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2nd floor AC unit doesn't blow as hard as 1st floor question

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  • 2nd floor AC unit doesn't blow as hard as 1st floor question

    When our house was built in 2005, we upgraded the heating/cooling system from baseboard to hydro forced hot air. We did this because we also installed central AC at the time. Our house has two zones, one upstairs and one for the 1st floor. The other day when it was really hot out, we turned it on both zones. The 1st floor unit blew pretty hard (you could feel it for a few feet away from the vents), while the second floor seemed to be on a very low setting. You couldn't feel the air coming out unless you put your hands directly over the vent. We had the second floor fan motor replaced a few years back. It seems to run fine and doesn't make any strange noises, so I'm wondering if it was intentionally set to come out this way or if I have a problem again. The air is ice cold so I don't have a problem there. I figured I'm get some advice to see if its necessary to call the repair man.

  • #2
    Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

    The air handler fan on the second floor unit may have been set on a lower speed when it was replaced. You should have it checked to see if it is wired for the proper speed.

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    • #3
      Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

      Thanks. I'll have someone come out and make it was installed correctly

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      • #4
        Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

        I'm confused, I'm reading this as the OP has 1 A/C system, with 2 thermostats.

        I see nothing that says 2 HVAC Units.

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        • #5
          Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

          Originally posted by Flux View Post
          I'm confused, I'm reading this as the OP has 1 A/C system, with 2 thermostats.

          I see nothing that says 2 HVAC Units.
          He mentioned replacing a second floor fan motor so I'm thinking 2 fan coils rather than a 2 damper duct system. It's not clear though.

          You want the fan speed lower when using the hydronic coil during heating season. Too high and it'll just blow cool air. You may need to change fan speed settings during the summer months or find a comfortable middle setting.

          If the fan speed is set too low the coil will ice over and block air flow as well. Check for a clogged filter in the unit AND see if there's a return grill filter. Sometimes those are overlooked if the unit was installed in an attic.

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          • #6
            Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

            Is it possible to switch wires on tha fan to make it blow hard in the summer and wire in a rheostat so it can be adjusted for winter? This would keep him from having to change wires to the fan every year?

            I'm no a.c guy but like to guess.lol

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            • #7
              Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

              Thanks for the replies. I'm sorry I wasn't very clear. I don't know much about HVAC. I'll explain our system the best I can. We have two separate sets of duct work. Our first floor ductwork is in the basement and the second floor duct work is in the attic. We have two airhandlers, one in the basment and one in the attic. We have two ac units outside and two separate thermastats one for each floor.
              Basically each zone operates independently of each other. The furnace in the basement pipes heated water separately to either the hot water tank in the basement, the first floor airhandler or to the second floor unit.

              It sound like the person who installed the replacement fan in the attic unit set it to low speed. Is it possible for my fan to have two settings one for AC and one for heat?

              Also regarding the grill filter, where would I look for that? I usually just change the air filters in both air handlers every 3 months.

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              • #8
                Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

                Originally posted by Den69RS96 View Post
                Thanks for the replies. I'm sorry I wasn't very clear. I don't know much about HVAC. I'll explain our system the best I can. We have two separate sets of duct work. Our first floor ductwork is in the basement and the second floor duct work is in the attic. We have two airhandlers, one in the basment and one in the attic. We have two ac units outside and two separate thermastats one for each floor.
                Basically each zone operates independently of each other. The furnace in the basement pipes heated water separately to either the hot water tank in the basement, the first floor airhandler or to the second floor unit.

                It sound like the person who installed the replacement fan in the attic unit set it to low speed. Is it possible for my fan to have two settings one for AC and one for heat?

                Also regarding the grill filter, where would I look for that? I usually just change the air filters in both air handlers every 3 months
                .
                Impossible to say without knowing what air handler, fan motor, control board and thermostat you have in that second floor unit.

                It's good that you change filters every three months. A lot of people don't, including myself. The filter grill will look just like a large return register usually mounted up high in the second floor cieling. It has a couple of latches that open it to access the filter. Some HVAC guys install them there so you don't have to climb in the attic to change filters.

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                • #9
                  Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

                  Originally posted by Den69RS96 View Post
                  It sound like the person who installed the replacement fan in the attic unit set it to low speed. Is it possible for my fan to have two settings one for AC and one for heat?
                  Yes, It's possible. Depends greatly on the unit. but the majority of the units in the area I work in have a high speed setting for the AC and a medium or low speed for the heat.
                  No, it's not rocket science, it's plumbing and unlike rocket science it requires a license.

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                  • #10
                    Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

                    If you have a wiring diagram for your unit, and if it has this feature, it will have several "unused" multi colored wires coming off of the motor. Each wire will make the fan run at a different speed. The wiring diagram will tell you which wire does what speed. There will be a cool and a heat spade terminal that these wires will plug into. (at least this has been my experience on the couple of units I have worked on)
                    We don't have preventative maintenance around here, we have CRISIS MANAGEMENT!

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                    • #11
                      Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

                      Thanks for the info. I think the next time I have my service co here, I'll have them check the wiring etc. At least I have an idea as to what to have him look for.

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                      • #12
                        Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

                        I think you may have a zone dampner not opening, from what you have explained anyway. The unit is sending the correct volume of air to fill the needs of both first and second floors (assuming it was sized correctly), however the zone dampner for the first floor is operating correctly, opening as far as it should, but the second floor zone dampner is not opening up enough, if at all causing all the air designated for both floors to be sent to the top floor. Have someone turn off both zones, then go to the location of the zone dampners (in the duct very close to the supply air dutwork at the unit). Turn on the first floor zone and note airflow. Then turn on the second floor zone. If you are at the zone dampners during this time, you should hear the motorized dampners open up. If the first floor zone opens up and airflow seems normal, but drops as the seond floor zone is turned on, your system is undersized. Also see if the zone for first floor closes as the second floor calls for a/c. Hope this helps, lemme know the results.

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                        • #13
                          Re: 2nd floor AC unit doesn't blow as hard as 1st floor question

                          thanks I'll check out the dampers as well. I don't think its related to the first floor as the ductwork is not connected. The second floor has its own separate ductwork in the attic and the first floor is in the basement.

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