Trying to figure out why the solenoid on the reversing valve is stuck.

[RandyRich]

I'm a second semester hvac student. Unfortunately, we haven't started heat pumps and mine is acting a little funny. The HP is a Trane XL 1200. The thermostat is a white-rogers.

In cooling mode I've always noticed that the reversing solenoid doesn't disengage until several minutes after the outside unit goes off. However, we just turned our ac on for a few days and now it isn't disengaging at all unless in heat mode. The solenoid gets it's power from somewhere other than the outside unit because it doesn't disengage even when power is cut to the outside unit.

Can anyone explain to me the mechanics of this? Where does the solenoid get it's power and what controls the device that feeds power to the solenoid? Please don't tell me what the problem is just yet, because I'm trying to figure it out on my own.

[bobb25]

You've got a low voltage solenoid coil.

[everythingair]

The reversing valve solenoid is an electro-magnetic valve that allows refrigerant into the pilot tubes that go into the ends of the reversing valve. What you are most likely experiencing is the time delay of the pressure of the refrigerant in the pilot tubes not moving the reversing valve rather then the solenoid not energizing or de-energizing.

Since the outdoor coil is colder during the winter operations, the refrigerant is not as high in pressure and would take longer to react in moving the reversing valve when the system is shut down.

[second opinion]

Your reversing valve is sent 24 volts from the Tstat.

[beenthere]

Have you replaced that stat since teh last time you used it in cooling mode.

[model m-man]

Hint - RV energizes only one way, either in cooling or heat.

[RandyRich]

Have you replaced that stat since teh last time you used it in cooling mode.

No. We bought the home 4 years ago and it's been there since then.

[RandyRich]

Hint - RV energizes only one way, either in cooling or heat.

This one energizes in cooling mode. When I turn the tstat to heat, it disengages, but in cooling mode it is not disengaging at all.

[buttwheat]

If it is a trane XL1200 heatpump from the late 80s or early 90s and 2 1/2 - 4 ton with an Alco ( blue one) valve it's the valve hanging up. They had a lot of problems with that.

[RandyRich]

The reversing valve solenoid is an electro-magnetic valve that allows refrigerant into the pilot tubes that go into the ends of the reversing valve. What you are most likely experiencing is the time delay of the pressure of the refrigerant in the pilot tubes not moving the reversing valve rather then the solenoid not energizing or de-energizing.

Since the outdoor coil is colder during the winter operations, the refrigerant is not as high in pressure and would take longer to react in moving the reversing valve when the system is shut down.


In this case the solenoid makes a humming sound when engaged. That's how we know that the valve takes a few minutes to disengage under normal circumstances, because you can hear a hum coming from the unit after it turns off. Now the hum is not going away unless we set the unit in heat mode.

[jeff520]

The solenoid can not hum unless there is power applied to it.

If it is humming, then it must be getting that power from the thermostat (normal operation) or there is a short somewhere in the wiring putting power to the solenoid circuit (NOT normal operation).

Could be the solenoid is a symptom and you heed to be looking elsewhere for the cause.

[RandyRich]

If it is a trane XL1200 heatpump from the late 80s or early 90s and 2 1/2 - 4 ton with an Alco ( blue one) valve it's the valve hanging up. They had a lot of problems with that.


BINGO! Yes, it's an ALCO valve. Still has a little blue on it. Trane xl1200 manufactured in 1986. But how could it be the valve hanging up if we are still hearing a hum (solenoid is engaged)? It seems like the solenoid is getting voltage when it shouldn't.

[bobb25]

The solenoid is an electrical coil. The piston inside the valve is mechanical. As long as there's electricity to the coil, it's going to try to pull that piston.

[RandyRich]

The solenoid can not hum unless there is power applied to it.

If it is humming, then it must be getting that power from the thermostat (normal operation) or there is a short somewhere in the wiring putting power to the solenoid circuit (NOT normal operation).

Could be the solenoid is a symptom and you heed to be looking elsewhere for the cause.


I think that might just be the problem. I'm going to see if I can find a wiring diagram for this thermostat. It's an old White-Rodgers model 3298-A (i think) Digital Comfort Set II programmable for heat pump. I looked on their website but couldn't find anything.

I'd like to know which 2 wires control the solenoid valve. When I know that, I should be able to disconnect them and see if the thermostat is calling for the solenoid valve continuously. If so, I would think the thermostat needs replacing. Would you agree?

