Subject: Re: Heat pump

From: Doug Geddes <[email-masked]>
Date: 07 Oct 1995 02:27:00 GMT

>In article <[email-masked]>, [email-masked] (Peter Robson)
>writes:
>
>>
>>Hoping that this is the right group to contact, I have a problem,
>>relating to a heatpump, that needs solving.
>>
>>The electric fan motor on my house furnace recently seized  and
>>whether it contributed to or there was  just a coincidence, parts of
>>the A-type evaporator coil in the plenum of the furnace and connecting
>>pipework leading to it began to freeze.
>>
>>The electric motor has now been replaced with a new one and the
>>freezing has just begun again.
>>
>>The ambient rise in temperature then and now is something that I've
>>noticed which may have caused the airconditioning to react.
>>
>>What should I be checking out to correct this problem?  What else do
>>you need to know to help me correct my predicament?
>>
>>
>
>You have, indeed, found the right group. Failure of the indoor fan motor
>(insufficient airflow across the coil) will definitely cause the coil to
>freeze. With the fan motor replaced, the coil should not be freezing.
>Possibly the new motor is set on the wrong HP (fan speed). Check the
>temperature of the air entering the furnace (return air) and the
>temperature of the air leaving the furnace (supply air). The difference
>between these two temperatures should be no more than 20F for standard
>efficiency and no more than 26F for high efficiency systems. Exceeding
>these numbers indicates insufficient airflow and may cause the coil to
>freeze.
>
Hope this he>lps,
>Gary

Good advice Gary.  I would like to add a little more in case the motor is 
wired for itd highest speed.  The new motor may be less powerful than the one 
originally in the furnace.  It may be rated at less horse power - 1/4 vs 1/3 
for example, or it may be less efficient.  That is, it may use the same amount 
of energy but produce less blower speed.  Another potential problem is a 
blockage in your duct system.  Has a return air inlet been obstructed, have 
dampers been accidently closed (possible by duct cleaners), has sound 
insulation fallen off the duct into the air stream, are too many floor 
registers closed or blocked, is the air conditioning coil clogged with dust ( 
a reas possibility if you do not have an electronic air cleaner or a special 
high efficiency filter, and most importantly, is the filter clean.

Hope this all helps.

Doug