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  • 3 amp fuse keeps blowing

    Ok so I tried to install a new thermostat, not that big of a deal, done it before) turned it on and nothing (not sure if it worked before because this is a new rent house I just moved into) Started to look at the code(led blinking light) and it said secondary voltage was the problem, I ppulled the 3 amp fuse and it was blown, cool I thought, I found the problem, this from a plumber(yea I know I should stick to what I know best) I replace the fuse with a 5 amp instead, turned it back on and blew it, I disconnected the red and white from the condensoe and tried it again with a new fuse, as soon as I pushed the door safety latch in it immediatlety blew(I saw it light up), My guess is that I have a short in the thermostat wire somewhere. Reason I think this is I feel someone has messed with it before because there is NO SLACK to pull the wires out of the wall, there is only about an inch of 5 wire that will come out of the wall. Is there a way to tell if there is a short in the T-stat wire and is there other things I should be looking for? Like maybe the 24V transformer, I was almost ruling that out because the furnace is only about 2-3 years old, Any help would be greatly appreciated, Thanks
    I don't bite my finger nails, I KNOW when payday is, and yes, it can run uphill when it gets blocked(or you install a grinder pump) so HA!!!!

  • #2
    Re: 3 amp fuse keeps blowing

    The 3amp fuse protects the transformer and the circuit board. If the transformer was gone you wouldn't be blowing fuses. Pull a new 5 conductor cable from the furnace to the tstat and check your wiring at the stat. Might be two conductors touching,causing a short circuit or someone has monkeyed with it before. Check all the wiring to the circuit board with the wiring diagram.

    James

    Comment


    • #3
      Re: 3 amp fuse keeps blowing

      Originally posted by James P View Post
      The 3amp fuse protects the transformer and the circuit board. If the transformer was gone you wouldn't be blowing fuses. Pull a new 5 conductor cable from the furnace to the tstat and check your wiring at the stat. Might be two conductors touching,causing a short circuit or someone has monkeyed with it before. Check all the wiring to the circuit board with the wiring diagram.

      James
      Now that you mention that, there should not be ANY continuity on any of the terminals at the T-stat should there? I mean from one terminal to the next? I already checked all the wires from the schematic on the door and it all looks to be in order also.
      Last edited by PLUMBER01; 09-03-2010, 10:51 PM.
      I don't bite my finger nails, I KNOW when payday is, and yes, it can run uphill when it gets blocked(or you install a grinder pump) so HA!!!!

      Comment


      • #4
        Re: 3 amp fuse keeps blowing

        Originally posted by James P View Post
        The 3amp fuse protects the transformer and the circuit board. If the transformer was gone you wouldn't be blowing fuses. Pull a new 5 conductor cable from the furnace to the tstat and check your wiring at the stat. Might be two conductors touching,causing a short circuit or someone has monkeyed with it before. Check all the wiring to the circuit board with the wiring diagram.

        James
        Agreed

        Comment


        • #5
          Re: 3 amp fuse keeps blowing

          You might want to try disconnecting the tstat wires at the circuit board just make a note of where they go and then put the door back on if the fuse holds then replace wire, hopes this helps you

          Comment


          • #6
            Re: 3 amp fuse keeps blowing

            12 BLOWER ON AFTER POWER UP (115V or 24V) - Blower runs for 90 seconds, if unit
            is powered up during a call for heat (R-W closed). This is what it said when I first put the door engaging the saftey latch to the unit, the blower comes right on, then after about 90 secs it shuts off then the inducer motor comes on followed by the ignition coil(the gas valve does not come on) causing it to reset then start that process all over again, just for the heck of it i turned the t-stat onto cool(with fan on auto) and it isnow giving me a code of secondary low voltage problem and I think the fuse blew again.....wht is the next step?
            I don't bite my finger nails, I KNOW when payday is, and yes, it can run uphill when it gets blocked(or you install a grinder pump) so HA!!!!

            Comment


            • #7
              Re: 3 amp fuse keeps blowing

              Someone correct me if I'm wrong here...

              If you ran a new thermostat wire, and hooked the wires up correctly, I don't think it's an electrical issue, if the fuse didn't blow this time.

