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Cooling · RepairEvaporator Coil Replacement
Evaporator coil replacement means recovering the refrigerant, cutting the leaking indoor coil out of the plenum above the furnace and brazing in a new one matched to the outdoor unit, usually most of a working day. Replace the coil alone when the system runs on R-410A and is under about ten years old. Price a full system instead when it runs on R-22 or is past twelve years.
An evaporator coil fails by leaking, and three mechanisms account for nearly all of it. Formicary corrosion is the common one: formic and acetic acids, formed from household vapours such as cleaners, adhesives and new flooring, eat microscopic branching tunnels through the copper tube wall until refrigerant seeps out at dozens of pinholes. The second is vibration, which cracks the brazed U-bends at the ends of the coil. The third is not a refrigerant leak at all: the steel drain pan under an older coil rusts through and drips water onto the furnace.
The leak has to be proven to be in the coil before anyone sells you one. We use an electronic detector at the coil face and end plates and, where the reading is marginal, isolate the coil and hold it under nitrogen pressure. A low charge with a tight coil means the leak is at a flare, a service valve or the outdoor unit, which is a different and usually cheaper job covered under AC refrigerant leak repair.
The replacement coil must match four things: the tonnage of the outdoor unit, the refrigerant, the metering device and the cabinet it sits in. Furnace cabinets come in standard widths of 14.5, 17.5, 21 and 24.5 inches, and a coil wider or narrower than the furnace needs a sheet-metal transition, while the plenum above is cut back or rebuilt to the new coil's height. A cased coil arrives in its own insulated cabinet and stacks on the furnace like another section; an uncased coil is a bare A-frame slid into the existing plenum, cheaper but only as good as that plenum's seal. The metering device, a piston or a thermostatic expansion valve, has to be the one the condenser manufacturer lists, because a mismatch floods or starves the compressor.
Coil only or full system depends on the refrigerant and the age. An air conditioner on R-22 was almost certainly built before 2010, and R-22 has not been produced or imported in Canada since 2020, so a new coil would be filled with reclaimed refrigerant and bolted to a condenser at least 16 years old. New equipment moved from R-410A to R-454B and R-32 in 2025, but R-410A coils and refrigerant are still supplied for servicing, so a 2016 system is worth a coil. For other cooling faults see AC repair, or ask for both prices in writing.
Signs the evaporator coil is leaking
- Cooling fades over a few weeks and a refrigerant top-up buys only part of a season
- Ice on the indoor coil or the large copper line with a clean filter and open vents
- Oily residue on the coil end plates or U-bends
- Water or rust streaks on top of the furnace from a rusted-through drain pan
- A leak detector that alarms at the coil while every outdoor joint tests tight
How it works
Electronic leak detection at the coil, then a nitrogen pressure test if the reading is marginal. A coil is never condemned on a low gauge reading alone, and we look up the serial number for remaining parts warranty before quoting.
An ODP-carded technician recovers the charge, opens the plenum, removes the old coil and sets the replacement level so its pan drains. Joints are brazed with nitrogen flowing through the tubing to keep scale out of the system, and a new filter-drier goes into the liquid line.
The circuit holds nitrogen pressure, is pulled into a deep vacuum and is charged by weight, then checked by superheat or subcooling and by the temperature drop across the new coil. The plenum is resealed and the drain is tested with water before we leave.
Brands: We replace evaporator coils on Lennox, Carrier, Trane, Goodman, Rheem, York, Amana, KeepRite and Daikin systems, using the coil the manufacturer lists as a match for your condenser.
Common questions
Can a leaking evaporator coil be repaired instead of replaced?
A single cracked U-bend or a rubbed-through tube can sometimes be brazed, and we will say so when that is what we find. Formicary corrosion cannot: the pinholes are spread through the tube walls, and sealing one leaves the next to open before long. Leak-stop additives are a gamble, because they can foul the metering device and the compressor.
Is my coil still under warranty?
Possibly. Most manufacturers give a registered system ten years of parts coverage and an unregistered one five, so a seven-year-old coil may be covered for the part while you pay labour and refrigerant. The replacement coil has its own registration deadline, commonly 60 to 90 days from installation. Check the card that comes with it, and keep the invoice showing model and serial numbers.
Can I keep my R-22 outdoor unit and replace only the coil?
Technically yes, practically rarely. The new coil needs a metering device suited to R-22 and a full charge of reclaimed refrigerant, which is the costly part, and the condenser it serves is near the end of its life. That money buys a new coil on an old compressor. R-22 air conditioner repair sets out the options.
Does the furnace have to come out to replace the coil?
No. The coil sits in the supply plenum on top of an upflow furnace, and the work is done by opening that plenum. In the tight basement mechanical rooms of 1970s–90s subdivisions, a gas vent, a humidifier or a low bulkhead can be in the way and add sheet-metal time. If the furnace is also past 15 years, replacing both together avoids paying for the plenum work twice.
Is it safe to run the AC with a leaking coil?
It is hard on the equipment. A low charge drops the coil below freezing, the coil ices over, and liquid refrigerant can reach the compressor, the one part you cannot afford to lose. Turn cooling off, run the fan to thaw the ice and book the leak test. Is a refrigerant leak dangerous covers the health side.