My house has a Rheem heat pump, installed in 1991 Model
#RPND-042C, with "Heater Kit RXPJ," according to its
nameplate. Temperatures are about 35-40 degrees F this time
of year where I am.
Often in the morning the heat pump blows cold air for a
half-hour (or more?). I had an HVAC service tech out here a
week ago. He could not find anything wrong.
Does it simply take a while for the refrigerant to get to
suitable temperatures for evaporation/condensation operation
when in "heating" mode?
What symptoms might I observe that indicate the unit needs a
charge of refrigerant?
Also, I would like an operating manual, hopefully with a
layperson's troubleshooting guide. Although I am pretty
handy and I would prefer to do electrical side
troubleshooting myself. Anyone know where I can get such a
manual for this unit? I tried both the Rheem and Ruud sites;
Would you like fries with that?
Seriously, unless you do this stuff all day long, you WONT be able to
troubleshoot it. Lots of techs cant diagnose heat pumps properly. You
would need refrigerant gauges, digital thermometers, wet bulb readings
and the ability to understand superheat and/or subcooling readings
along with a good knowledge of a refrigeration circuit and airflow.
You might want to invest your time and money more wisely into finding
a good hvac company that can diagnose and repair your system
Ask friends, neighbors, relatives and groups you belong to who they
use. You could also look up the local Rheem distributor and ask one of
them who they would use if their system broke and needed repair.
The refrigerant does not need time to 'warm up'. It should be ready to go
in a couple of minunits or less.
When you say cool air, what is that in degrees ? Most heatpumps will feel
cool to the touch for the air comming out as it is usually cooler than your
Are you cutting the temperature down at night and back up in the morning ?
That could be the problem.
One symptom of low refrigerant is the cooling coil will freeze up. That is
the outside unit in winter and the inside unit in the cooling mode. It will
also do that sometime on its own in the winter, but the unit should go into
a 'defrost' mode to get rid of the ice.
I estimate about 62 degrees F or lower. That's where the
thermostat's built-in thermometer was sitting this morning,
after I raised the thermostat setting from 67 to about 75 F.
The outside temperature this morning was about 40 degrees F.
When it seems to be running correctly, the air coming out is
warm to my touch.
Yes. Typically we set the thermostat to 67 F for nighttime
sleeping. Then we raise it to 75 F or higher upon rising.
What's going on?
I do see the warnings on the net about playing with the
thermostat too much. I presume the control system for the
heat pump has trouble catching up to a lot of changes.
I will inspect the cooling coil sometime soon in the
Also, this morning I heard a pulsating noise coming from the
unit. Right now, with the ambient outside temperature at 59
degrees F, the heat pump is working fine, raising the
temperature from about 67 degrees F (setting while I was
running errands) to 71 F pronto. Nice warm air is coming
out. I hear no pulsating noise. I will inspect tomorrow and
see if it's the guts of the compressor making this noise or
what all. I am also of course open to suggestions.
J.A., I understand from reading that heat pumps differ from
furnaces in that the hot air they produce is not as hot as a
furnace set on high. But the things will get the house up to
the desired temperature, if all is in good working order.
Bubba, fair point. I work on my car a lot and consult the
Honda newsgroups for same, but one area that people tend to
stay away from advising DIYers on much is the air
I bear in mind that, from my reading, 16 years is very old
for a heat pump. I am keeping my eyes and ears peeled for
catastrophic failure of some parts.
Thanks for sharing your experiences, Bubba, Ralph, and J.A.
The air output is going to be about 85 to 95 deg from the heatpump. If more
than this you may be using the heat strips (electrical heaters in the air
ducts, often called emergency heat).
The heat output will be a constant value and the setting of the thermostat
will not make the air comming out of the ducts any hotter no mater what you
set the thermostat at. Over a long period of time the room temperature will
go up. When raising the thermostat more than about 3 degrees some heat
pumps will activate the heat strips and your energy usage will go up.
As mentioned, set the thermostat at one temperature and let it go at that.
YOu may cut it about 3 degrees at night. If you are not in the house for a
long period of time (say 8 hours) and have a timer on it, you may want to
set it back 3 degrees while you are out.
If you have the thermostat set for 67 and the temperature is 62 on the
thermostat, then you do have problems. The heat pump is probably not
working and you are probably running on the heat strips when you go to 75
deg on the thermostat.
Last night I had the thermostat set at 67 F all night. This
morning's outside temperature was 39 F. When I woke up at
about 7 AM, I set the thermostat one degree higher. at 68 F.
It's digital and so seems to tolerate this fine tuning well.
