I have a 2008 mercury mariner and the heater works great going down the road but when I heat up in morning it blows cold air has antifreeze in it what is the problem ?? Thank you, sherry

SOURCE: 1996 Acura TL Heater blows cold air when stopped

the heater core could be clogged you might again check your coolant level just to be sure its full

SOURCE: Blowing Cold Air

It sounds like you need to do a process of elimination, by following the travel of the hot coolant.

1. Before beginning, safety must come first, so put on a pair of safety glasses/goggles and a pair of gloves.

2.Open the hood and check the coolant level, and add if needed. If you needed to add then recheck for heat after step # 3

3. Close the hood and start and run the engine to normal operating temp.

4."TURN THE ENGINE OFF"

5.Reopen the hood and lightly grasp the top radiator hose feeling for heat caused by hot coolant in the hose. Also feel the bottom radiator hose for heat, (you may have to access the bottom hose from under the car) (while down there look for coolant leak...dripping) If heat is somewhat equal between the two hoses move on. If not there are three areas to check
A) Your thermostat may not be opening
B) Your radiator might be obstructed/clogged
C) Your water pump may not be functioning

6. Locate the two smaller hoses that lead to and from your heater core (a small radiator type device located inside cab under the dash that connects through the firewall) (one is connected at the water pump to the heater core the other is connected at the engine to the heater core) one hose may have a regulator (a small mechanical device operated by either cable,electric,or vacuum that controls the flow of coolant into the heater core) attached inline

7. With the hood raised, restart the engine and adjust the heater control to max heat. Locate a safe area under the hood (free of all moving parts) to access and grasp each of the smaller heater hoses, check for heat, caused by hot coolant in the hose, also check the hose before and after the regulator described in step # 6.
If either of these locations are cold to the touch we can safely say we have narrowed the problem down to one or all of three things.

A) If all heater hoses are cold or only the inlet side of the regulator is hot and the other side is cold or warm, its possible that the regulator is faulty requiring a replacement or is not functioning due to inadequate cable,electric,and/or vacuum to operate it caused by a broken cable, electrical short or disconnected/ broken vacuum line, it also could be a defective (in dash) heater control unit or just a fuse if its electrically operated.

B) If the inlet hose to the heater core is hot and the other outlet hose is cold or warm then its possible that the heater core is obstructed/clogged, requiring a flush out or replacement.

C) If all heater hoses are hot (you may also feel a flow vibration in the hoses) then you should have heat, unless the under dash duct work is disconnected or blower fan is not operating.

I hope this helps.....

SOURCE: 1998 for taurus heater wont blow hot air only cold

you need to check the blend door in the heater box it maybe broken or stuck.the blend door switches between the heater core and ac evaporator to provide a mix of temperature

SOURCE: I have a really strange problem with my Nissan

Since your blower is working and it is a heat issue,thats where we'll start,First thing is have you checked the coolant level in the radiator when engine is cold,make sure it is filled to top,next verify you have coolant in reserve ,Start your van and get it up to normal operation temperature,If your heat gauge on the dash works correctly it should be 190 degrees,Now lift the hood and locate the two heater hoses going into the heater assembly at the fire wall,Both hoses should be hot to hold on to,if both are hot and no heat inside your problem will be the blend air door in heater assembly.
if neither hose is that hot you need to replace the thermostat in the engine to get it up to 195 degrees.
if one hose is hot and one is luke warm then the heater core is blocked and to blame. hope this helps y

SOURCE: 2006 chev silverado heater blowing cold air,

heater core might be clogged

Testimonial: "This worked fine I was thinking I would have to tear the heater apart, the temputure here has been 0 to about 20 THANKS for the help"