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?
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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