Question about Ruud Defrost Control Board 47-102684-08 Rheem Weatherking 1157-121

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Heat pump kicks out for "Low pressure switch open." Indicated by the leds on the defrost control board Happens 2 times and then shuts down for " Low pressure lockout"

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Have you checked the pressures? if you have is it just the suction pressure low or are both the suction & the head pressure low? you could have multiple things cause that ex. low in freon, restriction, bad low pressure switch, bad board. If you don't know what your doing call a service tech. the LOW pressure lockout is a safety to prevent damage to your compressor.

Posted on Oct 15, 2013


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Posted on Jan 02, 2017



  • 1 Answer

SOURCE: RUUD Central Air/Heat Pump

if it runs with the test button it's not getting a call from the stat.
check for 24 v. from common (brown) to yellow. that should give you cooling add 24 v. from common to 'B' ( blue) for heat

Posted on Oct 25, 2009


  • 54 Answers

SOURCE: RUUD Central Air/Heat Pump

Start with the simplest first it,s not fun but it's necessary EVERY TIME. Clean your evaporator and condenser coil, change your air filter. Getting to the evap. coil is often a real headache and a result doesn't get done often. When its clogged as you probably know the refrigerant can't absorb heat at the coil so it tries to absorb heat on the way to the compressor freezing the hot gas line the safety circuits that protect the heat pump compressor from getting liquid refrigerant back to the compressor almost immediately will take the compressor of line (looking somewhat like a defrost cycle). I hope this helps it's a tough repair GL!

Posted on Jun 08, 2008


  • 99 Answers

SOURCE: My heat pump will not come on in HEAT or A/C. I

Hi; Need more info. How old is the equipment,look on the outside unit data plate it will give the built date usually in the top right corner. Also heat pumps can run with a faulty defrost board. I would check for control voltage at the secondary side of the transformer should be atleast 24 volts ac. Also the test post on the defrost board are for troubleshooting a defrost problem not an operational problem.When the posts are temporarely shorted the condensor will go into a defrost cycle This step will let the tech. know if defrost is operating normally. Also I have seen a reset switch manualy reset but not reinergize the control voltage. Also the outdoor unit has a delay timer that will wait for freon press. to equalize befor letting the unit operate. One more thing do You now if Your tstat is operating normally. One more idea is the defrost sensor if faulty it can leave the condensor in a defrost state of operation. This intern will sometimes go to heat strips because they are used in the defrost cycle to warm up the air conditioning going on durring a defrost cycle. One more thought is does the control contactor have 24 to 27 volts going to it if so replace the contactor. To test this using a voltage meter and touch after waiting 5 min. both sides of the coil. Remember voltage is deadly so ..When in doubt call a qualified tech.I ASSUME NO LIABILITY FOR INJURIES TO YOU OR THE EQUIPMENT BE CAREFULL!!! IF YOU GROUND YOURSELF BETWEEN 230VOLTS THIS BE VERY BAD...alpharome416

Posted on Jan 23, 2010


  • 59 Answers

SOURCE: My rudd Heat pump upka043jaz condensor is iceing

Either defrost board, low on charge, thermostat at coil, or reversing valve

Posted on Dec 24, 2010

Brian Mills

  • 613 Answers

SOURCE: Ruud Heat Pump

Check to see if there's low voltage reaching the contactor's coil. If there is. and it doesn't close (pull in), then it's defective and should be replaced. Cut the power and check ohms to be certain.

Posted on Aug 30, 2013

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I have an armstrong heat pump and am curious about how the defrost cycle works.

Rather lengthy but here it is.
The outside unit(heat pump) has a reversing valve, a defrost board, a crankcase heater, a metering device(txv or piston) and an accumulator. This is what makes it a heat pump instead of a straight air condensing unit.
When in the heat mode the outside unit becomes the evaporator and the inside unit becomes the condensing unit.Before somebody corrects me i am just stating what is different in a heat pump.
When the system goes into defrost several things happen. First the system has to call for a defrost cycle. This happens on a time and temperature sequence. When the defrost board times out for a defrost check(the defrost board has a jumper pin to determine how long before the system will check for a temperature(thermal switch) is open or closed. This switch is in the normally open position. It will close at 35 degrees(depends on the switch). This switch is located on the copper line in the condensing unit. If this switch is closed then the system will go into defrost. Now for the good part. This will shut down the outside fan, switch the reversing valve, and the outside unit will essentially go into cool mode. Because the fan is off the compressor will heat up very rapidly and the refrigerant passing thru the coils will be hot as well. This will cause the ice buildup on the outside unit to melt(defrost). This will continue until a temperature is met or it times out. Then the system will return to the heat cycle. One other thing, depending on how your system is wired the inside unit will turn on the auxillary heat while the defrost cycle is in process. That way you will still have heat while the defrost cycle is in process.
It is not uncommon for steam to come out of your outside unit while this is going on. It can also be quiet noisey sometimes.
Hope this explains what you wanted to know. If not just reply to this with any other question you have about the cycle.

