Air Conditioning - Accumulator and core

I have a 4.5 ton Carrier central A/C unit that is about 7 years old but it works good. The dryer and accumulator are located outside of the compressor unit. The other day the unit had been on for a while and I noticed that there was a thin layer of frost all over the accumulator. Is this anything to be concerned with?

Secondly I was cleaning the evaporator core the other day and noticed that the outside edges where the piping comes out and bends around to go back the opposite direction had a lot of rust on them. The pipe was not rusted since it appears to be copper but the metal that supports the pipe was rusted. I believe the evaporator core is 14 years old. I would assume this could be a problem real soon. Comments?

Thanks

What was the load on the system when you saw the ice ?? Was it cool outside ?? Normally you don't want to see any ice or frost but low load conditions could cause it.

The rust on the metal on your coil is normal for the age and at 14 years old your approaching the last end of its life. 15 - 20 years is average life on a straight a/c 10 - 15 on a heat pump.

I'm guessing the unit had been running for about 30 minutes and the outside temperature was around 80-85.

Thanks for such a quick reply.

Good chance you are getting low on freon. As long as you have good airflow across the evaporator coils you should never see frost on any of your pipes for longer than a few minutes.