Blower wont turn on in "on" mode but works in "auto" with either heat or cool

[CaveGimp]

I have a Carrier F4VC unit and the other day we wanted to turn on just the fan blower to move air around. At the thermostat I changed the fan mode from auto to on and nothing happened. I adjusted the desired temp a bit, and everything kicked on. I check the wires, I have 24v from R to C. I jumped R to G and verified there was 24v and still no fan turning on.

Any suggestions on what to look for next?

 

[Fitter30]

At subbase auto on switch might be bad flip it back and forth a few times
G to C fan switch on 24 vac
R to G if made 0 vac across terminals
R to G not made 24vac
In cooling either auto or on G has power on it to energize the blower relay fan speed high

 

[Sponsor]

 

[WorthFlorida]

What model of thermostat? Is it in heat or cool mode? Heat pump or not? type of heating? It's the thermostat that controls the fan, however, in heat mode and you have gas, the fan control may be on the air handler since gas will preheat the plenum before turning in the fan. Usually the fan in on mode should always operate the fan, therefore look at a dip switch option in the air handler? Some thermostats, usually smart ones, will have an option for the fan operation, either thermostat or the equipment. This is for a Honeywell T-6, # 230. Taking the 24v ac directly to the G lead indicates the fan is controlled by the equipment.

This is the installation manual for the air handler. There doesn't seem to be anything but a normal air handler. There is a "Fan Coil (control)" board but no other information on it.
Installation InstructionsCarrierhttps://www.carrier.com › commercial › media

 

[Fitter30]

Fan control normally is in the furnace blower compartment.

 

[Fitter30]

Look at pages 10 & 11 look at 11 first left side" F" Might have to cycle ahu power after dip switch change

https://www.google.com/url?q=https://resource.carrierenterprise.com/is/content/Watscocom/carrier_fv4cnf005l00_article_1391689348606_en_ii&sa=U&ved=2ahUKEwjhuI2I6bH-AhUpkYkEHXrBDSoQFnoECAsQAg&usg=AOvVaw2GBhkn8DQBfgB27RZ5UYkM

 

[CaveGimp]

Look at pages 10 & 11 look at 11 first left side" F" Might have to cycle ahu power after dip switch change

https://www.google.com/url?q=https://resource.carrierenterprise.com/is/content/Watscocom/carrier_fv4cnf005l00_article_1391689348606_en_ii&sa=U&ved=2ahUKEwjhuI2I6bH-AhUpkYkEHXrBDSoQFnoECAsQAg&usg=AOvVaw2GBhkn8DQBfgB27RZ5UYkM

Thank you for the link, I did find the paper copy when I was in my attic next to the unit but the digital copy is much better.

On line E the jumper is set to 30/90 so a 30 sec delay to fan on and a 90 sec delay to off.
Line F is set to Low.

I tested the continuity of the G wire from the thermostat wall plate all the way to the unit and it is good.

I jumped from G to R (to send 24v to G) and after 1 minute now fan. Also using the thermostat and setting the fan to ON no fan. When I set the desired temp lower to kick on the AC I can hear the heat pump turn on and then 30 seconds later the fan kicks on.

The issue is I can command the fan ON unless the heat pump is either cooling or heating.

 

[CaveGimp]

What model of thermostat? Is it in heat or cool mode? Heat pump or not? type of heating? It's the thermostat that controls the fan, however, in heat mode and you have gas, the fan control may be on the air handler since gas will preheat the plenum before turning in the fan. Usually the fan in on mode should always operate the fan, therefore look at a dip switch option in the air handler? Some thermostats, usually smart ones, will have an option for the fan operation, either thermostat or the equipment. This is for a Honeywell T-6, # 230.

Thank you for the info.

I have an ecobee thermostat with a heat pump and all electric. I believe it is a Carrier 25HCB6.

The fan works when the heat pump is operational, either cool or heat. The fan doesn't turn on when the thermostat is set to continuous but the heat pump isn't running. This is true on the thermostat whether in cool, heat, or off mode. The thermostat reports the fan is running but it is not.

I jumped R to G directly with the thermostat off and still no fan.

 

[Fitter30]

On the board with stat set to fan on. G to C 24vac call for fan. No power. R to G
0 vac.
Bottom switch turn all switches off turn o-o on cycle power that takes all timing the timing out. Wait up to five minutes if there's a timer for power.