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Heat Pump reversing Valves (Take Two!)

Heat Pump Reversing Valves
, what are they, and how do they work?

The heat pump reversing valve; this simple device causes almost as much confusion as defrost controls. Based on appearance alone the confusion is understandable, if not outright scary...

The purpose of the reversing valve is to swap the refrigerant lines going to the compressor's suction line and discharge line; making the indoor coil the condenser, and the outdoor coil the evaporator.

The valve has four tubing connections; three outlets on the top, and one inlet on the bottom. The bottom is always connected to the compressors discharge port, and the top, center port is always connected to the compressors suction port. One of the remaining two top outlet ports connects to the suction tube going to the indoor coil, and the other connects to the hot gas discharge tube going to the outdoor coil.  

Inside the body of the reversing valve is a sliding piston that has ports in it.  Sliding the piston to one side or the other connects the hot gas and suction ports from the compressor to either the indoor or outdoor coils allowing the coils to swap functions.

How does the piston move? A small capillary tube runs from the compressor hot gas port (bottom port) to the solenoid valve attached to the reversing valve. Hot gas is directed to one side or the other of the piston, this sides the piston back and forth. The direction the piston moves depends on whether the solenoid is energized or not.

This is where the "O" and "B" terminals on a heat pump come into play. Equipment that uses an "O" thermostat energizes the solenoid for cooling, while equipment that uses "B" energizes the valve for heating operation. The only difference is the way the valve is piped in.

Now that we know what a reversing valve is and how it works, let's look at how it can fail. Keep in mind the only serviceable part on the reversing valve is the solenoid coil; all other failures require replacing the whole valve.  Typical reversing valve failures are:

  1. ·       Failed solenoid coil
  2. ·       Refrigerant leak
  3. ·       Sticking in one position (heat or cool)
  4. ·       Sticking mid travel
  5. ·       Internal seals leaking by

#1- Determining if the solenoid coil is bad is easy; first the compressor must be running and there must be a pressure difference between the high and low side of the system (the valve shifts due to pressure differential) if the valve doesn't shift when power is applied or removed to the coil, ohm out the coil. If it's open, replace the coil, if the coil ohms out ok, replace the entire valve.

#2- A leaking valve is easy to, if the valve is leaking, replace it. Don't try to repair a leaking valve.             

#3- The check out procedure for a stuck valve is the same as the check out for the solenoid coil.

#4- Diagnosing a valve that's stuck mid-travel is a little trickier; the systems high and low side pressures will be close to the same, the refrigerant lines at the reversing valve and at the compressor will be warm to hot, and the compressor usually makes a loud, growling sound; like a scroll running in the wrong direction.

Be careful; a valve that's stuck mid stroke can be mistaken for a failed compressor, or a metering device (bypassing psiton, or TXV) that's stuck open.  If the metering device is stuck open the compressor's suction line will be cold, and its discharge line will be warm. An easy check is to close the liquid line service valve to see if the system will pump down.

#5- A reversing valve that's leaking by internally will still function, but the suction pressure will be slightly high, and the system will loose capacity. This is a relatively easy problem to diagnose: Start the system and let it run about 15 minutes (it doesnt matter if its heating or cooling mode) then measure the temperature of the two suction ports on the valve, there should be less than 5 degrees difference.

Helpful Tips-

Never hit a reversing valve with a wrench, hammer, or anything else. If you do, and wasn't bad before, it probably is now.

If you need to replace a reversing valve, remove the old valve by cutting the lines a few inches away from the valve, in an area that you can acceess with a torch. (Use a tubing cutter, never use a hack saw). Mark how the tubes are inserted in the valve and un-sweat them. Wrap the new valve with a damp cloth and braze the tubes into the valves stubs.   Use slip couplings to install the valve in the unit. This helps prevent overheating the valve.


+2 # Glenn 2011-09-02 23:44
Where you talk about checking a stuck valve you say the discharge and suction will be cooler at the reversing valve than at the compressor. What are you saying here? compressor not pumping, stuck valve or open metering device. This whole paragraph is a little confusing the way it is worded everything is all run together. Some clarification would be nice.
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+3 # ZenMaster 2011-09-03 17:49
Glenn is right to call us out on this one; it's long winded, somewhat confusing, and could be better...much better. This will be revised before the weekend is out.

