Question about 1999 Mercury Grand Marquis

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How do I confirm a blend door / actuator problem?

The thermostat is good, the upper radiator hose gets hot, the hoses into and out of the heater core are both hot. The AC blows cold air. I can select, defrost, vents, floor, etc and have air come out of those zones. The 30 amp fuse under the steering wheel tests OK. how can i confirm a blend door without taking off the dash? Is there a code, a manual override? Some site said pressing "off and floor" would tell me something but i don't see what.

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Blend door concerns heat and cold air ducting flapper. whether electronic or manual truning of a knob there is a movement noise. a motor/s make/s a sound on electronic controlled ones or a turn knob harder at times to turn does this. then feel the changes hot/cold breeze and no breeze etc..on the vent according to what you turn the system on to do. it is best to confirm movement /motion of the internal motor or flapper during night time or early morning in the garage inside the car devoid of noise to hear the motor or flapping movement, must hear some motor effort or feel hand effort if cable to the heater valve is intact/ not snapped to open heater valves on the engine side. then inspect heater cable if heater is not working etc..hope this helps.

Posted on Nov 24, 2014

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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

2 Answers

No heat or very little heat in a 2001 blazer and iv tried everything ...it will blow some heat then go cold


Bad coolant flow. check for low coolant, also a thermostat could be restricting proper coolant flow. If coolant is full in the radiator than touch your upper radiator hose to see if it is hot. If their is proper coolant level and engine is warmed up to temp and radiator hose is cold replace your thermostat.

Nov 02, 2014 | Cars & Trucks

1 Answer

No heat replaced heater core thermostat


So the blend door opens? Does the fan motor blow? Are both heater hoses hot? That would indicate the coolant is circulating through the core.

Dec 12, 2013 | Ford Windstar Cars & Trucks

2 Answers

1996 chrysler cirrus heater fans not blowing hot air to vents or defrost. Not sure of actuator or thermostat. Since i dont know where they are. 2.5L V6 - 4 cylinder.


I will assume that your engine is full of coolent, and does not overheat. Now if your car takes like forever to heat up, It will be that your thermostat is stuck open, but after a while, you would have heat in your car. If your engine coolent hoses get hot, but your heater hoses do not, remove the heater hoses where they connect to the engine. This is the first place dirt, grime, and corrossion build up, stopping the flow of hot coolent from going through your heater core. (heater hoses stopped up at engine/waterpump connection.) Your heater core may also be stopped up if there is alot of corrossion present.

The thermostat is located directly under where your upper radiator hose connects to the engine.

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thermostat is sticking open

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Heater doesn't get hot on 96 chevy truck. Blows good, just cold. Replaced thermostat, flushed radiator. Any ideas?


Air Temperature Control Blend Door Failure No Heat or no AC (dependes on where door sticks)

In all modern cars there is a tiny DC electric motor driven gear drive that moves a plastic door that blends heated and cooled air from the AC and the heater core, this is called (interestedly enough) the air temperature control blend door actuator. The motor that moves this door fails because the door starts sticking from warping, most common complaint is no heat but it can be no AC as well. To replace these parts (blend door and blend door actuator) you must remove the entire dash from the car. Always have this problem confirmed by a dealer or qualified repair shop as it is a very expensive repair.

Other causes of no heat in the cabin are engine thermostats that are stuck open (engine runs cold) or air bubbles in the cooling system.

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1 Answer

Radiator fluid is not heating up /all componennts are working


Do the two heater core supply hoses get hot where they go through the firewall to the heater core? If one is hot the other cool to the touch then you have a plugged heater core flush it out with a garden hose, if they are both hot then a part called the air temperature control blend door is not moving inside the air ducting due to it being warped and jammed and/or the actuator that moves it being defective, to replace the blend door and its actuator requires the dash be removed from the truck to access the air ducting that contains the blend door.

Feb 10, 2012 | 1998 Dodge Ram 1500 4WD

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

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