Ohio Carrier 2 Stage 3 Ton Unit - Open Loop, CXM Trouble Code 4 - FP-1 Low Temp Coax (Water Side Freon Be

Discussion in 'Maintenance and Troubleshooting' started by mrrxtech, Feb 22, 2016.

  1. mrrxtech

    mrrxtech Member

    I was looking into a Lock Out of a Carrier 2 Stage, 3 Ton Unit that has an open loop cooling medium, which is experiencing a CXM Trouble Code 4 - FP1 Low Temperature on the Water Side Coax/Heat Exchanger as sensed by a Thermistor located on the outlet of the Thermostatic Expansion Valve (TXV) supplying Freon to the Water Side Coax/Heat Exchanger while in the heating mode.

    The Unit operates fine in the 2 Ton Mode.
    When the thermostat is raised to the 2nd Stage Y2/Aux Heat temperature set point, the 2nd Stage energizes the compressor electromagnet port blocking ring increasing the compressor to 3 Ton operation.
    After the design delay(s) the compressor contactor opens while the whole house fan continues to run.
    The CXM controller as stated above shows an FP1 Fault Code.

    The water temperature into the Unit was at 49 degrees and steady at the time of the trip.
    As a Side Note: Water Supply Header Description, although bypassed temporarily due to issues.

    The system uses a dual water supply header made up of a 3/4 inch Diaphragm Solenoid Valve with downstream throttle for the 2 Ton mode, and a 1/4 inch Diaphragm Solenoid Valve for the additional Ton of Heating/Cooling when Y2 is called for by the thermostat.
    I removed the Y2 thermostat wire from the Unit to prevent 3 Ton operation which allows the Unit to heat the home using the 2 Tons. No trips have been experienced in the 2 Ton mode.

    My plan is to 1) Check the Thermistor using the tables provided by the CXM Controller owners/tech information to see if the resistance is within tolerance. If too far out of tolerance I'll replace the Thermistor which should correct the problem.

    Another Side Note: Water Supply Reliability Improvements Planned
    To make the water supply more reliable, I'm going to replace the Diaphragm Solenoid valves with Taco Sentry Motor Ball Valves on the 1/4 inch an 3/4 inch dual supply header since water conditions are causing the diaphragm valves to clog, reducing flow on the 3/4 inch valve and causing the 1/4 inch valve to leak by after being de-energized.

    Also a strainer/filter on the supply could improve the water conditions, but this will require the owner to "Do Something" at a given frequency, which they oppose since Heating and Cooling should not require any maintenance except changing the Air Filter after several months.

    Using the Wood Burner to heat the home when the Geothermal Heat Pump trip off, results in a lot more time & effort than replacing a water filter "as needed", but these are the folks that Text To Talk, and use a GPS/Tomtom to get home rather than knowing the way home by landmarks and signs. Go Figure!
    ALMOST FORGOT: Any ideas on other possible causes for FP1 Trouble Code, if the Thermistor Resistance Checks out OK?
  2. geoxne

    geoxne Active Member Forum Leader

    Not enough flow in second stage. Failed or clogged valve? System pressure drop?

    The rule of thumb for open loop flow is 1.5 gpm/ton with entering water 50F or greater, otherwise 2gpm/ton. Most manufacturers do not recommend 2 stage flow control for units 3 tons or less. Some times we have to conserve every drop of water especially in a marginally performing water supply system. Your call. I have used Taco Zone Sentrys exclusively over the last 5 years with no problems. I recommend inline flow controls such as Hays or Dole. They react to changes in pressure, something flow setting valves can not do.

    I filter all my open loop systems with a Lakos Twist II Clean #60 mesh. I don't want any crap getting in my systems.

    Edit: I forgot to mention you want to use flow control to keep leaving water 40F or above. Also, pushing 2gpm through a 1/4 pipe is ridiculous.
    Last edited: Feb 22, 2016
  3. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    If all else fails try measuring the refrigerant numbers. Then measure all the other stuff they taught you to measure in tech school.

    You may find your charge is low, so do not mess with the water flow side. I do not care what you want to do with flow. You need to match the flow to the heat transfer needs of the machine. You need to be able to measure that flow. It can be done without opening the system.

    Once you know the flow is good, take the next step.

    One needs to know how a system works, to be able to "see" what is wrong and then make the repairs.

    How old is the unit?

  4. mrrxtech

    mrrxtech Member

    Thanks for the response.

    This is my first response and this area doesn't look like where I should be typing but I will give it a try.

    If I decide to use a closed loop contol/feedback system, I'll take a look at the Hays or Dole flow controls.
    The filter recommendation is also appreciated. I have a whole house water filter that I was considering using. The Lakos filter is probably easier to clean than replacing a cartridge.
    As far as the 1/4" flowpath for the extra ton, I believe a 1/4 inch flowpath at a minimum of 30 psi pressure will fill a gallon jug a few times in a minute. I'll check the calculation later.
    Thanks g.
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    First check your flow and your leaving water temp. 10F delta T (39 F leaving water temp) you should be around 1.5 gallons/ton. That will tell you if you have not enough flow.
    Second, check the FP -1 sensor.

