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Help with HVAC?

  1. wilderness profile image96
    wildernessposted 3 years ago

    Saturday my furnace (heat pump) died - the air handler fan won't come on.

    I was able to verify it's getting power, and the motor was hot.  Turning the fan "on" rather than "auto" and spinning it by hand starts it up.  It's been running like that for 2 days now without a problem.  I assume it is the capacitor that is bad.

    Question; parts houses are all closed today.  Am I going to damage the motor this way, running it 24/7 with a bad capacitor?  Do I need to interrupt some service guy's day off (and pay triple in the process) to get a new capacitor on before Xmas?

  2. paradigmsearch profile image90
    paradigmsearchposted 3 years ago

    Don't know if this will help or not...

    My refrigerator fan sometimes doesn't spin when it is supposed to. And the unit is likewise hot.

    I flick the fan blade with my finger, and it starts happily spinning like it is supposed to.

    This has been going on for quite some time.

    Your results may vary.

    1. wilderness profile image96
      wildernessposted 3 years ago in reply to this

      Well, the "quite some time" may mean something!  Thanks, Paradigm.

      I don't think it will hurt a thing, but am not going to keep checking it, either.  Have to open the outside entrance to the crawl space (a large steel plate covering a concreted hole in the ground) and then belly crawl 30' to the unit but still have to open the side of that to do anything.

      1. Marcy Goodfleisch profile image93
        Marcy Goodfleischposted 3 years ago in reply to this

        Check for hubs by Cre8tor - he's an HVAC expert & has written many hubs on maintaining your system yourself.  He's also a super decent guy - you could probably send him a message with your question.

        Good luck!

        1. wilderness profile image96
          wildernessposted 3 years ago in reply to this

          Thanks, Marcy - on my way.

  3. rexbwell profile image60
    rexbwellposted 3 years ago

    It is unlikely that the motor will sustain further damage while running with the bad cap in place. It's when the motor stops as the cap continues to fail that the damage builds up. Be advised that the windings in the motor may already be compromised to the point the it is not salvageable.

    1. wilderness profile image96
      wildernessposted 3 years ago in reply to this

      Thanks, rexbwell.  At this point my plan is to replace the cap and see what happens.  It seems that the motor was stalled for several hours before I caught that it wasn't working, probably overheating and constantly resetting, so it may well be damaged.

      At the same time, the motor has now run for nearly 4 days 24/7 so I do have hopes that it is all right.

      Either way, it's good news that I won't further damage the motor by allowing it to run - the weather is nasty today and I have to crawl around outside to reach the crawl space. I'm not anxious to do that in a snow/sleet storm and will probably wait another day or so.

  4. rexbwell profile image60
    rexbwellposted 3 years ago

    Be advised, a reputable and skilled technician knows that motor can't be guaranteed to continue running. He might decline to warranty the repair or strongly suggest you let him replace the motor. Either way, he's not being shady, he's just trying to protect your best interests while simultaneously protecting the best interests of his employer.

    1. wilderness profile image96
      wildernessposted 3 years ago in reply to this

      Not a problem as I'll do the work myself.  The only reason I had to consider a service call was that I couldn't get a cap before Christmas, while a service truck should have one on board.

      I figure it's 50/50 the motor is shot, even though it's running, so I just need to make sure when I get the cap it's early enough in the day to install it, test the motor and get back to the parts house for another motor before it closes.

      If the worst happens and I lost all heat, I can have the old resistive ceiling heat reconnected in the panel and up and going in less than 30 minutes.  I never cut the wires when the heat pump was installed, although the breaker space was needed, just disconnected them, labeled them and capped them off.

  5. rexbwell profile image60
    rexbwellposted 3 years ago

    When you test the motor, make sure you take your amp reading with the air handler cover in place. If that number is less than the motor's rated RLA after a minute or two of run time, then you might be ok.

    1. wilderness profile image96
      wildernessposted 3 years ago in reply to this

      I never thought of that, but you're entirely correct in that the cover will affect the amperage draw.  Unfortunately, my ammeter doesn't have a "max" feature so I can't do that.

      Wouldn't do any good anyway - the motor is buried inside the squirrel cage and I'd have to pull the fan and take it apart to see the nameplate.  What little paperwork I have on the unit is pathetic and I don't trust anything on it.  The wiring diagram was wrong, as are some of the parts - it's just a generic with a strong hint that things change but paperwork doesn't.

