6yr old Lennox heat pump

[elmonducky]

unit will not switch over to heat. Found no power at t-stat from red to blue (reversing coil). Power to all other wires (white yellow and green)  With unit in off position found reversing valve vibrating and hot. Had 27 volts to coil when unit off. Removed wires from coil and now it works in heat.  I understand that coil should be in heat mode when not energized but cant understand why I would have 27 volts when not turned on and why it would even reverse with only 27 volts, I think coil is 120 volt.  Also dont understand why I have  no power to blue wire at t-stat.  Assume one of my relays is stuck.  No problem with heat for the season but need to get corrected.

[Cactus Bob]

sounds like you reversing valve is working fine , its coil is 24vac  and will have have power any time your thermostat is set for cooling , even if the unit is not running ...... without being there i would guess you have a broken blue wire or a bad defrost control board .... if you do not get it fixed  your outside unit will freeze up and you will loose heat ....... first thing i would do is hook up the reversing valve , set on heat and start unit , then jump the red and the blue wires at the outside unit and see if the reversing valve switches to heat .

 if that works then its a wire problem if not its the board

[elmonducky]

Thanks, I will try that.  Im not too worried about it freezing up I live in Scottsdale Az.  Im curious though, why would I have power to the coil when the thermostat is off?

[Cactus Bob]

trust me it will freeze up , i am in apache junction and repair frozen up heat pumps every year . we do have enough moisture in the air in the winter to make them freeze .  but if you turn it off and wait for the sun to hit the unit ,it defrosts real quick .

[ACtechGUY]

The reason you have power at the reversing valve is to prevent the switchover noise (WOOSH!!!) every time cooling stops. Terminal O in the thermistat provides power to the valve.

In a call for cool O and Y will have power.

In a call for heat There will be no power on O.

[elmonducky]

Interesting, I guess you would get the swoosh then everytime the heat goes off? 

[ACtechGUY]

No, because the valve is not powered in heat mode there is no switchover that happens. The woosh noise would occur only after the shutdown of cooling. If that happens or not depends on what the thermostat or control board is capable of doing.

The sound occours when Hot high pressure gas rushes into to the pipe leaving the condenser that was occupied by low pressure cool gas in the cooling mode.

If you let me know what color wires go to what terminals at the thermostat, I may be able to suggest what to check for.

[elmonducky]

red-green-white-yellow-blue.  I have 27volts from red to all the others except blue in heat or cool

[ACtechGUY]

I need to know how they are labled at the thermostat . R=red

w= white g=green ect. also where are you reading these voltages ?

[elmonducky]

corresponding, from the r terminal with the red wire to the w terminal with the white wire and so forth. Only from red to blue do I not have voltage. This is with t-stat in off position.

[elmonducky]

I assume I have a break in my blue wire somewhere from my t-stat up to my A/C unit but have not had a chance to jump from red to blue up at the A/c yet.

[ACtechGUY]

Sounds like you are checking voltage to ground. You need to check from the 24 volt common wire to the other wires. There should only be voltage between 24 volt hot (red) and common wire at condenser with stat turned off. The best way to find wire colors along with the letter codes is at the thermostat base.

The reversing valve is controlled by the O output ( usually an orange wire)

[elmonducky]

Like I mentioned I am checking voltage from t-stat terminals to the other terminals. Unless those terminals go to ground. Are U referring to neutral? I am checking at the t-stat base. This A/C uses a blue wire instead of an orange for the reversing valve. I'm actually an appliance tech but have been to refrigeration school and did a/c work for a few years quite some years ago. I realize some things have changed over the years such as the use of P.c. boards and what not but t-stats seem to be relatively the same as yesteryear.

[elmonducky]

The t-stat im using is a programable one that allows U access to the terminals without disconnecting the control. The terminals actually are located at the top. So u can still test the terminals with the control set to different functions.

[ACtechGUY]

You must check for voltage from the common (C terminal ) to other wires. Checking to R terminal is not correct.

The best place to check is at the condenser. Check between the common (whatever color that turns out to be and blue (O).

With a call for cool : R TO C 24volt ---- C to Y 24volt ----- C to O 24volt ----C to W 0 volt ----

Call for heat : R TO C 24volt ---- C to Y 24volt------- C to O 0volt ----C to W 0 volt(unless in defrost) ----

disconnect blue wire at stat and bring on heat. if condense starts blowing cold then your stat is not configured to operate a heat pump or is bad.

[elmonducky]

I will give that a try, thanks. Just out of curiosity is the common or c terminal neutral or 24volts. and how is it either if there is no wire connected to it???

[ACtechGUY]

The Common is the other side of a 24 volt transformer. You can think of it as a neutral, but it is not the same as checking from any of the wires to a true ground. checking to ground is no good either.

You probably do not have a common wire to your tstat. If it is battery powered or use plain old you would not have the wire connected at the stat. You must find the common at the condenser. and test using that wire. that will be the only way to find your problem.