    Then, and only then, I would put gauges on and check the refrigerant.
  6. mrrxtech

    mrrxtech Member

    The Unit was built Dec 2013. It had one bad event in 2014 when the house lost one of its 220 hot leads due to a tree limb blowing onto it and breaking it loose. The 24 vac transformer burned up since it didn't have the built in breaker protection that was shown on the schematic. The new transformer has the breaker.
    Other than that the Unit has run fine, except when a valve gets clogged and the flow drops. It may need a water side flush due to the coating on the tygon hose outlet pipe that is being used to monitor iron & other water carried "things".

    I've worked on my own auto AC system, since the day the repair shop wanted to replace the compressors in a 3 month old vehicle, when nothing was bad except for a small leak. I don't like to use gauges since the Freon leaks out when you hook up or purge the lines of air if needing to add Freon.

    Tech School for HVAC is one school I never attended, but I have been going to schools for a very long time. Heat Transfer & Fluid Flow, Physics, Electricity, Electronics, Nuclear Physics are areas I can draw from to understand how things work. The nuclear part I don't use as much but you won't lose me when applying the E=MC2 formula.

    I saw measurements in the Carrier Unit Check out process that show how flow can be determined by using the Freon Side measurements.

    My Brother and I have Reynolds Number arguments all of the time when discussing my closed loop Geothermal Unit when it can't keep up with the Ohio Cold. He blames everything on a bad Reynolds number. I probably need a back up heat source or add more ground loop to keep the temperature out of the 20s in the loop as we saw in 2014 when everyone had heating problems when using a water source ground loop heat pump.

    Thanks for the reply Mark.
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Not the worst thing if the loop drops down to the mid to the high 20s. Plus a well designed single or dual stage unit should need some supplement heat when designed with economy in mind.
    Reynolds number and closed loop: Before you were discussing an open system? where is the reynolds number and a closed loop now coming from?
    Also, not everyone had heating problems in 2014. It is a simple matter of heat pump capacity and sizing.
  8. geoxne

    geoxne Active Member Forum Leader

    Just in case you misunderstood. Take a look here for geo industry standard open loop flow control-

    The standard test to check flow is to measure the pressure drop across the coax coil with a single gauge through P/T ports on either side and compare to manufacturers pressure drop tables. It is nearly impossible with a standard gauge to accurately measure open loop flow rates when you might be looking for example 0.8 to 1.2 psid. At least seeing a difference will confirm flow. Watch for pressure dropping from the source or pressure rising to the discharge to help aid diagnoses of flow issues. Monitoring LWT and FP1 temps while running will allow you to see what is happening.
    Beware of "cold starts" or deep setbacks (low entering air temp). Under these conditions the heat pump is ripping more btus out of the source water and refrigerant temps and LWT can drop of the cliff.

    Rule out all water flow issues before suspecting low refrigerant charge.

    Filtering not only protects valves and equipment, it protects the discharge (in my case discharge well screen) from clogging.
  9. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Gee, I do not remember saying put on manifold gauges to check the charge.
  10. mrrxtech

    mrrxtech Member

    If all else fails try measuring the refrigerant numbers.

    I took that to mean you would hook up the gauges first to do all of the analysis. I'm sure there are Technicians that live by that, and others that look at all the other parameters first and reserve the freon checks for last. I don't have a history of Freon issues vs loop issues that would cause me to start on the Freon side. For Automobile AC systems it's always the Freon side that has the problem, since the cooling medium is air flow.
  11. mrrxtech

    mrrxtech Member

    I've seen a lot of different devices in more systems than you can imagine, but I've never seen a constant flow control device like the Hays Series Measureflow auto flow control device.

    I could put a 3/4 inch 4 gpm Measureflow device downstream of the 3/4 inch Taco Sentry motor ball valve and a 1/4 inch 2 gpm Measureflow device downstream of the 1/4 Taco valve if I wanted to go with 2 gallons per ton, and use the 2nd stage flow path to carry the 2nd stage 1 Ton.

    This is just a quick example. I'm use to cabinets full of instrumentation to measure and control system flow rates, this device is much simpler.

    I would want to look closer at the flow vs compressor amps to determine the most efficient flow rates before investing in the Hays Measureflow devices.

    I looked at 3 different Twist Flow filters including the ones you mentioned. I think the Campbell with an Automatic flush valve would solve the problem of Silt removal with no requirement for the owner to lift a finger/perform maintenance, like turn flush the filter.
    The #60 mesh appears to be the best size for this type of filtering from what I saw advertised, as you mentioned.
    This was new to me, and I can see how the filter could improve water quality for the whole house as well as keep the Geothermal System cleaner and increase resin life in the water softener.

    The Carrier owners manual has the table for determining flow based on D/P across the coax coil as you discussed.

    Thanks for the dynamic pressure & temperature monitoring tips. This is something I wouldn't have thought look for until after seeing an issue in the coax coil during flow a few times.

