Question about 2003 Nissan Sentra

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Heater works good then all at once starts blowing cold air

Flushed system checked thermostat pulled radio out to check butterfly flap to see if opening and closing

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You will have to replace the thermostat...It sounds like the thermostat is not opening and closing all the way. When the car is running fast enough to heat up the water, great...heat...but at stops the thermostat is not closing all the way allowing the water to cool as it passes through the heater.

Posted on Nov 08, 2008

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As i described a few minutes ago about a 1992 olds cutluss 3.1 v6. System has been bled. new thermostat also...both hoses upper and lower are hot....circulation is good but only blows cold air


I need more info. When you set the vent control to defrost does it direct the air to the windshield. and when you set it to floor does it go there. if yes the control to divert air is working. before replacing the control unit you need to find the lines that feed hot water to the heater and check to see if line coming in to the heater is hot and the line returning from the heater is warm to hot. sometime the heater gets plug. if so just disconnect the lines to the heater and flow water from your garden hose to the return line of the heater for about a minute or so this will flush dirt from the heater. reattach the lines and check for heat. This is a known problem for all cars as they get old.

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My truck starts running hot then I turn the heater on and it blows cold air but every once in a while the heater will throw out hot air. Then the temp gauge will go down. I've check med the radiator cap...


I'd still check the thermostat. Or basically just replace it. Have you ever drained all the antifreeze and flushed the system? Good time to do both. If the hose's get real hot that doesn't really mean the thermostat open. Wouldn't they get hot even if the thermostat didnt open.? If the thermostat was stuck open you'd would have cold air and low temp gauge. Then maybe hit a pump or something and have the thermostat stick closed and have high temp. Maybe water pump. Check it when you have the belt off. Spin, pull & push the water pump pulley around. I'd replaced my water pump at about 110,000 on a '97 dodge Dakota. My 97 never had a very good heater. Always heated up more after driving. Idle never got it warmed up.

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you may have a blocked heater core. you can try flushing cooling system if that doesnt work replace heater core.

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2 Answers

Heater only blows worm air not hot


Check these three possibilities: One, car has a bad thermostat. Two: Car has a bad heater control valve and three: Car has a vac leak under the dash that controls the heater Flap Valve. If this flapper isn't closed completely, cool outside air mixes with the warm inside (recirculating) air and cause a lukewarm air mixture at the vents.

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1 Answer

Heater will not blow hot air. it blows cold air and fan blows. new thermostat and full radiator


The heater core is possibly blocked or the temperature adjuster is not working.

First check the controls to be certain that the temperature aduster is working and the flaps/doors that direct the flow of hot air are working.

If they are..........

Check heater hose temp. If one is hot and one is cold, you are not getting flow through the heater core.

Bleed it to remove an air blockage.
If that does not work, flush the system.
If that does not work, replace the heater core.

Karl at topgunwon.com

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No heat, blows cold air, flushed system, then a day later blew radiator, changed that still no heat... one mechanic said its the blender box? any suggestions will help...


I would check the heater tap in the heater hose, this may be blocking the flow. {causing excess pressure It could also be possible that the heater cable may have come off the back of the control or off the heater flap on the box. lastly, replace the $8 engine thermostat. You can also test it in a glass of boiling water and watch to see if it opens. Good luck.

Nov 19, 2009 | 1998 Chevrolet Blazer

1 Answer

No heat air is blowing cold


First you have to identify what causes the problem.
To do this you have to:
1) When engine is cold check the level of coolant. If it is low fill it up.
2) Start engine and check if engine reaches regular temperature. If your engine is not heated enough it means your thermostat does not work properly and should be replaced.
3) If engine temperature is normal, then check the temperature of pipes that go to/from heater core. These pipes are located up the fire wall (easier access is from the passenger side). If pipe/pipes are cold (even engine is worm) it means you heater core is plugged and should be flushed. Keep in mind, flushing the whole cooling system is different from flushing heater core.
4) If pipe/pipes are hot/warm, turn off the fan, switch controller to the hot position, wait for 3-4 minutes and turn on the fan. Note if the cold air blows first or warm air blows first but it cools down in 5-10 seconds. If the air blows cold than it is most probably the problem with blend door or blend door actuator.
5) If air blows warm first and then cools down, then while running engine and remaining the transmission in PARKING position, press on the gas pedal until your engine reaches 3,000 RPM. Check if your heater blows warm/hot air. If it does, then your water pump does not work properly and should be replaced. If the air still cold, I would suggest to flush the heater core.

Oct 22, 2009 | 1998 Ford Taurus

1 Answer

Heater not working


First you have to identify what causes the problem.
To do this you have to:
1) When engine is cold check the level of coolant. If it is low fill it up.
2) Start engine and check if engine reaches regular temperature. If your engine is not heated enough it means your thermostat does not work properly and should be replaced.
3) If engine temperature is normal, then check the temperature of pipes that go to/from heater core. These pipes are located up the fire wall (easier access is from the passenger side). If pipe/pipes are cold (even engine is warm) it means you heater core is plugged and should be flushed. Keep in mind, flushing the whole cooling system is different from flushing heater core.
4) If pipe/pipes are hot/warm, turn off the fan, switch controller to the hot position, wait for 3-4 minutes and turn on the fan. Note if the cold air blows first or warm air blows first but it cools down in 5-10 seconds. If the air blows cold than it is most probably the problem with blend door or blend door actuator.
5) If air blows warm first and then cools down, then while running engine and remaining the transmission in PARKING position, press on the gas pedal until your engine reaches 3,000 RPM. Check if your heater blows warm/hot air. If it does, then your water pump does not work properly and should be replaced. If the air still cold, I would suggest flushing the heater core.

Oct 17, 2009 | 1998 Ford Taurus

2 Answers

Heater blows cold air, replaced thermostat &


try to back flush the heater core. and if that dont work check the blend door it see if it is working.

Oct 15, 2009 | 2002 Mitsubishi Galant

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