[jeff520]

I think you are getting too close to a DIY discussion, rather than a general discussion about a problem. Maybe someone here would tell you which wire it is, but as a second semester HVAC student you should be able to follow and identify wires, and you certainly should be using the expertise of your instructors, who would probably view this as a good teaching opportunity.

[t527ed]

solenoid should drop out if you switch stat from cool to off, have you tried that??????


may be wired so energized when switch is in cool position whether calling for cooling or not.....:cool:

[gevans]

what t527ed said.

[RandyRich]

solenoid should drop out if you switch stat from cool to off, have you tried that??????


may be wired so energized when switch is in cool position whether calling for cooling or not.....:cool:


When in cool the solenoid engages. When you turn the thermostat to the off position, the solenoid stays energized. When you go to heat it de-energizes.:eek:

[RandyRich]

I think you are getting too close to a DIY discussion, rather than a general discussion about a problem. Maybe someone here would tell you which wire it is, but as a second semester HVAC student you should be able to follow and identify wires, and you certainly should be using the expertise of your instructors, who would probably view this as a good teaching opportunity.

I'm sure all schools are different but we covered refrigeration in the first semester and are covering the electrical system in this one which started a month ago. We've touched on the basics of how a system is wired but haven't got real detailed yet. We haven't covered the thermostat at all and heat pumps are reserved for another semester altogether.

I have class on Monday and Wednesday nights. I plan to ask him tonight.

Thanks for your help.

[Swampfox]

When in cool the solenoid engages. When you turn the thermostat to the off position, the solenoid stays energized. When you go to heat it de-energizes.:eek:

I think you are mistaken, the RV coil will be energized whenever the thermostat is set to the cool position, calling for cooling or not, when you turn the thermostat off it will de-energize the valve but it will not shift until there is a pressure differential, thats why your hearing it shift when you turn it on in heat mode.

[rakes9720]

Some thermostats (digital) will leave the reversing valve in the last position (heat or cool) when you turn the mode to off. This prevents excessive cycling of the valve. For example, in the summer on a hot day, you turn it to cool. Another day, its not hot, so you turn it to off. Later it gets hot again, so you switch it to cool. This would normally cycle the valve 3 times, but some thermostats will not turn off the valve unless you go back to heat.

And the solenoid will be energized constantly when the switch is in cooling mode.

[Swampfox]

Every digital I have seen does not do this, just because the valve is energized or de-energized does not mean it will physically shift, there has to be a pressure differential also, the solenoid only actuates a pilot valve assembly, pressure moves the valve itself.

[beachtech]

there has to be at least 70 psig differential for a switch over valve to move :)

[RandyRich]

Some thermostats (digital) will leave the reversing valve in the last position (heat or cool) when you turn the mode to off. This prevents excessive cycling of the valve. For example, in the summer on a hot day, you turn it to cool. Another day, its not hot, so you turn it to off. Later it gets hot again, so you switch it to cool. This would normally cycle the valve 3 times, but some thermostats will not turn off the valve unless you go back to heat.

And the solenoid will be energized constantly when the switch is in cooling mode.

You may be right. I checked with my instructor tonight and he said the solenoid can stay engaged while in the cool position (i.e. not disengage until you go to the off or heat position). He did say that it should disengage when you go to the off position. He also said that it does no harm to the solenoid to be constantly engaged.

[beachtech]

You may be right. I checked with my instructor tonight and he said the solenoid can stay engaged while in the cool position (i.e. not disengage until you go to the off or heat position). He did say that it should disengage when you go to the off position. He also said that it does no harm to the solenoid to be constantly engaged.

he is right :) and some thermostats turn power of to the reversing valve after each cooling call, but then you may get some noise complaints :D

[Swampfox]

The old Goodman digitals did that, and they short cycled like crazy too, talk about noise complaints lol

very few thermostats de-energize the valve every time the call for cooling is satisfied

[beachtech]

well lmao goodman has not been known for a quiet system at least not during the bristol days :)

[rakes9720]

some thermostats turn power of to the reversing valve after each cooling call, but then you may get some noise complaints :D

My neighbor's (3 houses down) does that and it is annoying. Then they got a new carrier heat pump, and the installers left the same thermostat and it is still annoying, even with the quiet compressor.