An up flow air conditioning evaporator coil is typically found on top of a gas furnace. Your coil may be housed in it's own metal cabinet called a Cased Coil or you may have a coil set inside of a metal or fiberboard supply plenum. To find the coil you will need to remove the cabinet screws if it is a cased coil or you may have to cut into the plenum with sheet metal cutters in some cases. Please be fore warned that if cutting into a sheet metal plenum extreme care must be used so as NOT to cut into any refrigerant copper lines as there is usually extremely high freon pressures in these lines.

Checking for freon leaks involves being sure there is some freon in the system or you will have no pressure to complete the check. This is done by painting a strong non alkaline solution made for this purpose (don't use household products as they are corrosive eventually) on any and all joints of copper, fittings, capillary tubes, tubing bends, metering devices or T.X.V. (Thermal Expansion Valve), strainers, filters, dryers or any other connections. The refrigerant lines that run from the evaporator coil to the outdoor unit are checked in the same manner. Be sure to check the small capillary tubes that are protected with a black piece of refrigerant line set insulation. Vibration over the years often make leaks at these tubes - if they are leaking a VERY skilled service technician MAY be able to seal the leak but usually it is time for a new coil. All the tube bends at BOTH ends of the coil need to be checked (if you can get to them). The metering device or TXV also need to be "checked". If using the leak solution, paint it on liberally and watch VERY closely for any bubbles no matter how small they may seem. Any bubble is a leak and needs to be repaired.

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Finding Freon Leaks
If you are going to attempt this always wear protective eye wear and gloves as freon in the eye will burn the eye PERMANENTLY! Many have the misconception that freon freezes. The exact opposite is true. If you let freon out on the ground (an E.P.A. violation) it would boil even at a temperature of about 40 degrees below zero! If unsure of yourself, please call a qualified HVAC Company to do this work.
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