Blower works on "heat," but not on "A/C."

[vegashottie]

This is a Rheem 3-ton unit. The IBM works fine with the heater running, but doesn't run with the A/C. Everything else is working fine. No other symptoms. Any suggestions?

It's VERY "hot" here in Las Vegas. Some areas have recorded 122 degrees this week.

[mattison]

Pull the stat from the wall and jump R+G and see if the indoor blower comes on. If it does the stat is bad if it don't your hoing to have to get into the airhandler and do some testing.

[vegashottie]

Thanks. Jumped R+G and the blower does not come on. What might this indicate? And why does the blower work with the heater and not the a/c?

Thanks again.

[hiltontech]

Check your t-stat wires going to the ac, could be lose or cut.

[vegashottie]

Thank you. I will check the wiring from the tstat to the unit. Would this account for the blower working with the heater, but not the a/c?

I will reply with the wiring check results as well.

[hiltontech]

I assume you don't have a heat pump unit, if not then yes it would account why your unit won't come on outside.

[vegashottie]

Thanks again for the response. No, there's no heat pump. I have two Rheem heat/ac units on the roof. The larger unit (the one in question) is for downstairs, and the smaller unit is for the upstairs.

Maybe I'm using the wrong terms and not clearly explaining how the unit is currently working. Everything turns on like it's supposed to, with the exception of the IBM when the a/c comes on. However, the IBM works fine when the heat comes on. I'm puzzled why the IBM works on heat and not a/c? Why would it work with one and not the other?

[Ed Imeduc]

Check the wire schematic on the unit Id say you have lost the blower relay for AC or the high speed on that fan motor is bad.

ED :thinker:

[vegashottie]

Thanks Ed. I have the schematic here in front of me. What should I be looking for? It looks like the Blower Relay is between the Junction Blower Box (followed by the IBM) and the Fan Cycle Control. Does this tell us anything?

If it is the BR, is that an expensive part, and where can I find one? I really appreciate the help.