# A/C Question: Just replaced Fan Control Unit and now the Blower false starts cooling



## redmachodevil (Aug 10, 2008)

A/C Question: Just replaced Fan Control Unit and now the Blower false starts every time the Cooling goes on
I had an HH84AA009 in my carrier air handler. This air handler does both cooling and heating. A few days ago, the blower stopped turning off and remained constantly in the "on" position (even after moving the switches on the thermostat to "off" and Auto)

When I'd power off my system and open the unit, If I tapped the relay with a screw driver the fan would turnitself off, however once it went on again it wouldn't turn off.


I replaced the unit with a new ICM275. I replaced wire for wire one at a time, so I am pretty sure that I did it correctly.

Now, the fan works well, however when you put the unit into cooling mode, the blower will go on, and then as soon as the cooling kicks in, the unit kind of "resets" the blower turns off and then tries many consecutive "false starts"


Have I done anything wrong?

Is this newer controler board (with new kind of relays) different and therefore I need to change the wire connections

The new replacement board is different than the original one. The old one has the big old style relays while the new one has the newer relays. This new Board (ICM275) is the currently availible replacement for many legacy Carrier boards including the HH84AA009 (which is the one I had). The board has the same form factor and all of the connection terminals are labeled exactly the same as in the old board. As mentioned before, I connected the wires from the old to the new one at a time to make sure I got them right.....

There is a delay feature that can be adjusted by moving a potentiometer dial.

Maybe somewhere out there knows if these newer boards (that use SPST-NO blower relay, SPDT blower speed relay and SPST-NO relay for humidifier) require any wiring changes from the old boards (that use SPST-NC or DPST-NC heating fan relay and DPDT cooling fan relay 2f)

THe board is made by ICM controls and the schematics are on the icm site.

it seems that when I set the blower settings at the stat to "on" instead of "auto" both the cooling and blower work. When I change the setting to auto, I get the problems again

Any a/c tech that has to repair these carrier units has no choice today but to put in this newer icm275 board, so it must be a common issue, I also supect that relays now function differently.
Here is a quote from the manual, however I don't understand it enough to know what to modify:

"Operational Differences and Added Features
The following is a description of the slight operational differences and added features. Refer to ICM275 Component Layout (Page 3) for location of control center components.
Operation with new blower and humidifier relays:
The previous design control centers used a SPST-NC or DPST-NC heating fan relay (HFR of E2) and a DPDT cooling fan relay (CFR or 2F) for blower and humidifier terminal operation. This new control center uses a SPST-NO blower relay (BLWR) and a SPDT blower speed change relay (hi/lo) for blower operation, and a SPST-NO humidifier relay.
1. The low-speed blower will not operate on a transformer failure as on previous designs.
2. If JW1 jumper is cut between R and GH terminals, a constant low-speed blower will occur without any thermostat inputs to the control center. A GC or Y signal to the control center will not bring on the hi-speed blower for cooling operation. JW1 jumper must not be cut on cooling applications.
3. The humidifier H terminal is energized with low-speed blower operation. In cooling operation, the humidistat and humidifier water supply should be turned off to ensure the humidifier does not operate."


this is a link to what the old board looks like:







this is a link to how the new one is wired:


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