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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29534
Experience:  GM Grand Master Technician 2007. 14 years experience.
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2005 Chevy: intermittent..It blows cold air..heat at 70 mph..slow down

Customer Question

My 2005 Chevy Silverado only has intermittent heat. It blows cold air during idle, but starts blowing heat at 70 mph. If I slow down, I get cold air again. It was low on Anti-Freeze, added some, still no heat. I checked hoses going into heater core, in was hot, out was cold.
Submitted: 7 years ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 7 years ago.
Welcome. This sounds like either you still have a low coolant condition or the heater core is plugged. What I would do is take both lines off and put high pressure water in the cold line to try and flush out the restriction.
Customer: replied 7 years ago.
How do I put high pressure water in the core?
Expert:  GM Tech (Cam) replied 7 years ago.
Take the lines off and use a car wash want or even your garden hose.
Customer: replied 7 years ago.
Should I drain all of the coolant first?
Expert:  GM Tech (Cam) replied 7 years ago.
No, just take those 2 lines off.