your coolant, thermostat, and hoses. Look at the heater hoses when someone steps down on the gas pedal. If a hose collapses, replace your heater hoses. Otherwise take it to a mechanic.

Why does Kia Sorento heater blow cold air?

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Why would you smell antifreeze and heater blow cold air?

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