The heat pump came on immediately. The registers blew cool
air for maybe a minute or so, but then turned warm and
stayed warm. The warm air coming out was noticeably and
steadily warming the house, so I left the thermostat at 68 F
for 20 minutes or so. Then I raised it to 70 F. The heat
pump came on/continued on, blowing strictly warm air. Twenty
minutes later I raised the thermostat another three degrees.
The heat pump continued to work fine.
I never heard noises from the heat pump like I did yesterday
(after monkeying with the thermostat a lot), too.
The lesson from all my reading at the newsgroup and on the
net is that (1) a heat pump tends to have more "inertia" to
overcome (for its size) than a furnace (this includes
blowing the old cool air out of the ducting and getting the
refrigerant circulating until the correct system
temperatures are reached. Plus compressor speed and system
expansion valve setting has to change? All kinda slowing
things up compared to a gas furnace); (2) a possible defrost
cycle; (3) the "emergency" heat strip operation can confound
the heat pump control system response somewhat; and (4) a
heat pump is more of an "on-off" heat source than a
gas-fired furnace, because the flow of air and temperature
at output is pretty constant. The thermostat bumps the heat
pump on and off as needed. Whereas a furnace can crank out a
much wider variation of temperatures and maybe flows of air
(more natural gas/furnace burners lighting = higher temps
much more quickly)? Something like this, from my analysis
and folks's comments.
Ralph, I am definitely thinking about those heat strips. I
understand that, if possible, I want to avoid them coming on
so as to minimize electricity costs. The danged heat strips
just have no place in a heat pump "system" AFAIC anyway.
Technically they ain't no heat pump but instead a
modification and the ultimate in heating waste. Hopefully
through improved heat pump thermostat operation, I might
even see our electrical bills go down here.
Anyway, I am toasty warm here. I will post an update if I
note other changes. Thanks for helping me have a nice warm
house Xmas morning. Happy holidays to all.
Glad you are warm. The heat strips have 2 functions. One is when the heat
pump part breaks and you need heat. That is the emergency heat part.
When the temperature goes way low (somewhat below 20 deg F) the heat pump
becomes very inefficiant and the heat strips put out more heat per dollar
than the heat pump part .
This helps. Thanks!
I have been raising the thermostat steadily and it's now at
76 F. The heat pump is cranking out the heat just fine. Room
temperature is 75 and rising, by my best guess. Outside air
temp is undoubtedly rising as the morning progresses, too,
though, and no doubt this helps. The heat pump seems just
fine for my area (of course, given the many folks who have
them where I live).
Now I am getting confused. I'm the OP.
I have heard now that the low end efficiency falls off at between 20 and 35
degrees F. Which is it? Where I live, the max low is about 25 F.according
to US Weather records. And that for only about a month a year.
I am going to call my hvac guy after the holidays. We're doing an addition
anyway, and we'll be ready to fire up that one. I'm going to have him check
this system, all the ductwork, connections, etc. This system just doesn't
heat the house very well. But then, the house was enlarged, and the size of
the heat pump not increased. We use a wood stove for the large room
addition. At times, we just turn on the fan, and use the unit to
recirculate the warm air from the wood stove throughout the house. Still,
the house has cold rooms.
In a nutshell, it's a bag of snakes that's been Rube Goldberged together.
Now, for my next question: I have a friend who's a union electrician who
does all my work. I have one set of breakers where I can run a new line to
the heat strips, should the hvac guy say they will work. When the unit is
operating, does it need this additional power, or is the 220 line that is
running the unit adequate to run the unit and the heat strips? It would
seem that the unit would be running just the electrical strips and a fan
rather than the strips and the compressor. Am I right or wrong?
I know, I know, I should talk to the hvac guy, and I am going to right after
the holidays. I would just like to be somewhat informed when I do.
SteveB, not exactly sure what you are asking about the power
requirements. Normally, you have a 240volt circuit run to the outdoor
unit, ideally sized according to the information on the tag on the unit.
Then a separate 240 circuit to air handler to power the heat strips and
the blower, with the breaker and wire sized according to the size of the
heat strips, which can typically be between 3 and 20 Kw. A lot of units
with 15kw and larger strips have the strips split into 2 circuits. The
strips will come off and on with the outdoor unit running if the
thermostat determines they are needed. They also typically are energized
when the HP goes into defrost so it does not blow cold air.If the
thermostat is turned to "emer heat" , the outdoor unit does not run, and
the blower and heat strips are used, so that it operates just like a
regular electric heat system. Again, dunno if this answers you question
or not. Larry
Yes, it does. It sounds like I'll need another circuit just to power the
heat strips. I was wondering if one or the other worked at any one time,
like the heat strips OR the compressor, and, apparently, they run at the
same time, plus all the power draws of the blower.
