no heat

i have a 2000 impala ls when iam driving my heat blows cold but when i come to a stop it goes back to hot air. i replaced my thermostat and flushed the system and put new antifreez in and replaced my cabin filter. still no luck
does anybody know the fix.

i have a 2000 impala ls when iam driving my heat blows cold but when i come to a stop it goes back to hot air. i replaced my thermostat and flushed the system and put new antifreez in and replaced my cabin filter. still no luck
does anybody know the fix.

If vacume controls on heater you need to check vacume lines and or vacume reserve tank. It may be losing vacume.
MT

If vacume controls on heater you need to check vacume lines and or vacume reserve tank. It may be losing vacume.
MT
ok i will try that thank you

ok i will try that thank you
i checked all the vacume hoses all ok any other idea

i checked all the vacume hoses all ok any other idea

Make sure engine tempt is holding good driving.
Rad full of coolant.
Does heater hoses feel hot when you speed engine up?
Does everything work good when parkeed or sitting still?
Good hot heat then?
Switching good from hot to cold?
Dual controls?
AC and heater and defrost switching good at the right vents?
If so it still sounds like vacume lose someplace.
MT

If your car has the 3400, there is a special coolant bleed prceedure to get the air out of the cooling system. That is what it sounds like is your issue to me.