      If I were to go to the effort of pulling the motor, I'd probably just replace it with a new one anyway. It's 10+ years old, can't cost that much and I'd probably be ahead to put in a newer, higher efficiency motor in if I did pull it.

      1. rexbwell profile image60
        rexbwellposted 3 years ago in reply to this

        To take an amp reading, run the fan only and take your reading at the disconnect switch. For reading the motor, an inspection mirror and a mini-maglite used to be enough when my eyes were young. Since the wiring diagram is wrong, is it possible that is a replacement motor already? Also, one, two and three speed motors haven't changed much in efficiency over the years. Efficiency is gained by using variable speed motors, which you can't just simply upgrade to. You'd have to replace the unit. As far as the cost of a replacement  generic like the one in place, look at anywhere from one to three hundred.

        1. readytoescape profile image59
          readytoescapeposted 3 years ago in reply to this

          Just to add: The FLA data for the fan motor should be included on the AHU nameplate. You should see Minimum Ampacity,  Maximum Fuse Size, Full Load amps and Horsepower/Watts/KW (Fan & Heat).
          Even if this is a replacement motor it should be close to those specs. I agree with Rex if the fan is running it is probably undamaged. You can also do a quick calculation to determine a close approximation of what the amps for your motor should be; 1 Horsepower (746 watts) divided by Applied Voltage.

          For example:
          A ¾ HP motor at 230 volts should be 746 x 0.75 / 230 = 2.43 amps

          If your amp reading is within 10% or so of this calculation the motor is running optimally.

          When first starting the motor you will see at least a 25% jump in the amperage then it should settle close to your calculation. This is the starting load and should not exceed the Max Fuse rating. Remember that without the capacitor this may be a slower than normal process and perhaps even higher than your Max fuse. If the amp rating stays high, as Rex said the motor could be damaged.

          1. wilderness profile image96
            wildernessposted 3 years ago in reply to this

            I haven't looked, but you're right that the FLA should be on the nameplate of the AHU.

            Never thought of using the HP/watts figure.

            I've always started with 1 amp / HP for a 480V 3 phase and gone from there.

            Halve the voltage, double the amps so 2 amp/HP for a 230 3 phase, multiply by 1.7 for single phase.

            A 3/4 HP motor at 230 should then need 2.55 amps; pretty close to your figure of 2.43, especially as motors vary in their efficiency and amperage draw. 

            Yeah, the initial surge can be enormous - I've seen motors that need 3 and 4 times the FLA to get started and it seems like the NEC limits the fuse size to 7X the FLA (or more - I'd have to look it up to know for sure).  It's why we use slo-blo fuses and HACR rated breakers - they will tolerate a short term overload while still protecting the motor should the current go too high for longer periods.

        2. wilderness profile image96
          wildernessposted 3 years ago in reply to this

          The disconnect switch is a pair of breakers (30 and 60 amp) built into the air handler - you have to take the cover off to get to the wires.  I could do it in the house panel, though.

          No, it's not a replacement - it was installed since I bought the house.  It's a 3 speed motor (I think - there are too many wires and the paper work says it is) using only one speed - why I can't imagine except maybe to allow for different ducting needs. 

          The mirror and maglite - as you say, it would probably work when I was younger, too!  smile

          I installed a fancy three stage programmable thermostat with outside temperature sensor a few years ago and had trouble deciphering the wiring because it didn't match the diagram.  I can read a diagram but can't look at a physical part and know what it's doing as I don't know HVAC and have only a rudimentary knowledge of how a heat pump works. 

          Finally called customer service at the manufacturer, but when they found out is was just a home owner they wouldn't even talk to me.  Just said call a service man. 

          Disappointing as I was looking for advice on the use of the heat strips.  It had been installed using only 2 of the 3 heat strips and I wondered how to best split them up for auxiliary vs emergency heat, given that our ambient temperature seldom gets down to zero and that I now had a 3 stage stat.  I think I finally chose to use one strip for auxiliary and two for emergency but have no idea if that's the most efficient.

          I also studied the efficiency charts on the heat pump and finally chose to shut down the compressor at 25 degrees ambient, going to heat strips then, but don't know if that's the most efficient, either.  It works, but I don't know if it actually saves money.

          Sure wish companies would publish more information as I've found that most service men can make it work but don't really understand how to give the most efficiency based on the house, temperature inside and out, etc.

