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Blend door actuator is electronically controlled. Thermostat changed and fluids good. One of the hoses going to heater core is hotter than the other the one coming from the engine block.

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The supply of coolant to the heater is ok, one very hot and one not so much indicates normal heater operation. You have an air temperature control blend door problem it is mostly jammed and this has ruined the motor actuator.

Posted on Dec 03, 2016

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Posted on Jan 02, 2017

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I changed thermostat on 2005 buick rendevous ultra 3.6l. still have no heat. whats next?


Was lack of heat in the cabin the only reason you changed the thermostat? Were the radiator hoses hot (or very warm) to the touch before you changed the thermostat? Were the heater hoses hot before you changed the thermostat? Did you get a check engine light and code stating that the engine was not getting (or slow getting) to operating temperature?
Getting heat from your heater depends on a blend door actuator letting air flow through the heater core in the HVAC unit. If your radiator hoses are hot, your heater hoses are hot, and you have no trouble code indicating the engine is not getting to operating temperature, but you are not getting heat inside the car, you need to check your blend door actuator or the control unit for the heater.

Jan 08, 2017 | 2005 Buick Rendezvous AWD

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Heat troubleshooting


<span>There are a few reasons this might happen to your system.<span> </span>A typical system is shown in the diagram below:<span> </span></span><br /><br /><br /><img src="CC87E1A.jpg" /><br /><br />The system requires hot water from the engine to pass through the heater core and the blend (or mix) door positioned for air pushed by the blower motor to pass through the core.<span> </span>If the <a href="/../cars/r6235876-no_heat_fan_blowing_cold_air#">vehicle</a> has no air conditioning, the evaporator is absent from the system.<span> </span>Some designs also incorporate a control valve in the heater hose to stop coolant flow to the heater core when not in use. The blend door position is actuated by a stepper motor or cable.<br />Typical failure modes are as follows:<br /><span><span>1.<span> </span></span></span>Blend door stuck<br /><span><span>2.<span> </span></span></span>Blend door actuator failed motor or stripped gears<br />3. Blend door cable is broke or needs adjustment<br /><span><span>4.<span> </span></span></span>Temperature control switch failed<br /><span><span>5.<span> </span></span></span>Air pockets in engine cooling system<br /><span><span>6.<span> </span></span></span>Clogged heater core<br /><span><span>7.<span> </span></span></span>Heater coolant control valve failed closed<br />8. Thermostat failed open<br /><br /><b>Troubleshooting:</b><br />First, with your engine hot and the heater turned on, feel the heater hoses in the engine compartment as they attach to the heater core at the firewall.<span> </span>If either of the hoses is cold, the problem is likely a lack of adequate coolant flow.<span> </span><br /><br /><b>No or low coolant flow:<span> </span></b><br />Check for the presence of a control valve in one of the heater hoses--trace the hoses all the way to the engine.<span> </span>Not all vehicles have such valves.<span> </span>If you find one, check to see if it is actuating properly.<span> </span>It should receive a signal of some kind from the heater controls and open when the temperature control is turned to heat.<span> </span>If you cannot determine that the valve is opening, try taking one of the clamps off and removing the hose to see inside the valve. A typical vacuum operated heater flow control valve is shown below:<br /><br /><img src="7FA590D.jpg" /> <br /><br />The valve may also be actuated by a solenoid or wire cable. <br />If you have no valve, next check the cooling system for air. If you have a radiator cap, take it off and look inside.<span> </span>If it is not full, fill it with coolant and start the engine.<span> </span>Turn the heater on and let the engine run until it is warm and the thermostat has opened.<span> </span>Continue to fill the radiator or reservoir until the level stops falling.<span> </span>Check for the presence of any bleed ports in the system.<span> </span>Bleed ports may be on the housings that radiator or heater hoses attach to or may be installed in the hoses themselves.<span> </span>A typical Honda application is shown below:<br /><br /><img src="C655B97.jpg" /><br /><br />For stubborn cases, p<span>ark the <a href="/../#">car</a> uphill, take cap off radiator, start <a href="/../cars/r6235876-no_heat_fan_blowing_cold_air#">car</a>, fill radiator, let it warm up until <a href="/../#">thermostat</a> opens, bleed air out, fill to the neck of the radiator and watch for bubbles coming up. Once you have bled the air, if gas continues to come out, you may have a blown head gasket that is forming bubbles that can block coolant from entering the heater. In these cases, the heater may work well at speed but blow cold at idle.</span><br /><br />Clogged core: If the control valve is open and there is no air in the system, your heater core may be clogged.<span> A quick way to check for a clogged core is to turn the blower motor off for a while and then back on. If it produces warm air for only a short time and then cools down, your core is only passing a small amount of coolant. This can also be caused by a bad control valve, if you car has one or possibly by a weak water pump. </span>You can try flushing the core by removing the heater hoses and attaching a garden hose or other source of water pressure to force water through the core.<span> </span>Use an adapter to make a good seal and connect to the lower pipe to backflush the core.<span> </span>If the core will not flush or allow adequate flow, replace the heater core.<br /><br />Thermostat: if your car temperature is running cold and only warms up when idling, the heater will do the same. This is caused by a thermostat that has failed open, allowing too much coolant to flow through the radiator. <span>.</span><br /><br /><b>Blend door not moving to heat position:</b><br />If you have coolant flow through the heater core, the problem is with the blend door.<span> </span>The blend door is almost always actuated from under the dashboard.<span> </span>Many systems use an electric motor to actuate the blend door.<span> </span>Check any heater or A/C fuses before tearing into your system.<span> </span>You may need to remove a partition to see the actuator.<span> </span>The door should be to the right of center under the dash.<span> </span>A typical electric motor actuator design is shown below.<br /><br /><img src="4ED4FC8.jpg" /> <br /><br />The actuator can be on the top front or bottom of the duct.<span> </span>Consult a manual for your vehicle if you cannot locate the actuator.<span> </span>Once you can see the actuator, watch it while you change the temperature setting (key on unless it is cable operated).<span> </span>If the actuator doesn't move or turn, troubleshoot the reason.<span> </span>Systems such as the one in the above picture typically fail in the shaft attach or the internal gears on the actuator.<span> </span>If your actuator is getting power but not moving the door, replace the actuator.<span> </span>If the actuator is not getting power, troubleshoot the control switch.<span> </span>Due to the wide variety of designs, we cannot provide test tips for electric blend door control switches.<br />Whether your blend door is electric or cable operated, remove the actuator and operate the door with your hand.<span> </span>If the door sticks, the heater box must be removed and opened to free the door and restore unhindered operation.<br />If your blend door is cable operated, check the cable for proper attachment at the control lever and at the door lever.<span> </span>The cable sheath must be properly adjusted and firmly clamped for proper operation.<span> </span>To adjust, first remove the cable from the door and move the door lever with your hand to observe the range of motion.<span> </span>Then set the control to full hot, open the door fully, and reattach the cable, clamping the sheath so as to ensure the door opens fully when set to hot.<br />