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If compressor stops in middle, check the following.
1.Thermostat setting must be minimum +3 degree than your room temp
2. Check it's in heat "mode"
3. Check indoor and outdoor coils are clean.
4. Check fan motor is working alright.
5. Outside sensor and room air sensor is placed correctly.
6. Gas pressure is o.k
7.Check compressor is overheated, even all the above is o.k.

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If you can manually push in on the contactor and the fan runs, your not getting 24 volts across the contactor coil.
If the contactor is not energized, your compressor want be running, the contactor controls the fan and compressor.
You need to measure the voltage across the contactor coil and if you don't have 24 volts then you need to either jumper the pressure swiches or measure the voltage across the pressure switches if you read 24 volts then they are open.
If low pressure switch is open you are probably low on refrigerant, if high pressure switch is open it's bad.
If these check out ok then you might check the low voltage wires for loose connections or the wires from unit back to house and under the house to see if there's any breaks or insulation chewed up from lawn mower or animals.

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On a coleman heat pump DRHS0421CB when the thermostat call for heat the heat pump compressor and fan start for an instant and then they stop and a failure message shows up on the thermostat. This works the...

If both the fan and compressor are going off the problem would be in the low voltage side a safety is opening. Probably low on refrigerant. You need to check refrigerant pressure when the unit is starting, if the pressure drops below 60 psig the low pressure switch will open and shut the compressor and fan off.
You really need to have a service technician check the system out for you.

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Defrost cycle is to allow frosy or ice to melt down and not restrict the output air. The thermostat is set too low and in high humidity ice forms quickly restricting the air flow. tur up the thermostat and let the room cool gradually.

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I would suspect you have a problem in the defrost circuit of your heat pump. there are a couple of things you can try. first just run the system on emergency heat and see what happens. you could have a defrost board that is shorting when it kicks into defrost. it sends a signal back to the furnace so it will come on during defrost. if you do not blow a fuse as long as you are running in emergency heat, i would suspect the defrost control board. also you could have a dead short in the wire that runs from the "w" terminal on furnace control board, out to the heat pump. keep in mind that any of the wires could be the cause and i am just tying to give you the most common things. your furnace will still run if you unhook all the low voltage wiring out at the heat pump. if you do this and stop blowing fuses. you know it is something on that wiring. goodl luck.

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Icm 303

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About the only thing I can suggest you check is the initiate termination thermostat (assuming your Heat pump works with one of these). It will be identified by 2 wires going to it and it will be clamped on the line (Not brazed on or screwed on). Now there will also be a reversing valve which has 4 tubes going to it and 2 wires. and it could have high, low, pressure switches that have 2 wires. This thermostat is usually mounted 1/3 to 2/3 way down on the coil and is suppose to be mounted on the "U - Bend" of the out door coil tubing. It usually resembles a pancake and will have a wire or metal clip that holds it securely on the coil U bend. Make sure it hasn't fallen off or come loose. This can cause your heat pump to miss its required defrost.

You can try this also. Some defrost timer boards have a set of "test pins" you put them together with a screwdriver or a piece of wire for a few seconds to initiate a defrost. It defeats the time logic in the board It should go on into defrost and stay in until the coil is cleared of frost and or about 10 minutes which ever comes first. If it comes out right away it may be the termination switch I talked about above. It could also be the board. To check out the thermostat locate the 2 wires going to it from the board. pull them off the board and retry it. Sill goes right out of defrost then jumper the 2 wires together and try it again. If it still comes out this time it most likely the board. If it stays in defrost either time when removing the wires or jumping the wires its the thermostat.

If its anything else; Well Its a little complicated and unless you understand the heat pump /refrigeration cycle and the need for defrost and how the defrost is limited and initiated, well Id say need a pro.

Hope this helps you. If so please rate me as high as you can. Thank you for using fixya and good luck.

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On My goodman heat pump, It had blown the transformer, I installed a 3amp fuse and when engaged into cool mode blows the fuse. I have narrowed it down to the yellow wire in the heat pump that goes to the...

That low pressure switch is isolated so that would not be the issue. The defrost board is the most likely culprit but you did not post the model number to tell more

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