I have a 2004 Ford Explorer with a V6 and the heat only works when engine is accelerating.... the temperature is gauge reads fine and the blower works fine as well..... otherwise I got cold air.... any ideas

 

1.The cooling system IS full of coolant, isn't it?

2.Allow the vehicle to heat up with the HVAC controls set to "Heat" and temperature selector set to "Hot", blower on. When vehicle is at operating temperature feel the heater hoses. Are they both similarly hot or one hot/one cold? If the heater core is partially stopped up one will be hot, one cold/much cooler.

3. If the cooling system is full and both heater hoses are hot then you must have a vacuum issue.That can be a broken/leaking vacuum line or a defective selector control. Make a visual inspection of the small plastic vacuum lines under the hood and see if they're all connected and in good condition. You didn't say if you had the Manual or the Dual Automatic Temperature Control system. Post the answers to theses checks and we can go from there.

 

It sounds like you have an air pocket in the cooling system and the reason you have heat under acceleration is inertia is causing the coolant to flow to the heater under acceleration. If there is a bleed valve in the system you may be able to evacuate the air, otherwise try loosening a hose that is topmost in the engine compartment. If you get air out you will have found your problem. This often happens after a cooling system service or thermostadt change.
Good luck with it.

 

it is like a it needs to be burped, air pocket, right?

 

In my opinion.