Glenn, we appreciate the honest feedback; it's what we need to make sure the information here is useful to everyone.
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+3 # ZenMaster 2011-09-03 20:39
Ok, this is our first revision. We added a picture of a cut apart valve with the piston removed to give you an idea of what's going on inside. We cleaned up the wording and broke the mile long paragraphs into more readable 1/4 mile long chunks.
If anyone has a sugestion on how to further improve this, speak up. (that includes you Glenn!) :-)
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+4 # Glenn 2011-09-03 23:15
In #4 you say close the liquid line valve to see if the system will pump down. Does this mean the compressor is good, something is stuck open or just what? I'm not trying to pick your information a part I'm just trying to make sure I understand what you are saying. It sounds much better than it did before. Also is there anyway your site could have a printer friendly version so your information could be printed off without all he extra stuff.
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+1 # ZenMaster 2011-09-04 09:19
If the system pumps down it means the compressor is good (maybe not 100% but it's doing something) and the reversing valve isn't hung-up mid stroke; it's probably the metering device is stuck open or is bypassing.
As far as making the content printer friendly, I'll check with Kevin, he's Zen's site guru.
And we don't mind your questions at all, keep them coming.
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+3 # Larry 2011-09-24 01:11
How does the solenoid coil come off. Please explain.

Thank you,
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0 # ZenMaster 2011-09-24 08:43
Hello Larry,
The most common style has a 5/16" hex head screw holding the coil on the valve stem.
Some models have a cap or 'button' retainer that snaps onto the stem.
Some older ones had a spring wire clip.
After removing whatever is retaining the coil, it should slide off the valve stem.

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0 # Art Wallace 2013-06-12 17:51
After removing the coil, should you be able to slide the stem back and forth with your hand? Is the stem supposed to move?? Or is it something inside the stem itself that moves (that you can't see even with the coil off)? Thanks!
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0 # Richard 2011-10-12 17:27
what is a slip coupling as mentioned i n reversing valves installation
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0 # ZenMaster 2011-11-06 22:20
Sorry for the delayed response Richard.
A slip coupling is a copper sweat coupling that does not have a dimple or shoulder formed in the middle. This enable the coupling to slide all the way over a pipe. In short, it makes it easier to position the new valve in place without bending the piping.

We appreciate the comment.

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+1 # Jacob 2011-11-24 03:32
I have a carrier heat pump about 4 years old and when it first starts up it sounds like the compressor enguages twice one when it first comes on and again about a 30 seconds later but it heats fine could this b the reversing valve
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0 # Zenmaster 2011-11-24 11:26
Good question Jacob, and good news! Your reversing valve is probably fine; some Carrier and Bryant heat pumps have a feature called "quiet-shift".
Quiet shift shuts the compressor off as the reversing valve shifts into the defrost position; this lessens the loud WOOoooSH noise and the compressor growl noise.
30seconds after the valve shifts the compressor is restarted.

If the starting and stopping bothers you the feature can be disabled via a dip switch on the defrost board, or if it's an Infinity system in the advanced setup menu's.

Have a good thanksgiving!

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+3 # Chris 2012-03-23 06:25
Hi, I'm not sure if this is the right thread or if I should start a new one but here goes;
I have a split unit heat pump and when I call for cool in the house it pulls warmish and the outside unit is cooling, seems a reversing valve problem which made me look at your site. Now at the same time the outside fan does not come on so I am wondering:
If the valve or solenoid is broken would this also cause the fan not to work or

Is this maybe a thermostat problem or

Just coincidently seperate problems or?

I am really struggling with this and the only advice I get seems to be based on guesswork and replacing bits on a guess. I'd really appreciate some advice based upon analysis. Thanks
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-3 # patrick peterson 2012-03-25 10:09
A failed reversing valve wouldn't cause the condenser fan to fail,
neither would a T-Stat problem.
It almost sounds like a failed outdoor fan motor/capacitor or failed
defrost board relay.
First, lets determine if the unit is actually in cooling mode. If the
thermostat uses a 'O' terminal there should be 24 volts on 'Y' and 'O'.
If it uses a 'B' terminal there should only be 24 volts on 'Y'.
Let me know and we can take it from there. Also, what brand unit is it?

