It’s not failed yet, but the inside coil is starting to have frost on it, so I’am thinking it has a leak somewhere. I don’t have the money for a whole new unit. So i was going to purchase a coil myself and I’am a tech install it. What’s your thoughts?
Newer units have higher SEER ratings. It will affect how the system performs if it’s not matched to your condenser. More of a problem if it’s a heat pump, but it looks like your unit is AC only so manageable, but you may lose your ability to remove humidity.
A frosted coil can be the sign of many different issues, refrigerant loss is only one of many possibilities.
Check your air flow (clean filter, blowers belt in good shape, blower wheel clean, floor registers all open, return air not blocked, evaporator coil clean on BOTH sides, blower motor capacitor providing proper capacitance, etc..)
What outside temperature do you run your AC at? If it’s too cold outside then it could be dripping down your head pressure too much causing the iced coil.
Filter dryer blocked up or restriction at the metering device can cause it also. Where exactly is the frost starting to form?
20 years is an old system but my concern is replacing the evaporator may not fix the issue, or the leak if it’s leaking at the condenser or somewhere in between. It may be cheaper to fix the issue than throw a dart at the evap coil.
It’s true what they say. They don’t build it like they used to. Everybody now wants high efficiency but they don’t realize that more often than not those systems have shorter lifespans and higher maintenance/repair costs. The overall savings in my opinion is debatable.