          1. readytoescape profile image59
            readytoescapeposted 3 years ago in reply to this

            How we sent Heat pump systems up here is the HP is stage one, Auxiliary is stage two and Emergency is stage three; all of which are controlled by the T-Stat. Programmable stats should have Kick points that tell the different stages when to “kick in.” These points are usually determined by temp range differences and some by a specified run duration differential.
            For example if the unit has been off and the normal heat setting is 68 degrees, should the ambient temperature be 5 degrees low (63), just stage one will kick in. It should run for twenty minutes or so to bring the temp up to the setting. If this is not reached within the specified time limit, stage two kicks in or if the initial start temp is 15 degrees lower than desired (53), both stage one and two kick in at the start. Stage three will kick in the same as stage two or all three will start if the initial temp is 25 to 30 degrees below the normal setting.
            Also variable speed fans are typically tied to these stages, the lowest speed for stage one working upwards, medium for stage two and high for stage three. This is both a safety feature to keep the elements from burning up as well as an efficiency setting to move and heat more air as quickly as possible thereby conserving power.
            The system should also be configured the same way for shut down, using the same temp differentials; stage three off first, then stage two and finally stage one.

            1. wilderness profile image96
              wildernessposted 3 years ago in reply to this

              That's exactly what I wanted to do, just didn't know the set points.  I know the stat is programmed to hold the temp within +- 1 degree normally, but night time settings are -5 degrees and that should kick in the aux but ONLY if the compressor won't do it within a time limit. Or if the outside temperature is under 25 degrees, where the stage one compressor won't come on at all.

              However.  I put in a Homeywell TH8000, and honeywell told me that the stage three is only accessible via the emergency heat button - that it will never come on automatically.  Not sure if I believe them as the guy I talked to didn't seem too knowledgeable, but that's what he said.

              All of those set points are accessible only with the deep programming of the stat done by the installer, so I'm going to have to go further into it than I did in the past to get it right.  I just don't always understand the terminology - it's what happens when an electrician works on HVAC. smile

              The other problem is the motor - what you're saying makes perfect sense, I just don't know how to hook it up properly (or if it can be done at all) in the AHU.  As I recall, some of the motor leads aren't used, which would mean that they need hooked to something - a relay or other control - in the AHU that is either controlling the heat strips or is controlled by the heat strips to vary the motor speed. 

              Again, it's what happens when an electrician tries to do the controls of a heat pump.  It really looks to me like the installer took the easy way out and just made it work without trying to make it work properly.  Or maybe they did the best they could with a cheap stat - I don't know.  I just know that basically I have to trace every connection, figure out what it's doing and how to make it do something else.  Not easy when I don't truly understand the connections between compressor and AHU - the defrost cycle gave me fits, for instance, trying to understand what was going on as the control signal comes from the compressor unit and not the stat.

              1. readytoescape profile image59
                readytoescapeposted 3 years ago in reply to this

                I’m an Electrical guy too, but spent a lot time doing this at Johnson Controls. It’s hard to tell you how to reconfigure (if necessary) without seeing the set up. But a quick look at the Honeywell site seems to indicate (judging from your description) you should be using a TH8320U.

                1. wilderness profile image96
                  wildernessposted 3 years ago in reply to this

                  I'm not sure what model it is - I grabbed the manual to make these posts with and it just says "VisionPro TH8000 series". 

                  I suppose it's stamped inside the stat, but I'd have to pull the cover to see, which would kill the AHU blower and it won't start again without me going under the house and spinning it up by hand.  Not gonna do that! smile

                  Judging by what I see in the manual, I think that's the model, though - TH8320U.  The 10U is a single stage (I think) and the 21U is for dehumidifiers, which I don't have. 

                  I've done lots of control work and understand controls in general, but in an industrial setting, not HVAC.  I remember seeing a large multi-pole relay in the AHU, for instance, but don't know what it's doing or even how many poles it has or what's turning it on.  I also remember seeing the heat strip terminations and thinking they were some kind of sensor - it took a bit to figure out they were the heating strips.  smile

                  I realize that you can't give specifics without actually seeing the unit, but I sure appreciate your help.  You've given me some ideas on what to look for and what might be possible - more than either honeywell OR the heat pump manufacturer ever did.  I couldn't get much from the one service call I've had as he wasn't a control expert and talking to HVAC guys on the construction jobs didn't help as they don't do residential. 

                  It all works and keeps us warm and cool, I just think it could work more efficiently than it is.