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0 # dijon 2012-04-04 00:38
my heat pump worx fine most the yr. until the warm season comes and i switch to cool. i get loud gurgling for some minutes then it quiets and no cooling. have to recharge every spring or summer. theyve done done various services each time but i dont believe they fixed the root cause. which i suspect is a bad reversing valve that leaks when it switches to cooling mode. any other ideas? or do u agree?
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0 # Jeremy 2012-05-27 11:21
Ihave a heat pump system that doesnt seem to wanna pump down. My purpose needing to do this is to relocate unit. Should i have energized the reversing valve in the pump down procedure? I valved off high side without unit running and began pump down when realizing system would not pump down. Is it possible ive pumped everything into the line set and a-coil and cant get system to restart because of compressor fighting against to much pressure? if so is a hard start kit suitable to use for a start up in this situation?
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-4 # Isaac 2012-06-13 10:34
This is helpful. We have been trying to figure out what is busted on our AC unit. It stops cooling when it rains, but no icing on the evaporator coil, the condenser fan and condenser sound like they are running, but coolish air, not hot, is blowing off the outdoor unit and the indoor coil is lukewarm to the touch. This morning I found that the control wiring outside has damaged insulation on multiple wires, and I wrapped them individually with el. tape and then wrapped the whole bundle multiple times.
Is it possible we have a "B" system and the rain was causing the solenoid to energize? I did not know about reversing valves this morning.
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+2 # vhehn 2012-06-13 21:59
hi i have a heat pump that will not cool. it is stuck in heat mode. when i jumper the reversing valve it cools so i know the valve is working. it seems to indicate a bad defrost board. can a bad defrost board cause no cool?
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-1 # oren 2012-12-20 08:32
Hello Zenmaster:I have a question for you if you don't mind. My 2.5 ton nutone heat pump which is only 3 yrs old worked fine thru the summer but now that cooler weather is here it seems not to be putting out warm air. I have noticed the coil around the unit has been freezing up with a sheet of ice. Also i cannot hear the familiar wooshing noise that i use to hear when the unit goes in to defrost mode. Do you think this could be a faulty coil on the reversing valve(hopefully and not the valve itself.) thanks
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+1 # patrick peterson 2012-12-23 21:23
If your thermostat uses the 'O' terminal, try running it in cooling; if it cools, the reversing valve coil is good. In that case its most likely the coil temperature sensor.

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+1 # Billy 2013-01-02 22:33
I am working on a 2 1/2 ton ComfrontMaker split system R22 heat pump system. Suction pressure was 100 psig head pressure was 150 psig. Clean indoor coil clean outdoor coil. I was told it was a TXV problem so i changed the TXV. still have the same problem. I have 66 degrees F coming out of the registers and around 76 degrees F at the return. No subcooling and no superheat. Any help would be greatly appreciated.
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0 # patrick peterson 2013-01-05 10:30

Heat pumps have an outdoor metering device for heating operation- either a txv with a bypass check valve installed or a sliding piston meters in the heat mode and is bypassed in the cool mode.

I'm guessing that the bypass check valve (or sliding piston) is stuck open (the cooling position).
If it runs ok in the cooing mode, this is likely the culprit.

Let me know what you find.

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0 # juan eric 2013-10-29 17:36
its the expansion valve
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0 # Joe kadima 2013-02-05 17:37
hi sir,im working in 40000btu heat pump split. it not cooling at all and no heating when set at heat mode,after checking i found the system is chowing the same reading on suction and discharging (90 psi) after replacing a new compressor the situation is still the same. tell me that can be the reversing valve which is faulty? how to proceed? thx, J. kadima
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0 # patrick peterson 2013-02-23 23:00
it may bed a stuck reversing valve or a stuck metering device bypass.

