VS Fan

[Needingadvice]

Hi everyone. I had a question on how a vs fan was suppose to work. Does it usually run at a lower speed, unless it needs to get up to a higher temp fast and kicks in at that time? Thanks.

[motoguy128]

VS fans on residential equipment come in two flavors. The first is a multispeed fan that has a constant torque, so the airflow will change a little with ductwork restriction and as the filter gets dirty, but it's still not a fixed pseed like a basic PSC motor. IT's more energy efficient and gives you roguhtly a 1 SEER boost. You also oftne have a low speed fan option. SO when you select "fan" from the thermostat, it rusn at about 50% airflow speed.

The other type is a true vairable speed. IT adjusts the RPM of the motor to match the selected airflow. The airflow is selected on hte control board of the furnace or airhandler, or soemtiems from and advanced communicating thermostat. WHen you select "Fan" it runs at 50% of the cooling airflow, or with an advanced thermsotat the speed may be selectible down to 30%. These motors also usually have logic in the controller so it can be slowed ot better dehumidify either on demand or based on preset timers.

[motoguy128]

Hi everyone. I had a question on how a vs fan was suppose to work. Does it usually run at a lower speed, unless it needs to get up to a higher temp fast and kicks in at that time? Thanks.

To answer your question directly... it depends on how it was wired or set-up. Do you have the fna set to "on" at the thermostat? If so, then it might run at a low speed all the time, then increase when there's a call for heating or cooling. But as mentieond, it depnds on the make model and how it was installed/set-up.

[Needingadvice]

Thanks for the answer, that makes more sense now. That being said, should my Lennox XC13 A/C run at a high speed only, or is that also monitored by the thermostat like it regulates the furnace, as after I had my a/c installed on Wednesday, and when they tested it seemed to run with the fan on high unlike the furnace that regulates the speed between fast and slow depending on heating/cooling needs?

[beenthere]

Post the model number of the air handler or furnace.

[Needingadvice]

Hope this helps. It's also a tempstar.

[motoguy128]

Thanks for the answer, that makes more sense now. That being said, should my Lennox XC13 A/C run at a high speed only, or is that also monitored by the thermostat like it regulates the furnace, as after I had my a/c installed on Wednesday, and when they tested it seemed to run with the fan on high unlike the furnace that regulates the speed between fast and slow depending on heating/cooling needs?


The airflow for heating is usually lower than cooling. What model AC do yu have? If its' a 3 ton AC, the airflow should be 1200CFM. While in heating the airflows on a 60k BTU furnace might be only 600 CFM on low stage and 1000CFM on high stage. I didn't check if that was a modulating furnace. IF it is, the airlfow on the lowest heating stage is closer to 500CFM, so very low.

From teh factory, all furnaces are set to normal rated airflwo. SO in your case, 1200CFM if hte default setting. IF you have a smaller AC unit, the installer has to select the correct airflow using disp switches on the board.

[Needingadvice]

It is a 2 ton unit. To be honest, I'm not really bothered by the extra air flow, it isn't really loud or anything. I was just wondering if it was normal to run faster than the furnace. Sounds like it is, so I'm not going to worry to much about it. Wish there was a way I could check myself what it was set at.

[beenthere]

Tonight, set your stat to heat, and set the temp 10 degrees above room temp. See if its loud when it goes to second stage. If not, then they left the blower set to 3 tons when they installed it.

[Needingadvice]

I checked the furnace this morning with a similar test and it roared into action to get caught up with the temp I picked which was 8 degrees different, once I pushed run program again it settle down to quiet. Now should the ac work this same way or does the ac need to blow hard as its different?

[beenthere]

You have a single stage A/C so it shouldn't work the same way, per say.

Doubtful they set up your blower at all. It sounds like they left everything at factory default.

call them to come and set it up properly.

[Needingadvice]

Thank you so much beenthere, you have been a huge help! I'll give them a call Monday!