Last night I set the thermostat at 68 degrees F. Overnight
the outside temperature got down to about 38 degrees F. I
woke up about 5 AM to a freezing house and cold air blowing
from the registers. I waited 15 minutes, and cold air was
still blowing out.
At the thermostat's thermometer, the room temperature
reading was 62 degrees F. I then turned off the heat pump.
Freezing my rear off, I pondered it all. I let ten minutes
go by, set the thermostat at 63 F, and then turned the heat
pump back on. Cool air blew out for a minute or so, and then
warm air followed, and the house warmed. Over an hour or so,
I raised the thermostat setting to 71 F or so. The house
continued to warm, and all was well.
The same HVAC technician that came out a few weeks ago came
out again today. This time he determined that the reversing
valve was sticking. Obtaining a new valve will take a week
or so. Meanwhile he said if cool air was blowing out again
when I wanted heat, then switch the thermostat from heat to
cool, and then back, and listen for a "swish" sound. This
might jar the valve free and cause it to open(?) properly.
Any advice on helping ensure my house has heat in the days
remaining until the new valve arrives and the tech can
install it? I will continue with the "gentle touch" when
raising the thermostat setting. Perhaps the mechanical
features of the valve respond better to less extreme
I know the basic function of the reversing valve. But I am
not sure whether it (1) throttles the refrigerant at all or;
(2) it's always wide open for heating mode, and wide open
for cooling mode, just directing the refrigerant flow in
opposite directions depending on the flow; or (3) switches
between the two directions when in heating mode, as a part
of the defrost feature?
I think understanding this might help my dealing with it in
the days before the repair. TIA for any light anyone can
shine on this. Meanwhile, I will google.
Elle, you are correct on #2 & 3. When a heat pump goes into defrost,
three things happen-- the reversing valve switches to the cooling mode,
the outdoor fan shuts off, and the OD unit sends a signal to the air
handler to turn of the heat strips to prevent it from blowing cold air.
Your valve may be sticking in the cool position. Hopefully the tech
carefully checked out the defrost controls and is sure that is the
problem. (replacement of a reversing valve is very expensive) On most
heat pumps, the valve is in the heat mode when there is no voltage to
the solenoid coil on the valve, and power to cool. For some reason,
Rheem/Ruud units are the opposite. They have to have power to heat. If
he found voltage to the coil, and the valve still in the cool mode,
then his diagnosis sounds correct. Good luck Larry
Hi Larry, the technician said he alternated voltage to the
reversing valve and found it sticking. He may very well have
done something more sophisticated (or simply what you
indicate above) but did not want to explain it (on his
admittedly valuable time) in too much detail to someone
unacquainted with heat pump systems.
A few weeks ago he did check the defrost controls, and, beg
pardon, replaced the defrost control board, though initially
claiming nothing was wrong. This happens to be the second
board in a year. I think the technician knows what he is
doing, since, as you suggest, the board is a lot less
expensive to replace, and they do fail often (from my
reading on the net). On the other hand, two in a year seems
excessive, and I wonder if the sticking reversing valve was
overlooked in both cases, so as to avoid the expense. I am
on a home warranty here for the heat pump, so I can't blame
them too much. I'd hope the cheaper item was the problem as
well, if I was DIYing it.
I think I follow what you mean (in your other post) about
what the tinkering s doing. It's maybe keeping the heat pump
from getting that 30, 60, or 90 minute signal to defrost. At
least, that's what I remember from reading on the net
earlier and a few comments from the technician on this. What
you propose does seem to explain the symptoms of the
problem. I will try again the "gentle touch" of just upping
the thermostat a degree from room temperature at a time,
starting around 5 AM, when no doubt again cold air will be
blowing due to the reversing valve being stuck in "cooling"
mode while defrosting. After that, as the sun rises, I think
I won't need defrost any longer for the day and will
continue to adjust the thermostat upwards every hour or so.
Or I will come up with some similar plan. It seems to me I
want to let it get into defrost mode and remove frost, then
deal with the valve sticking by cycling the controls a bit,
Thank you for sharing your experience. It helps a lot.
Forgot to add: normally, the valve on a Rheem should have power any time
the thermostat is turned to the heat position, regardless of the
temperature setting, Possibly your tinkering with the thermostat is
keeping the unit from running steadily enough to need to go into
defrost, preventing the problem. Ony other way to insure constant heat
is to run it in Emergeny Heat. That is what it is there for. Larry
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