In May of this year I posted a message to this ng with the subject
"Heat Pump Performance Questions" where I listed what seemed to me to
be erratic control circuit performance of a Carrier Heat Pump system
in a cooling mode. (Many times per day the air handler would start and
run for 5 to 15 minutes before the compressor started). When the
compressor did start the system seemed to operate normally, and the
cooling was good. Some of the responses to this post pointed out that
all HP systems probably include timing circuits meant to protect the
compressor. For example the literature that came with our Carrier
system refers to (1) a five minute Compressor Timeguard which will
prevent the compressor from starting unless it has been off for at
least 5 minutes, and (2) a Fifteen-minute Cycle Timer which prevents
the start of a heating or cooling cycle until at least 15 minutes
after the last start of the same cycle. It also refers to a Two-minute
Minimum On Time, where a stage once turned on will not turn off for a
minimum of two minutes.
These all sound like reasonable protective features to me, but I don't
think they explain the performance I was seeing. At the time of my
first post on this subject in May of this year our system was
performing erratically (in my opinion) many times per day, with long
delays before compressor startup and unexpected compressor shutdowns.
None of these delays or shutdowns seemed to me to be connected to the
above-described compressor protections. Then as our weather got
hotter, and in fact throughout the entire summer (here in central
Florida) the system performed very normally and the compressor delays
and shutdowns seemed to vanish. But now that the weather has
moderated, all of the problems apparently have returned. Even after
the the system has been off for 30 minutes or more, a call for cooling
by the thermostat often results in 5 to 15 minutes of air handler
operation before the compressor starts. At other times both might
start together but the compressor might stop after a few minutes (and
remain off for 5 or 10 miinutes) while the air handler continues to
run. Then the compressor will start and normal cooling will resume.
The compressor and/or the outside fan seem to have minds of their own
-- running when and if they feel like it. (I have attached ribbons so
that I can easily see from inside the house if the outside fan is
running -- but I can't always be sure about the compressor itself.)
The service manager for the installing dealer has finally admitted to
me that this operation might be faulty (after long contending that the
performance was "normal"). He says that there are two control circuit
boards which might be causing the problems. He now suggests that I
have them replace the two boards (which are under a 10 year parts
warranty) at a cost to me of $90 labor for each board, plus a $69.95
service call charge -- total cost to me of $249.95 -- to see if this
will fix the problem. At the same time he suggested that they set the
new boards with no delays "so that everything starts at the same
time". I'm not ecstatic about the quoted cost for a "try it and see if
it helps" fix -- and his suggestion to eliminate the delays makes me a
bit uncomfortable too. (If this is an acceptable tactic, then why did
the original design include the delays?)
I hope to discuss this further with this service manager, and
hopefully also with one or two other "experts" (if I can find one or
two). I'm also wondering if it might be worthwhile for me to try a new
thermostat (Honeywell this time to replace the original "Carrier"
stat) to see if that might fix the problems.
As you can probably imagine -- any helpful suggestions will be greatly
appreciated. For example, could these problems possibly be linked to a
faulty thermostat? Would trying a new t-stat be a good first step?
Sorry this post is so long -- but I thank you for wading through it
and for offering any suggestions.
Replace deadspam with yahoo to reply.