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-1 # john kramer 2013-02-05 22:22
I have a Trane heat pump. It runs in cool mode but will not in heat mode. To be more specific, once in a few starts it will run in heat mode for less than one minute and shuts down. If left on it once in a while will cycle back on for another 30-60 seconds. I've metered the 24v R-B and it seems constant. In cool more there is 24v (27 actually) R-B and Y-B. The LED on the outside unit flashes once per second as it should. Any suggestions? Would running in heat mode be more likely to shut down due to low pressure?

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0 # patrick peterson 2013-02-23 22:56
Heat pumps normally use a lose of charge switch instead of a low pressure switch (not always, but often) does the compressor, fan,....everything shut down, or just the compressor?
In a nutshell; without more information I can't say what's wrong.
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+1 # Tonie 2013-02-15 12:30
Hey there, appriciate this understanding of how reversing valves work and their purpose but from you experience why do they fail? Could it be from too much or not enough refrigerant?
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0 # patrick peterson 2013-02-23 22:16
Good question Tonie.
I don't see them fail to often. Usually they stick due to plugged ports and capillaries from burn out related gunk and debris, or their coils fail.
I've also run across a few with broken slide rings, but I cant say why they broke.

If anyone out there has an answer let us know.
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+1 # josh 2013-02-20 15:17
I was just wondering what the difference between a four capillary reversing valve and a three capillary reversing valve.
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0 # Patrick Peterson 2013-02-20 18:40
Good observation!
Some valves use a fourth capillary tube that connects to the true suction port. They use this to bleed off the high pressure gas inside the valve body so the piston can slide. Some valves bleed off the high pressure using a bleed hole in the slide valve piston, those types only have three capillary tubes, both styles still basically work the same.

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0 # tino 2013-03-02 08:58
hello, i have a coleman split system heat pump unit. the problem i am having is kinda weird to me but may not be for you experts. in heat mode the system will run but begin to frost at indoor txv some on the line before and after the txv onto some of the coil itself, untill i hear a loud Pshhht noise then all frost is removed and it heats fine. it goes through these events each time the unit starts up. i am wandering if its the reversing vavle or maybe defrost board or maybe somthing else.
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0 # Brian 2013-03-15 09:31
Greetings, and thanks for your blog. I have a heat pump (Payne 2 ton with TXV inside and 52 piston outside). When in heat mode, the condenser cycles constantly - on for 20 seconds, then off for 10, then on for 20 seconds and so forth. I have replaced the thermostat, and ensured the correct control wires are energized in heat mode. Cooling mode runs without a problem. Does it sound like the exterior piston, the reversing valve, or something else? Thanks for your insight.
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0 # patrick peterson 2013-03-19 22:22
some older 410A systems had a pressure switch that would shut off the outdoor fan if the head pressure climbed too high when it was in the heat mode. Why?
Because when the unit is in heat pump mode the outdoor coil is the evaporator, so shutting off the outdoor fan reduces the heat load, which in turn reduces the head pressure. I'm not sure if Payne had this feature or not. The other cause could be the defrost control or the fan motor itself. I would start by checking the voltage to the motor; if it's constant, its a motor or capacitor issue. If the power cycles it could be a defrost control issue.

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0 # Shawn 2013-03-19 17:55
I have a split system plus 90 furnace and heat pump. Every once in a while when calling heat the heat pump will actually be cooling instead of heating. If I power down the system and restart in will begin to heat in when calling heat. What would be causing this? Thanks for the help!
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+1 # patrick peterson 2013-03-19 22:09
I would start by checking the voltage going to the reversing valve Shawn.
If the unit uses an "O" terminal, the valve should not be powered during a heat call unless it is in defrost. If the valve is energized it's likely either the defrost control is stuck in defrost mode or the thermostat energizing the reversing valve.
If the system uses a "B" terminal the valve should be energized in heat mode. If it's not, the thermostat or the defrost control is the culprit.

Being that it only happens occasionally, I'm guessing it's either pitted contacts on the defrost board ("B" terminal system) or a failing "B" output on the thermostat (again "B" terminal system) that is not allowing voltage to the valve.

Let me know what you find. If you write back, include the equipment brand.

