Hello. I'm looking for some advice on my system and coil cleaning. I have a carrier infinity system with coil model CD5AXA060024ABAA. When I bought the house two years ago, I noticed that the electronic air cleaner was switched off. The EAC prefilter was really dirty. I just removed the EAC elements and replaced with a 4" media filter because EACs are too much work in my opinion. Then I noticed the A-coil was freezing over. I tired to clean the coil and called a technician out for repair. He told me two things: (1) compressor was not original carrier and looked like it had been replaced; (2) the txv was an r-22 model and he replaced it with an r-410a model. He suspected that the compressor had probably been replaced due to the incorrect expansion valve. When he worked on the system to replace the txv (located just outside the evap coil enclosure), he couldn't get the all the refrigerant back into the condenser, so he had to add some (after replacing the valve of course). Presumably the refrigerant charge was correct at that time.
Last year, I replaced the filter media. AC was functioning normally. In the winter, I noticed that the furnace high limit trips (according to the service mode event history on the infinity thermostat) if the return closest to the unit is blocked (toy box tends to move in front of it).
This year, the evap coil is freezing again. I have this feeling that the underside of the coil is really dirty because the system could have been running for years without an effective filter. The blower wheel was/is dirty too (tried to clean that with vacuum two years ago). When I open the evap access panel, I don't have access to the end caps of the coil. In other words, I am looking at the fins on one side. My cleaning technique has consisted of spraying coil cleaner on the front and reaching over the top of the coil and spraying on the back as best I can.
Here are my questions. If I remove more of the duct/evap casing so I have access to the end cap, will I be able to remove the end cap to clean the underside of the a-coil? How else can this be done without pulling the coil? Is cleaning from the top side likely to be enough? I have an appt on wed. with another technician but would like to get some opinions on whether it would be worth pulling the coil to clean it. Thanks for reading!