I have old GE furnace (gas/central model 21LU105D2M1) with 2-speed blower fan (blue,red & white wires)
Heating work good, low speed first & after warm up high speed.
Problem is with A/C. Seems like its work always on low speed.
On low speed air flow is to weak to cool down 2nd (top) floor.
I drow schematic diagram, so will be posible to understand what I did.
I took out red wire (from #4) and insolate, then I took out blue wire (from #2) & connect to #4.
Turn on switch & nothing happen.
Then I connect everything how use to be and it still work (only low speed).
What can I do to make blower motor work on hi speed with my old FEDDERS A/C?
Any ideas? HELP, PLEASE!!

There is a relay setup on your unit. The motor is connected to it. When in cool mode the green low voltage wire sends a signal to the relay to run the motor at high speed. It is possible this relay is defective but test before replacing.

I check relay and is good.
Any other ideas guys??
Is this possible to make that system work only on high speed (just for A/C)?
There is getting really hot upstairs. Tx.

NOTE!!! The wiring on your thermostat is not standard and it is possible a problem exists there. Usually the red R terminal on the thermostat is fed with 24 volts for power. In your case that is not true since you are feeding the R terminal with the W for the gas valve. It looks like the R and W terminals have been reversed and that could also cause the problem you are having.

If the relay was good it would be pulling in and activating the motor blue wire on 2 of relay to the blue wire relay feed on 5. The number 5 terminal is fed back to the power source by a blue wire to the black power wire.

To temporary it on just jump together 2 and 5 on the switch BUT for safety sake I would remove and TAPE the red wire on number 4 terminal on the relay. This should bring on the motor to the highest speed you are showing. It will allow you to test for more air movement but still has not perminently solved the problem.

Now with all that said the relay must not be working. The blue and green that feed the relay coil should have 24 volts on it when activated in the A/C mode. Then when the 24 volts are there the relay should activate and close the relay between terminals 2 and 5. This will put the motor into the high speed range. Retest the relay since it has to be bad and not activating the 2 to 5 terminals.


Now red is low speed and usually blue is medium speed on most motors so it seems there is no true high speed motor leed to start with. See attached diagrams.

On almost all standard thermostats this is the wiring setup.

Red= transformer
Yellow= contactor
Green= fan
white=heat