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-1 # Randy 2013-03-24 09:43
I have a 9yr. old heat pump. Heats/cools fine except now and then the compressor sounds like a diesel engine idling, and heat/cooling capacity is reduced some. Happend first in summer and again this winter. I disabled defrost circuit and use electric strips in below 30 or humid nights. locked in heat only mode, it has been quiet and performed well for 30 days in February, even at 28 outdoors. Do you think the r.valve is leaking? I could not feel any temp difference on my hand when it was noisy and the amperage was 11.5 same as when it is quiet. 4-ton. Also is there going to be a replacement freon for us r-22 guys available?
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0 # rakesh06 2013-04-06 09:21
hi we has a chiller Mc quay ,we has just repair a leakage on the discharge pipe before the 4 way valve . after repair how its sound to has a interna leakage in the 4way valve ,Do u thick this could cause by carbon during brazing ? could we repair it ? and there 2 big 4way valve in paralle thx
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+1 # Michael McCreary 2013-06-04 20:38
Ok, here we go. I have a VW air cooled engine with A/C. Yep, that's right! It is a nice old 1982 Cimbria SS Gull Wing Coupe. A VW on Steroids, Now I am removing all the heat exchanger stuff and want to install a reversing valve for heat hooked up to a 12vdc inverter to 110vac to a 24vac transformer to run the valve. Unless you can put a 12vdc coil / solinoid on it for me! That would make it much easier. Can you do that for me so I don't have to wire up all that inverter/tranformer and then switch the power to energize the valve? Is there a problem with what I have in mind? Do you think it will work? I will be using an old R12 pump converted to R134. Being the car is 32 years old, a new receiver dryer will be installed. Now that brings up another question. How will the expansion valve that is in line at the condensation coils in the cab under dash? Do I need to work some sort of Einstine equation for that? :lol: Please help. Michael in a hurry. Henry NE.
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0 # Patrick Peterson 2013-06-04 21:42
Very cool, very cool indeed!
I had a Baja bug way back when, needless to say I got used to not having heat...
I would check out RV heat pump manufacturers, they may have a 12 volt valve. As far as the metering device, you will need one for each coil along with a bypass check valve, again an RV unit may have what you need.
Other concerns are defrost and making sure the inside coil can handle condenser pressures when in the heat mode.

Good luck Dude!
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0 # J Johansen 2013-10-05 18:50
I had a new Heat Pump installed about 2 months ago, Goodman 2.5 ton. After a couple of weeks it started to freeze up after running for awhile but if I would keep the fan on "on" not "auto" it would not freeze up. I had a technician look at it and Freon is good and he sees no problems. His best guess was to change out the inside TXV valve. He had said that it could have went bad if it had gotten too hot when brazing the lines in. I know that the person that installed the unit had a wet rag on the line but am not sure if he had it wet or cold enough or if he heated the line excessively. The valve is still on order but today it was cold (52 degrees) so I turned it to heat and the line gets excessively hot, up to 165 to 170 degrees and puts out about 150 degree air.I turned it to emergency heat and that is about 135 to 140 degree air which I think is normal. I am not sure if the inside TXV is bad or if both the inside and outside valve are bad or something else.
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0 # Scott Crumbly 2013-11-26 12:59
I have a unit r22 that has high head pressure(400) and high suction side does that sound like reverse is stuck in the middle?
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+1 # johnathon 2014-05-18 13:07
Can I bypass a reversing valve solenoid ? It is energized in cooling.
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0 # jcampbell 2014-06-18 05:47
Heat pump with two compresors and two reverse valves .has had been running with one compressor due to the other compresor windngs shorted to shell. But udually manages load well.I dont dee txv.now unit suction line temp is 70 - 80 degrees.pteasures look well 250/75 if I swich to jeat at reverse valve then back to cool ot starts at 50 degrees line temp but then gradually climbs back to 70 plus degrees. Older r 22 roogtop psckage unit. :zzz
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-1 # Ray 2014-06-22 19:06
Trouble with the 24 volt system. First time blew the 5 amp fuse and next time burned out the primary of the transformer. Reversing coil checks at 17.2 ohms and all the 22 volt dc heating relays check ok. Unit is a carrier 5 ton unit with reversing coil energized on cooling. No idea as to what would cause the primary of the transformer to go up in smoke as soon as power was turned back on. All help is appreciated.
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