When I run my ac it makes a clicking sound under the dash

That is not a relay in my opinion it is the gear drive AC/Heater temperature control blend door actuator, the gears are jumping over each others teeth and that makes a clicking sound. This is caused by a binding air temperature control door inside the dash near the speaker.

OK, usually when you turn your AC on the clicking sound should be the compressor turning on.
Just to verify, open the hood, and have somebody else turning on the AC, you will hear a clicking sound. From here you should know if it's the same sound.

HI THE CLICKING SOUND IS PROBABLY A HEATER/AC ACTUATOR WITH A STRIPPED GEAR , WHEN THIS HAPPENS TRY TO MOVE THE HEATER CONTROL KNOB FOR THE MODES (DEFROST/FLOOR/VENTS) SEE IF NOISE CHANGES . IF IT DOSE THEN THE ISSUE IS WITH A ACTUATOR UNDER THE DASH

You have a defective heater/AC temperature control motor likely due to a warped diversion door.

There are many possibilities that can cause car to make noise.

It's actually from where the noise is coming from. Front end or rear end. From engine area or from inside the steering or from brakes.

There is N-number of possibilities for the car to make grinding noise or any other kind of noise.

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For step by step troubleshooting this problem, I suggest you to refer the help links mentioned below. Its a complete solution with proper explanation to identify the cause of problem: ------

Click the link below: -----

ABS light comes on and Car makes Grinding noise?

http://repairhelpcenter.blogspot.com/2012/01/abs-light-comes-on-and-car-makes.html

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Car makes clicking noise?

http://howtobyme.blogspot.com/2011/11/car-makes-clicking-noise.html

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Car makes whining noise like driving on rough pavement?

http://howtobyme.blogspot.com/2011/12/car-makes-whining-noise-like-driving-on.html

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Chirping Noise From Car?

http://technoanswers.blogspot.com/2011/11/chirping-noise-from-car.html

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What are the possibilities for Clicking noise in car?

http://technoanswers.blogspot.com/2011/11/what-are-possibilities-for-clicking.html

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Squealing at start up on car?

http://technoanswers.blogspot.com/2012/01/squealing-at-start-up-on-car.html

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Chirping sound coming from engine?

http://technoanswers.blogspot.in/2012/01/chirping-sound-coming-from-engine.html

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Vehicle making Clunk Thump Thud noise?

http://howtobyme.blogspot.in/2012/03/vehicle-making-clunk-thump-thud-noise.html

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4X4 Truck makes roaring noise in the front end?

http://schematicsdiagram.blogspot.com/2012/01/4x4-truck-makes-roaring-noise-in-front.html

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Heater makes clicking noise under dash on Ford Explorer?

http://technoanswers.blogspot.in/2012/01/heater-makes-clicking-noise-under-dash.html

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Clicking noise under dash and front defroster not working?

http://technoanswers.blogspot.com/2012/01/clicking-noise-under-dash-and-front.html

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Car Brakes Making Noise?

http://repairhelpcenter.blogspot.com/2011/12/car-brakes-making-noise.html

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Car Alternator making noise?

http://repairhelpcenter.blogspot.com/2011/11/car-alternator-making-noise.html

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Car Alternator Bearing Makes Grinding noise?

http://repairhelpcenter.blogspot.com/2011/12/car-alternator-bearing-makes-grinding.html

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Engine makes noise and Cooling Fan belt Breaks?

http://howtobyme.blogspot.com/2011/12/engine-makes-noise-and-cooling-fan-belt.html

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Vehicle Makes Clicking Sound While Taking turns?

http://schematicsdiagram.blogspot.com/2011/12/vehicle-makes-clicking-sound-while.html

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These will help.

Thanks.

Your ac blend door is broken or the actuator that opens and closes the door is broken. The ac blend door moves up and down to direct air flow through the heater core(for heating) or evaporator core(for cooling).

When the door mechanism breaks, the blend door falls down and you will only have ac but no heating.

You can buy a ac blend door kit for your explorer, they cost about $120 on ebay or other places.
search for Explorer ac blend door kit.

The duct is under the the dash on the drivers side. And you will have to cut open the duct to install the replacement door.

Heres a link to a tutorial of how to do the job.

http://www.heatertreater.net/Ford%20Explorer%2002-08.html

where do you park your car. Is it under trees or garaged. You may have leaves **** in it. go under your dash and take it down and check. Most are pretty easy to get to.

We have heard that complaint before, and it was the ac clutch cycling under the hood. It does sound like it is coming from the dash. The next time it is making the noise, open the hood and inspect the front of the compressor. It may be stopping and starting. The only other cause could be a mode actuator for the ac/heating system. Your vehicle has electric motors that move the air to defrost, floor, inside or out, etc. One of those actuators could be malfunctioning, but they usually just stop working. I would check the compressor first. It may just need additional freon. Hope this helps

If this noise is a clicking sound and is coming from the front center of the dash, then it may be the blender door motor which will require removal of the dash to replace it. It will keep the door from switching from heat to a/c. Does the odor smell like you have a freon leak in your a/c evaporator core or does it smell like a rat stuck in your heater and a/c ducts?

sorry never had one apart sao i cant finger anything in particular,remove any coversa and put head under and have a look,could be a faulty climatic computer or just a rubber pipe come off eoither on teh inlet manifold or on a flap operating mechanism