Heat Pump Operation

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; no luck.
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On Mon, 24 Dec 2007 08:45:01 -0700, "Elle"

     Ellie, 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 correctly. 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. Bubba
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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 body temperature.
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.
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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 morning.
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 conditioning unit.
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.
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wrote

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.
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Update:
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.
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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 .
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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).
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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.
Steve
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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
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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.
Steve
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Heat pumps blow colder hot air than a regular furnace will. Some folks (like me) hate heat pumps. If it bothers you that much, can the HP and get a real furnace. That's what I did.
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Further update: 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 electrical signals?
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.
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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
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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, worst case.
Thank you for sharing your experience. It helps a lot.
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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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