My 2 ton heat pump outside unit (4yrs) was today making an unusual, low pitched grinding sound. The fan was still turning, air was flowing. But the inside furnace/ac unit (3yrs) was hot. The housing and pipes that do not usually get hot had gotten very hot to the touch. I turned it off and left it rest for 45 minutes. I cleaned the filter which was filthy. Fired it back up and it has been fine all day. Can anyone tell me if the dirty clogged filter was causing the sound/heat problem? Should I be worried about this? Fire away.
If it's a scroll compressor, they will pump some liquid refrigerant. If it isn't, then you might have done damage to the compressor. A dirty air filter can do a lot of damage. If your filter was that dirty, chances are that a lot of dirt was bypassing it. Call someone to check and clean the unit. Be sure to tell them about the dirty filter.
A dirty filter produces excessive resistance to airflow, and thus a drop in airflow over the indoor coil. In heat pump mode this is the hot coil, and it is under high pressure normally. With reduced airflow the pressure can rise well above normal, to levels that can be damaging to the compressor for more than one reason. Not to mention the fact that running it under this condition can drop the average economic efficiency (SCOP) of your heat pump to that of straight strip heat, or even lower. The energy saved with a clean filter is so much greater than the price of even a pricey filter, that you are losing a substantial amount of money by not replacing it regularly. I know that this might seem counterintuitive, i.e. spending more money on filters saves money, but there you have it. Once per month whether it needs it or not. You probably have a plugged up indoor coil now as well. Having it pulled and cleaned could easily pay for itself in the first season of running. It may be clean, it may not, but if you can visually inspect the coil through the filter hole or return air grill then you probably should take a peek at it.
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