I have a 7 year old 3 ton Trane XR12 heat pump unit (2-stage heat, 1 cool)
servicing a 1500 sq ft single story house in North Texas. The outside
compressor is located in a western alley where it gets direct sun about
2:00 pm for a couple hours but is otherwise shaded by my/my neighbors
I like my AC cold, and have run this unit at 70 F for the past 7 years
without a hitch. The one air filter is changed monthly, anf the outside
coils are clean. Sight glass shows everything clear. The unit has performed
flawlessly, like a champ.
Recently, though, corresponding with some record high temperatures
beginning about the time the sun hits the outside unit/and/or the outside
temp hits 101-102 the unit stops produding cold air. Up until that point,
works perfectly, hits set point 70 with no problem. Just updated thermostat
to Honeywell 7-day, same behavior, that is, later in the evening, about
8:pm or so, when the outside temp drops down below 100, the cold air starts
up again and the house cools down as set on the thermostat. Ice cold, so
freon seems good. Rinse and repeat with each 102-3+ F day so far.
Is the unit, which outside of these extremes seems to work flawlessly/no
differently than last 7 years, protecting itself somehow with some type of
automatic limiting switch? Or is this indicative of some breakdown that
would require technician service?
Thanks for any insights. In the meantime, I'm warm now, I'll be cool
tonight and tomorrow morning, and mid afternoon forward tomorrow I'll be
warm again, unless something changes.
The unit does not 'blow air of a certain temperature', it
blows air of 20 - 25 degrees colder than the air going into it.
It does so with a certain amount of air, perhaps 1200 CFM for
this unit. Do the math and that's the amount of heat load it can
handle, IOW heat it can take out ( not accounting for himidity here ).
If the total heat coming in is more than that, the building
will warm up.
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Thanks, Paul. That was my initial theory, too. But when I set a thermometer
in a bathroom register, it read a constant 80 degrees - until the
compressior finally kicked back on and the temp then started falling
rapidly, so rapidly that I could see it drop.
One time that happened after resetting the thermostat, the other after
installing the new thermostat when I had cut the breaker off. That's when I
began to suspect some type of switch that cut the compressor or condenser
or whatever out of the system entirely. Since when it reengaged it
proceeded to work like a champ, once again pushing the house temp back down
to 70 overnight, I assumed I didn't have a freon problem.
What I guess I don't understand is the rapid, measurable cooling after
resetting the thermostat. If what you're talking about is all that's going
on, I'd expect to see very gradual warming all day, not the case, followed
by just as gradual and imperceptibly measurable cooling.
But obviously I don't know enough about how an AC/heat pump unit like this
Trane XR12 differes from a straight AC, and none of my user manuals talk
about any protective switches or cutoffs or anything.
Thanks again for the help.
PM...preventative maintenance? No, only by me, keeping the drain line clear
down through the trap it empties into, keeping the outside unit clean, but
it doesn't really accumulate anything but a little dust, no leaves, etc. No
freezups, sight glass always clear, no bubbles, no colors.
Possible - compressor overheating
Possible - high limit switch on compressor tripping ( this is very
often a manual reset, but not always ).
Try - cutting power to the condensor and restoring it IOW flip the
breaker. If that restores cooling immediately, it's one of the above.
Disclaimer - there may be a minimum cycle time at the condensor.
Time for some gauges and a good servce tech.
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First off, replacing the thermostat is like saying "my car isn't working
right, maybe if I replace the ignition key...
Thermostat is nothing more than a temperature controlled ON/OFF switch.
I am curious as to the design temps there.... Correctly sized systems will
not keep up in record heat. If the design temps are 75F with 50%RH inside,
at 98F outside, when it hits 98F outside, it will be running continuous to
maintain that 75F inside. if the outside temp is higher than that, the
inside temp will rise commenserate. If your able to maintain 70F @ 102F
outsied, I would be willing to bet that the system is grossly oversized.
This is not a good thing either.
COLD air is not good, it should be cool and dry. You need to call a
competent tech to check and service the system. IF its low on refrigerant
(FREON), the first thing the tech should do is find out where it went.
Refrigerant is not "consumed". If its low, there is a leak.
Thanks, Steve. While this may be true, I nevertheless felt I had the
personal freedom and budget to upgrade my 7 year old TayStat 540 to a
Honeywell 7 day unit in order to begin controlling my usage more finely
than I had done in the past, since I will be changing electricity providers
next month as well.
Since I am not able to maintain 70F @ 102F and never claimed I was, this is
not a problem. The unit is a 3 ton Trane XR12 Weathertron heat pump matched
to a 3 ton air handler. The unit it replace was a 2.5 ton outside unit
matched to a 3 ton air handler. My house is one story, 1500 square feet.
I enjoy my air cool and dry at 70 degrees F, although as electricity costs
keep rising I may find myself raising the temperature of the cool and dry
air I enjoy accordingly.
While all above maybe correct and according to you, condenser maybe
clean you must take in account corrosion which can cause condenser be
coming inefficient and does not transmit/pick/discharge heat as it has being at
that temperatures afternoon compressor gets overheated results in shut down
which you perhaps did not notice. Also once compressor shuts down at high
temp it may take an hour or longer before it cools down to come back on.
Remedy buy new unit with little more capacity "OR"
put sprinkler on it after noon's. Sorry that is life!!!
Thanks, guys. So, one, two, three...five respondents, and none of you is
directly familiar with a 13 SEER Trane heat pump? Does Turtle still come
around these parts? Or maybe they just sell more of these odd Trane systems
around where I live than elsewhere for some reason.
Except for this novel anomaly during a string of record heat days we
haven't seen since 1980 I've just started having (I'm home all day), since
my system continues to function perfectly otherwise, I was trying to
determine if the anomaly was a normal function or not, since A/C calls are
currently running at a premium around here. I had called my guy who put the
unit in the first and second years after installation and he told me that,
unless there was noticeable debris or dirt in the outside unit, there was
really no worthwhile maintenance he could perform on a unit so new. Since
then, whaddya know, it's been 7 years now.
Christopher, the cleaner you're referring to would seem to be this Virginia
stuff sold by Grainger:
but now I'm thinking that, rather than spring for 20 bucks plus and do it
myself, I'll just put that $20 toward a full maintenance call, even if this
episodic condenser/compressor cutting out phenomenon is normal for these
Trane units in our current record outdoor heat.
Thanks again for all your responses. If anyone does know authoritatively
about protective Trane switches and how they operate, though, I'd still
like to know.
It most likely does have high and low pressure safetys in it... if its
tripping in high ambient heat, its most probably tripping on high pressure.
The tech needs to find out why and correct the problem. FWIW, most problems
either show up during extreme heat or extreme cold. More often as not, its
due to lack of being serviced, and/or it wasn't serviced correctly the last
time, and/or improper installation.
Another thought.... keeping the thermostat @ 75F for cooling instead of 70F
will most likely drop your energy bill as much as 30%.
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