Heat blows cold air when stopped

[NJExplorerFan]

I hope someone can help me. When I'm running the heat on in my '03 Explorer, it suddenly starts blowing cold air when I come to a traffic stop. Then when I start driving again, the heat comes back. What the heck is this?

 

[BigAl90]

I would suggest checking to see if the heater core is clogged. That may be the reason you are running into this issue.

 

[5whiskey]

So you have heat when you're driving, but at idle it begins to blow cold air? Most of the time this is a sign of low coolant.

 

[hillre51]

I have a 2003 Explorer doing the same thing. I plan to replace my heat control valve after testing the coolant. My thermostat is good supposedly. The upper radiator hose is hot and both heater core hoses. Spouse keep complaining about cold air on legs.

 

[D Hook]

I have a 2003 Explorer doing the same thing. I plan to replace my heat control valve after testing the coolant. My thermostat is good supposedly. The upper radiator hose is hot and both heater core hoses. Spouse keep complaining about cold air on legs.

Are you getting heat anywhere in the vehicle?

 

[lincolnshibuya]

if you have the digital climate control try running the self test diagnostic first,

http://www.explorerforum.com/forums/showpost.php?p=2095985&postcount=81

the digital climate control uses the engine speed to control the vacuum lines which operates the doors/actuator to maintain temp in AUTO mode. one of those vacuum lines control the heater valve switch. the heater control valve closes so that hot coolant will not go through the heater core.

also does it do the same thing when not in AUTO mode?

 

[NJExplorerFan]

I am getting heat but only when the truck is moving. It's a manual climate control system.

 

[rocket22]

MY thought is low coolant, bleed/burp system

Trapped air?

 

[5whiskey]

Trapped air?

I thought about this too... it could be that if the coolant level shows normal.

 

[Turdle]

Heater going cold at idle is almost always caused by low coolant level. Checking just the overflow , or reservoir might not give a true indication of what is in the system because the overflow tube often gets clogged, and does not allow coolant back into the radiator.

Park on an uphill incline or raise the front of the vehicle up about a foot, let cool then check the coolant in the radiator. Refill thru the radiator cap with engine running and heater set to hot and vent function set to floor.

 

[hillre51]

Yes, I'm getting hear all over when first driving vehicle. It seems to blow cold air after driving for a while...........while stop at red light and while driving after taking off from red light. very weird situation. How on earth would a person know if a heater core is clogged or not? If it's clogged, wouldn't the vehicle run hot? Thanks

Are you getting heat anywhere in the vehicle?

 

[hillre51]

Thanks for the info, I will run the self test. I didn't even know you could do that). Where is the heat control switch located and how would one determine if it's faulty or not? Voltmeter? If so, how?

I normally don't run mine on "Auto" but will try it that way. I normally just push the air flow for the vent/floor.

very strange situation......................heater get so hot during first 20 minutes of driving, that a person can hardly stay in it. I normally run mine at 74 or 75. seems turning the thermostat up higher works but isn't hot as should be at those temps...........78+.

Appreciate the info.........will run self test and let you know in couple days.

thanks

if you have the digital climate control try running the self test diagnostic first,

http://www.explorerforum.com/forums/showpost.php?p=2095985&postcount=81

the digital climate control uses the engine speed to control the vacuum lines which operates the doors/actuator to maintain temp in AUTO mode. one of those vacuum lines control the heater valve switch. the heater control valve closes so that hot coolant will not go through the heater core.

also does it do the same thing when not in AUTO mode?

 

[hillre51]

How would an overflow tube get clogged by the way? Never had that issue in 40 years.

I will perform the uphill task and or lift vehicle up.

I don't recall seeing a radiator cap on my 2003 explorer 4.0. Identifying the radiator cap is usually a given.

When I flushed mine a few years ago, I filled it via the reservoir. Suppose I could drain some of the antifreeze and run engine to see if antifreeze in reservoir transport to radiator.

I'll be back with with outcome on this test as well.

Heater going cold at idle is almost always caused by low coolant level. Checking just the overflow , or reservoir might not give a true indication of what is in the system because the overflow tube often gets clogged, and does not allow coolant back into the radiator.
Park on an uphill incline or raise the front of the vehicle up about a foot, let cool then check the coolant in the radiator. Refill thru the radiator cap with engine running and heater set to hot and vent function set to floor.

 

[hillre51]

Are your hoses getting hot (upper radiator/heater core)? Is engine full of coolant? Mine is doing just the opposite intermittently............it burns you up during first 20 minutes or so, at speeds under 50 mph or less. very strange

I hope someone can help me. When I'm running the heat on in my '03 Explorer, it suddenly starts blowing cold air when I come to a traffic stop. Then when I start driving again, the heat comes back. What the heck is this?

 

[hillre51]

If the coolant is low, shouldn't the low coolant sensor illuminate while driving it? that's if it is properly working.

Heater going cold at idle is almost always caused by low coolant level. Checking just the overflow , or reservoir might not give a true indication of what is in the system because the overflow tube often gets clogged, and does not allow coolant back into the radiator.

Park on an uphill incline or raise the front of the vehicle up about a foot, let cool then check the coolant in the radiator. Refill thru the radiator cap with engine running and heater set to hot and vent function set to floor.

 

[hillre51]

So how would a guy get rid of trapped air or confirm it's the situation?

Trapped air?

 

[hillre51]

Can you tell me what type of scan tool to use? I only have an Actron. Or are you referring to the scan tools use by auto shops for diagnostics?

if you have the digital climate control try running the self test diagnostic first,

http://www.explorerforum.com/forums/showpost.php?p=2095985&postcount=81

the digital climate control uses the engine speed to control the vacuum lines which operates the doors/actuator to maintain temp in AUTO mode. one of those vacuum lines control the heater valve switch. the heater control valve closes so that hot coolant will not go through the heater core.

also does it do the same thing when not in AUTO mode?

 

[Turdle]

If the coolant is low, shouldn't the low coolant sensor illuminate while driving it? that's if it is properly working.

There is no "low coolant" sensor, but there is a temp "gauge" sender . It will not be accurate if there is no coolant in contact with it.

How would an overflow tube get clogged by the way? Never had that issue in 40 years.

The overflow outlet is at the bottom. Any sediment in the cooling system can settle there and clog the tube when coolant tries to flow back into the radiator.

 

[hillre51]

Alright, thanks for the info, i will disconnect it and run water through to see if it's clogged or not.

There is no "low coolant" sensor, but there is a temp "gauge" sender . It will not be accurate if there is no coolant in contact with it.



The overflow outlet is at the bottom. Any sediment in the cooling system can settle there and clog the tube when coolant tries to flow back into the radiator.

 

[jhanan]

I am getting heat but only when the truck is moving. It's a manual climate control system.

I have exact same problem (posted a couple weeks ago here). My coolant was low and filled it up. It is better but still seems to be an issue. Also replaced the blower and the fan resistor.