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I just bought this unit used and noticed the a-coil is bigger than the top of my furnace. Do I need to get another a-coil or build a bigger plenum for my furnace.

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If it is less than 4" you can split the difference on each side. as long as it is sealed properly the slight restriction at the coil wiil want hurtr much. As stated make sure to seal it so all the air goes though the coil.

Posted on Aug 21, 2010

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You should prob take the coil back an get the correct size for your furnance .you can build plenum if you like lotta extra work though

Posted on Aug 21, 2010


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Why can't I get air flow into rooms?

The problem may be at the plenum. If the ductwork is connected at the very top of the plenum it can't build up STATIC PRESSURE. If the plenum was on the floor in front of you, you would measure down 12-18", from top to bottom, and that's is where the ductwork should start on the plenum. It may be hard to understand but we are not supposed to connect any ductwork on the HEAD of the plenum, as well as 12-18" from the top. If your blower is forcing air pressure from the bottom, into the plenum, and we release that pressure by cutting openings in the top, the pressure does not build inside the plenum. but with the ductwork away from the top of the plenum, air is forced in from the bottom and pressure builds at the top allowing a higher STATIC PRESSURE inside the plenum. And that pressure is released into the ductwork at a higher velocity and more evenly per duct. Most installers don't know about static pressure and will attatch ducts at the top of the plenums box. The blower then has a lower pressure and, although you feel some air in the problem room, its not enough volume to condition the whole area. That's a tough fix by the way but if that's your issue, have it replaced and if done properly you will notice a difference. An 8" flex duct is around 220-240 cfm. Depending on your size of room it may be a large enough duct. Normal size bedroom(not master) is about a 7" with non-foam insulation. An 8" is common for a kitchen due to the heat load so your 8" to that room should be blowing good. You may also try to increase the blower speed, make sure your evaporator coil is clean, and at the plenum there should be dampers that you can control the air flow per duct. I've seen that %75 of the time, with poor air flow its the placement of the dunt at plenum. Hope this helps!

Jun 28, 2015 | Heating & Cooling


You can add Air Conditioning to Your Hot Air Furnace

Air Conditioning is easier to add to an existing central hot air heating system then you might think. Both systems use air to move the heating or cooling to the different parts of the house. With the addition of a coil and condenser to your system you can stay nice and cool all summer long.

The easiest way to add in cooling to a system is to install a coil on top of the furnace supply air plenum. This can be accomplished by cutting open the supply duct just on top of the furnace and sliding the air conditioning coil right in on the top of the furnace. The only limitation usually is the height of the plenum. If there is not enough height there, then the coil may need to be installed on a horizontal run.

If the horizontal run option is needed then you will have to make sure that all of the air flow goes through the run. If all of the air does not go through that run, then the ones that do not go through will not cool nearly as effectively as the rest of the runs that go through the coil.

After placing the coil in the ductwork, the piping and electric will need to be run to the outdoor condenser unit. After wiring and piping the unit the refrigeration lines will need to be purged, and vacuumed. This will clean the lines and take the air out of them. Any air in the system will cause the system not to work properly.

When all of this work is done you will be ready to have great cooling. The whole process usually takes me less than a day to complete. Adding cooling to an existing system is a simple operation when it is done by someone that has done it many times. If you have a hot air central heating system without the benefit of cooling, then you should check into adding the cooling feature to your system. You will be glad you did when the hot weather rolls back around again.

on Dec 08, 2009 | Heating & Cooling

1 Answer

How do i clean coils inside intertherm unit

Do you mean the inside coil? If so the plenum on the furnace will need to be opened and sprayed with a coil cleaner, preferably one that foams. If you have pets you might need to take the cover on the end of the coil off and take a vacuum cleaner or shop vac and clean the hairs off the coil. You don't need to rinse as it will clean its self when running.

May 11, 2014 | Intertherm Heating & Cooling

1 Answer

Getting excessive condensation causing water problems at base of unit. Bought new pump but problem returned. Cleaned lines to outside by using wet/dry vac. How do I get to evaporator coil to spray it and...

Hello, in order to get to the evaporator coil you must cut into the plenum above the Furnace. This will require sheet metal tools and being very careful not to puncture the coil. Many times a cracked condensate pan under the evapoartor coil can cause water to leak down to the base of the unit.

Sep 15, 2011 | Ruud UBHC Air Conditioner

1 Answer

Where is the filter in the Weatherking furnace that is in my home that I bought?

The big square grill inside the house is the return air plenum (box). That is how the air gets back to the unit to be heated or cooled. The filter is somewhere in the return air stream.It could be behind the square grill. It could also be where return air enters the furnace or behind a plate on the furnace near where the return air enters.Shine a light into the grill and you may see it. Look for a 1" wide box with a bigger perimeter than the plenum near the furnace. it will have a cover. Remove an access panel on the furnace near the return air.They usually come off very easy. Check the manufacturers web site they may have some manuals on line. good luck

Aug 10, 2010 | Weather King 12AJA4801AH Air Conditioner

1 Answer

Condensation in the furnace, as a result of which air is not being circulated. Air conditioner is Carrier Model#38CKC036340. Is there any place where I should be removing the condensed water??

The coil for the AC sits above the furnace. Two refrigerant lines enter the
plenum, usually the condensate line is on the same side and at the bottom of the plenum. Sometimes they use pvc pipe or a garden hose to drain the condensate.

Your problem is worse than that, it sounds like your indoor coil is froze up, that is why you dont have airflow, either you have a dirty filter or your fan does not work

Jul 08, 2010 | Heating & Cooling

2 Answers


The condenser coil is in the outdoor unit. Turn off the power. Take a garden hose without the nozzle. You want to use gentle pressure. Just simply using your thumb to control the spray. Spray the water up at an angle under the slanted lovers. use a generous amount of water. you should see the dirt coming our. You will have to take the cover off to clean that side of the coil. Be careful so you do not get the electrical controls wet when the door is off. The Evaporator coil is located in the supply air plenum downstream of the airflow. ( the top if its in a basement). You probably will need to open the ductwork.
Good luck.....

May 02, 2009 | Ruud UAKA042 Air Conditioner

1 Answer

Central air conditoner unit doesnt blow cool air into home has some ice on the inlet heat and cooling lines going into the central air unit

Change the furnace filter. Make sure you use a cheap one when air conditioning, as the better ones restrict airflow when they filter out so much stuff and then plug up, not allowing enough air to pass over the cooling coil in the furnace's air plenum. Turn the A/C off for a few hours (with only the furnace fan on if possible) to melt the ice off the cooling unit inside the furnace.

Sep 01, 2008 | Carrier Heating & Cooling

1 Answer

My central air unit keeps freezing up on the inside

1) locate the A-Coil (A-frame) inside the furnace. It is usually located in the furnace supply plenum located on the "down" side of the furnace plenum. If it is very dirty, there will be poor air flow generally in the house. This can cause the A/C to "freeze up" as the refrigerant is not getting enough heat to convert the refrigerant to a gaseous state.

2) The unit may be low on freon (or whatever refrigerant you are using). Contact a serviceman to check the unit.

Jul 07, 2008 | Coleman Heating & Cooling

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