We live in Central Florida and have a 3 ton Carrier Heat Pump which we
had installed by a local dealer in 1998. While it does manage to heat
or cool our home fairly well over all, I do have the following 2
questions regarding its' performance:
1) Many times per day while it is set for cooling, the air handler
will start and run for 5 or 10 minutes blowing warm air before the
compressor finally starts and the unit begins to cool.
2) Many times the compressor will start and run very briefly (approx.
1 or 2 minutes) and then shut down.
Although the dealer's servicemen have told me that this is "normal", I
remain somewhat skeptical about both items. It is not obvious to me
why either of these 2 conditions should exist. Can anyone offer some
insight into whether or not this is "normal" performance, and, if so,
what the reason might have been for Carrier to design it this way?
Thanks for any info and/or comments.
Replace deadspam with yahoo to reply.
This behavior sounds strange, but here are the two conditions under
which it MIGHT be "normal".
1) If your system is equipped with a "fan cycling" option (usually a
programmable thermostat feature) then it can be programmed to mix the
home's air several times per hour. However, you'd think that the dealer
would explain this feature to you rather than just saying it is
"normal". On the other hand if you hear the compressor trying to start
(but it doesn't) while the air handler fan is running then this is NOT
What is the brand and model number of the thermostat?
2) If the compressor is short cycling (running for a minute or two and
then shutting down, waiting for five minutes or so and then restarting)
while the temperature is being maintained at the thermostat setpoint,
then I'd suspect that the unit is oversized for your application, and/or
that the thermostat 'dead band' is set to 1 degree or less.
That COULD be a built in delay on the thermostat, AND outdoor unit working
together. 5 minute delay on each, IF the thermostat gets a call for cooling
within a set time frame after it ends a call for cool, the delay kicks in,
waits 5 minutes, sends signal to the outdoor unit, and it will wait 5
minutes no matter what for a start to cool.
IF the units oversized, thats called short cycle, and not good...OR,
forwhatever reason, your thermostat dead band is too tight, and needs to be
set a tad higher.
If its a digital stat, that is easy enough.
Wait till you experence the normal Carrier/ICP evap coil leakage..:), its
free when you buy a Carrier, Bryant, Payne or Tempstar unit.
And yes, what you describe, is indeed normal....depending on the setup,
stat, unit, and conditions.
Is it your opinion that it could be "normal" for the air handler fan
to often run for 5 minutes or more (blowing warm air) while waiting
for the compressor to get a signal to start?
I doubt very much that the system is oversized for our home. On the
other hand, the thermostat dead band might very well be set too tight.
It is a Carrier digital thermostat, but I'm not at all sure that
changing the dead band setting will be easy (or even possible) As I
mentioned in a previous post, the Carrier documentation explains how
to set the "Anticipator" to "control the sensitivity and cycle rate of
the thermostat. It allows settings of 1 through 9, and sounds simple
and ideal -- but unfortunately it has no effect whatsoever on
sensitivity and/or cycle rate. When I questioned this performance, the
dealer's serviceman told me that it "is only effective when the system
is set for "Emergency Heat". You probably can imagine how dumb that
sounds to me. Anyway, I thank you for your comments, and if you have
more I would appreciate hearing them too -- especially if you could
tell me how I can really change the sensitivity and cycle rate.
Not just normal, but built in as part of the package.
You state you have a digital stat, a Totalline unit. Its got a built in
delay and its called COMPRESSOR PROTECTION.
Every unit I install has this, and every stat I install that is digital, (I
use Honeywell ONLY) has a built in delay.
Then, you add the delay on the defrost control that the unit has, and you
have a delay...yes...its VERY normal, and every major brand has this.
The circumstance behind the delay is what matters. AT times, depending on
the on board timer, you will have a delay, or you wont have a delay. Its the
time between cycles that matters, and the length of time between the time
the air handler starts, and the outdoor unit kicks in may vary.
Depends. You dont know. I dont know. The ONLY way to know is to have a
complete Manual J calc ran.
No..actually I cant imagine. The heat anticipator, basically what the cycle
rate is, allows the unit to run and not overshoot the setting temp. On
mercury stats, this is an easy thing to do with a resistor. SOME digital
stats have a resistor that is located in a position to influence the
thermocouple that determines the air temp. Most use an algorithm to
determine the cycle rate.
Emergency heat on a heat pump will be either fossil fuel, or electric strip
resistance heat, and in both cases, an anticipator is a must..be it a
resistor, or electronic.
Change that thermostat to a Honeywell. :)
I dont like...matter of fact, hate, (hate being a strong word) Totalline
However, if the system is designed and installed properly (and not
oversized) I'd expect this confluence of events to happen rarely, not
"many times per hour".
The TSTATCCNHP01-A it has a three-minute Minimum On Time Timer. In
normal operation, when a stage turns on, it will not turn off for a
minimum of 3 minutes. I don't recall whether that time is measured from
the time that the thermostat calls for cooling or from the time that the
compressor timer expires. One would hope that it is from the time that
the compressor timer expires, but knowing Carrier....
Also, the 'stat has a four cycle / hour timer that is designed to
preclue your system from starting more than once every fifteen minutes.
This isn't consistent with your observation of 'many times per hour'.
I don't know either, but I sure hope your contractor did a Manual J heat
gain / loss calculation before they installed that puppy. Do they have
a copy of it? If not you can entertain yourself by doing your own. The
most accurate (free) personal-use calculator I've found is the old
Lennox application; now out of date but still accurate enough for your
purposes. Get out your measuring tape and download a copy from
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