Waiting to startup-what is this sensor in my Climatemaster?

Discussion in 'General Discussions' started by Dale, Feb 14, 2008.

  1. Dale

    Dale New Member

    Here in Texas, my system has a payback of 2.5 years and an ROI of 30%. The cost of natural gas and electricity tend to go up in unison down here because 70% of Texas electricity is generated with natural gas boilers. We have seen pretty serious increases in both the past couple of years. The cost of fuel oil certainly makes a good case for geothermal but, at least in Texas, the cost of natural gas and electricity make a compelling story as well.
  2. stevecaz

    stevecaz Member

    3 weeks ago I started my 3-ton Carrier GT-PX (a climatemaster tranquility 27 unit). All work was done by me except for sheet metal duct connection, and its been working perfect (write-up coming).

    But for my other 2-ton split unit, the duct work, refrigerant lines, and charging was just done, but I have this purple wired sensor zip-tied in the unit clearly there to be connected afterwards - but there is zero about it in the manual. It looks like a temp sensor (thermistor) and comes with a clip to attach it to a pipe, and based on the clip its for a 3/8" pipe like the liquid line. Then it has two bare ends that look like they are suppose to push into a molex wire harness (and there are two open spots in the molex harness on the CXM board both labeled "CO". This is the only place I can see these going.

    I don't want to begin startup without having this in place.

    Edit - ok I realized its the FP2 sensor, and I also pulled back on the molex harness wires to find the FP2 spots are just jumped together with a purple wire. So do I remove the jump, insert the thermistor connectors, and clip the sensor to where?
  3. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    It has been awhile since

    I have had my head inside that unit. Purple is the FP2 sensor harness. I looked at my copy of the engineering manual for the CXM board, (I can send you a copy) and there is nothing showing the exact location of the sensor.
  4. stevecaz

    stevecaz Member

    Well given the sensor is included for connection after installation, and that its not already installed, that sort of indicates it should be connected to the new 3/8" liquid line that was brought into the unit and brazed to the connection near the valves.
  5. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    My bad

    I missed that this was a split. I don't have an I/O manual for any splits, but I think you are correct as to location. My guess the jumper was for out the door testing.

    I am surprised a field installed sensor in not mentioned in the I/O manual.
  6. stevecaz

    stevecaz Member

    OK, I luckily found this described on a chart inside the flip down cover that goes over the CXM board. I had extra literature stored on top if it. But I am a little puzzled why they couldn't include this diagram in the manual. And by the way, my Carrier dealer had no idea of where it went.

    So it says I cut the violet wire that is jumping the two FP2 spots on the molex harness, then splice into that with a wire leading to the fan coil, and to place the sensor "on copper tube between distributor and expansion valve". Oddly the included pipe clips for the sensor are for smaller liquid lines but I'm hearing its the suction line. Page 18 of the manual does show an un-named sensor bulb placed on the 3/4" suction line just after it leaves the cabinet. However, this is not between the distributor and expansion valve, which is inside the cabinet at the 3/8" liquid line connection.

    I should take some pictures.
  7. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Do take the pics

    The guys that made that board are very good. They sold it to folks that have folks putting together machines who can be clueless. I had an FP2 tightly dangling from a wire tie. At least it gave me a clue what the CXM board guys wanted to monitor.
  8. stevecaz

    stevecaz Member

    Just to follow-up, I placed the sensor on the outgoing 3/4" suction line exactly as the diagram in the manual shows a sensor bulb going (but which contradicts their own description and provided sensor clips). I then started the unit and something wasn't right. But I found the dealer who installed the air handler didn't bother to correct the easy set jumpers to specify a heat pump connection (and not AC), the heat pump type, the connected compressor size. After I set those correctly it has been working well.
  9. Limited, specific comment


    I have access to the Carrier Installation, Operation and Maintenance Instructions October 2010 pdf information and my own hvac experience. I had had cold weather trip out issues on my Carrier two ton version of what you have. (They are posted elsewhere).

    According to Carrier's pdf Fp1 (GREY COLOR on 2 ton unit) is designed to measure temperature and protect the water coil from freezing mainly in heating mode. It is fastened to a portion of the thermostatic expansion valve just before the valve meters refrigerant into the evaporator coil. The engineers believe that this location is the most accurate measurement or indication of what is happening in the coil itself. It allows for fast response, particularly if you have a refrigerant leak, or loss of water flow.

    On my 2 ton unit it triggers lockout code # 4 (4 flashes) at 30 degrees F which is: water coil low temperature. A freezing temperature is IGNORED for 120 seconds only, then it says to the board" open the contactor 24 volt ac circuit and stop the compressor. This keeps from freezing the coil and preventing very expensive damage.

    Since I KNOW that GREY WIRES are the FP1 sensor on the two ton version, (I had to replace the sensor for reading too high), FP2 is probably pink or a different color. So the pink wire thermistor should be the one that measures air coil temperature.

    Change gears. FP2 ( I think it is pink on my 2 ton unit) monitors air coil temperature somehow. I believe it is a 10,000 ohm resistor. It may be mounted on the same thermostatic expansion valve. As I write this I can't remember where it is placed.

    If you haven't carelessly removed things without marking their locations, it should be clear to you. It detects and measures temperatures. If it "reads" the evaporator air coil temperature as below the selected low temperature limit setting for 30 continuous settings it will register a fault. But it will be ignored for the very first 120 seconds of the compressor cycle. Fp2 lockout code = 5 flashes

    A word of WARNING. On mine the sensor leads that go into the bigger plug in clip with numerous wires, (around 8)? can be replaced easily if you are patient and gently pry against the detents of the leads with a jewelers screwdriver. DON'T BREAK THINGS !!
    I accidently broke the lock in plastic piece that keeps the multwire connector locked into place but it does not affect the operation of the unit.

    Always shut off the high voltage disconnect first uness you want to become unhappy, spend a lot of money, or want things to become exciting.

Share This Page