    I've had 3 homes with Heat Pumps and never experienced a problem with the Freon side except a gas leak after 13 years. The houses I owned in the South showed no Heat Pump issues before I sold the homes. One Unit was 10 years old and the other a packaged unit that was 5 years old when I headed back up North.
  12. mrrxtech

    mrrxtech Member

    You're right, I was talking about the open loop system that I was working on. The closed loop system is another story.
  13. mrrxtech

    mrrxtech Member

    From my experience with the Split System Heat Pump, when below 30 degree air temperature, it's time to kick in the back up heat source, or the unit will run and defrost continuously.
    It sounds like having water below 30 degrees as a heating medium is less of an issue when using a Water Source Heat Pump. Is that right?

    I'm sure there is some scientific explanation for <30 degree water BTU availability vs <30 degree air BTU availability.
    I've never evaluated this fact but I bet Geothermal Professionals have considered this in Tech School.

    I'd like to see an explanation on this if someone has a good example. I could say I have a feel for it, but I've never had to put together an explanation for a presentation on this topic. I bet someone else has done this.

    Thanks docjenser.
  14. arkie6

    arkie6 Active Member Forum Leader

    The reason an air source heat pump has to periodically run in defrost mode when the outside air temperature is near or below freezing is that moisture in the air freezes to the outside refrigerant coils which are much colder than the air temperature (the refrigerant must be colder than the air temperature to allow it to extract heat from the air). This frost blocks air flow across the coils and insulates them thereby reducing heat transfer from the air to the refrigerant. This is why air source heat pumps must periodically run in reverse with the outside fan off to melt the accumulated frost.

    With a geothermal heat pump that may experience sub-freezing temperatures on the entering water, the water will or should have anti-freeze added to prevent freezing of the loop water. The water source heat pump can extract heat from sub-freezing water just like an air source heat pump can extract heat from sub-freezing air, but the water source heat pump doesn't have to deal with the frost issues so it doesn't have to go into defrost mode.
  15. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The difference is that water source HPs usually have antifreeze, thus the freeze protections usually kicks in at below 15F. Plus when water freezes it goes through the Phase change, a large amount of energy is released, thus the loop usually stabilizes around 30F. Not the case with open systems.

    So water with antifreeze does not freeze at 30F, an air coil with moist air does.

    Arkie, you just beat me while typing....:)
  16. mrrxtech

    mrrxtech Member

    Thanks for the replies Arkie & docjenser, on the Air vs Water cooling medium and Heat Pump defrost details.
    When I was looking for a closed loop antifreeze I found methanol to be the easiest to locate and its relatively cheap in a 55 gallon drum. There is an XL spreadsheet that I found from a school that gives all the details of water vs methanol mixture with resulting freeze protection. I'll attach a copy.

    My Brother used methanol in one of his systems back when he was using closed loops on his Geothermal Systems. He went into a lot of detail to tell me how to inject it into the loop after first partially filling the loop with water. As we all know Methanol is Funny Car fuel and highly flammable.
    I wouldn't use methanol without first mixing it with water by siphoning into drums that are already filled to the proper level with water to give the intended freeze protection mixture when the drum is full. Pressurizing a drum of Methanol to push it into a loop is something I just wouldn't try.

    What do the pros use in their closed loops. I figure an environmentally friendly automobile antifreeze would do the job but be very expensive.
    I read where the antifreeze can reduce the heat transfer capability of a loop if mixed in too high a concentration.

    I'll attach the XL Spreadsheet later, my Microsoft Office is on another computer.

    If you have customers or relatives affected by the Ohio drilling, you might be interested in knowing what I've been working on, and how much money has been stolen from Ohio while our gov & atty gnl stand by doing nothing. They have both come into money since Chesapeake showed up in Ohio.
    That would be on another website not related to Geothermal. I'll post the website if anyone is interested.
  17. mrrxtech

    mrrxtech Member

    Here is the XL Spreadsheet for determining total loop volumes based on pipe size and length, and Methanol Antifreeze mixture based on gallons added.
    Open the various pages by clicking on Page 1, Pipe Volume Calculator, and Physical Data on the tabs at the bottom.

    Attached Files:

  18. geoxne

    geoxne Active Member Forum Leader

    You are on the right path I believe except for 1/4" pipe. If system pressure drops that is the last place the water will want to flow.

    I still believe 1/4" piping for flow up to 2gpm is pushing it. The pipe size becomes the flow restrictor at a given pressure rather than the flow controller.

  19. mrrxtech

    mrrxtech Member

    According to the Hays Flow Recommendations, the 3/4 path is within design but the 1/4 inch could be changed to 1/2 inch to reduce noise.
    Thanks for the information.
    Did the XL Spreadsheet look familiar or helpful for designing geothermal loops?
  20. geoxne

    geoxne Active Member Forum Leader

    Regarding noise on an open loop system-
    Any valve will make noise if there is 8psid across the valve. The Hays Measureflo can make noise especially in higher pressure systems with low or no discharge pressure. I install a ball valve after each flow control path not only for isolation but to adjust back pressure on each circuit. If you are getting a lot of water noise start closing down the valve until noise is acceptable. Double check to make sure you have not effected proper flow. When you find your sweet spot take off the handle.

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