              To me it sounds like it could either be a pressure switch or roll out switch.

              The unit has to go through it's safety checks before the gas valve comes on.

              By chance..is this a GOODMAN unit?

              Comment


              • #8
                Re: 3 amp fuse keeps blowing

                Just checked, fuse was blown again, It is a Carrier Model#58STA070-----13112
                Serial # 4109A14384
                I don't bite my finger nails, I KNOW when payday is, and yes, it can run uphill when it gets blocked(or you install a grinder pump) so HA!!!!

                Comment


                • #9
                  Re: 3 amp fuse keeps blowing

                  So all this started when you tried to install a new thermostat?

                  All was working fine before this endeavor?

                  Is there a second thermostat in the house for another piece of HVAC equipment? You may have a 2 transformer system and just need to remove a jumper on the new thermostat and possibly change some settings depending on the stat.

                  Comment


                  • #10
                    Re: 3 amp fuse keeps blowing

                    Originally posted by plumberscrack View Post
                    So all this started when you tried to install a new thermostat?

                    All was working fine before this endeavor?

                    Is there a second thermostat in the house for another piece of HVAC equipment? You may have a 2 transformer system and just need to remove a jumper on the new thermostat and possibly change some settings depending on the stat.
                    Not sure if it worked before, I just moved into this house and the old t-sat was off the wall and the "NEW" digital honeywell the landlord gave me did not come out of a box just a plastic grocery back(maybe they are cutting back on packaging costs ha ha ha)
                    I don't bite my finger nails, I KNOW when payday is, and yes, it can run uphill when it gets blocked(or you install a grinder pump) so HA!!!!

                    Comment


                    • #11
                      Re: 3 amp fuse keeps blowing

                      Originally posted by PLUMBER01 View Post
                      Not sure if it worked before, I just moved into this house and the old t-sat was off the wall and the "NEW" digital honeywell the landlord gave me did not come out of a box just a plastic grocery back(maybe they are cutting back on packaging costs ha ha ha)
                      Honeywell, there's your problem.

                      If the fuse is blowing when you set the system switch to cool you are narrowing down the cause. You stated you disconnected the leads to the condensing unit coil. Did you disconnect them at the furnace control board or at the outside unit? If you disconnected them at the outside unit the leads are probably bare and touching somewhere between the furnace and outdoor unit.When you energize the contactor coil for the outside unit, there goes the fuse. Mice or a whacky weedeater operator are usually the culprits.

                      James

                      Comment


                      • #12
                        Re: 3 amp fuse keeps blowing

                        I disconnected the red and white going to the condensor from the circut board James
                        I don't bite my finger nails, I KNOW when payday is, and yes, it can run uphill when it gets blocked(or you install a grinder pump) so HA!!!!

                        Comment


                        • #13
                          Re: 3 amp fuse keeps blowing

                          ok at the t-stat take the red wire and yellow wire and connect the two does it still blow the fuse red is incoming voltage from 24 v transformer yellow is call for ac

                          Comment


                          • #14
                            Re: 3 amp fuse keeps blowing

                            If you are still blowing the fuse after checking red to yellow.
                            you most likely have a short write down where each wire from the tstat goes on the board disconnect each line and cap them off go back to your tstat and do the same. Start with one color, say red, ohm out each line to red if no resitance your good if you show a resistance it is bad. continue with this till you have covered all combinations.

                            Comment


                            • #15
                              Re: 3 amp fuse keeps blowing

                              Originally posted by kshvactech View Post
                              If you are still blowing the fuse after checking red to yellow.
                              you most likely have a short write down where each wire from the tstat goes on the board disconnect each line and cap them off go back to your tstat and do the same. Start with one color, say red, ohm out each line to red if no resitance your good if you show a resistance it is bad. continue with this till you have covered all combinations.
                              I just replaced the T-stat wire today before the fuse blew again, but I will do the test from you first post thanks, the last T-stat wire had only about an inch of play coming out of the wall in the first place, now I have about three feet to play with.
                              I don't bite my finger nails, I KNOW when payday is, and yes, it can run uphill when it gets blocked(or you install a grinder pump) so HA!!!!

                              Comment

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