04 gmc sierra heater issues

I have a 2004 gmc sierra and it is having heater issues. For a while now when starting it up cold it would not blow any warm air until the vehicle is moving. The other day while driving it would go back and forth between hot and cold. Any ideas what the problem is?

I have a 2004 gmc sierra and it is having heater issues. For a while now when starting it up cold it would not blow any warm air until the vehicle is moving. The other day while driving it would go back and forth between hot and cold. Any ideas what the problem is?

Have you checked the coolant level in the radiator? Low coolant will cause this.

I have a 2004 gmc sierra and it is having heater issues. For a while now when starting it up cold it would not blow any warm air until the vehicle is moving. The other day while driving it would go back and forth between hot and cold. Any ideas what the problem is?

Had the same thing last year... I checked fluid and it was low... Found out one of my hoses had a slow leak. Once I topped off the fluid it was nice and cozy again!

If you are low on fluid.... Make sure you let the truck idle up to temp as the thermostat has to be open to draw in the right amount of coolant.

yup low on coolant. Go head and flush system out. Dexcool turns acidic when it gets low. Trust me.