on Jan 31, 2011 | Dodge Caravan Cars & Trucks

3 Answers

My heater stoped working the a\c still works and fuses are fine


Either the heater core is clogged or busted, or a blend door is broken.
YOU TUBE has a lot of videos on this subject.

Jan 28, 2016 | 1998 Ford Expedition

1 Answer

'94 Ford Taurus-No Heat?


Good point. Solving it will probably take more time than money.
Thermostats and heater cores do not work one day and stop the next. If your engine warms up normally and doesn't overheat, the gauge reads normally, engine is at normal operating temperature after about 10-15 minutes ...all these point to a good thermostat. It is working right and should not be a problem.
To check the heater core, wait till engine is at normal operating temperature. Turn heat setting to high, then feel both heater hoses-both should be hot. If both are hot the core is circulating coolant and is not a problem. If only one is hot (which would be the inlet hose) the core is not circulating-could be an air block or the core is plugged up and will need replacing.
If heater core and thermostat are good, then it probably is the temperature blend door in the heater case. The door actuator is probably vacuum controlled. I don't know how difficult it is to troubleshoot on your Taurus, but check if vacuum controls are working right from the dash controls, check if the blend door is stuck, is broken, or if the vacuum control is working to open and close the blend door. When you want heat, the blend door should let blower air pass across the heater core.
From the engine you will have a single vacuum hose that goes through the firewall into the dash to the heater/AC controls. There, a pod like device can rout the vacuum signal to various doors on the heater case.
Good luck.

Jan 07, 2014 | Cars & Trucks

1 Answer

Have tried replacing thermostat , Flushed out heater core , Fluid level is fine temp running around 196 to198 f Still no heat inside car


Either the heater core is plugged up or the temperature blend door is not functioning properly. With the engine running at operating temperature, Feel the hoses that go to the heater core. Are they both hot to the touch? If one hose is noticeably cooler then the other one, then a bad heater core is indicated. If the hoses are both hot, then check the operation of the temperature blend door.
1. Remove the passenger side lower dash board trim panel.
2. Attempt to locate the blend door actuator.
On older cars, this was usually a cable operated device. Most newer cars use a vacuum operated actuator valve. Operate the temperature control while observing this device. If no movement is detected, then the actuator is bad or the temperature control itself is bad.
Make sure all the air is bled out of the system after performing cooling system service. If it is a newer vehicle, then look for coolant air bleeds on the engine near the thermostat housing. Air might become trapped inside the heater core reducing the amount of heat produced during operation. I hope this information is helpful to you and thank you for using Fixya.com.

Jun 02, 2011 | Buick Park Avenue Cars & Trucks

2 Answers

No heat from my heater. Fluid levels are good, motor seems slow to heat ( at least on the guage)


Everyone jumps to the thermostat because its a good place to start. If, when the engine is truly at op temp, the upper and lower radiator hoses are both hot, its not the thermostat. If you have the temp control to hot and both heater core hoses are hot, its not the valve or control. Check the blend door actuator (behind the glove box), and then the blend door itself as it may be broken (its plastic) and not closing off the cold air.

Nov 07, 2009 | 1996 Ford F250 Crew Cab

2 Answers

Heat does not work. coolant level ok and temp is ok


Might try checking the temp blend door operation or the temp blend door actuator. If all good there perhaps the control head itself is faulty.

Oct 08, 2009 | 2000 Jeep Grand Cherokee

1 Answer

2001 Aurora - blows only 'warm' air


Your problem is either a clogged heater core, or the air temp control blend door actuator, in order to check for a clogged core feel the heater core hoses in the eng compartment, they should both be hot, one a little hotter than the other, if they are the core is ok and the blend door actuator needs to be replaced.

Dec 28, 2008 | 1997 Oldsmobile Aurora

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