carrier blower circuit board relay

[Nicky]

The heating and ac wont come on at all but the blower fan will come on in when the fan is in the on mode.  when cutting the power on and off to the unit at the cover safety switch when calling for heat or ac the blower motor kicks on for about 1/2 a second. For the short time it kicks on there is a spark in one of the relays on the circuit board. Does it sound like a bad relay? This is the only time there is activity to the unit besides when calling for fan. The relay is soldered on i believe and its a potter brumfield kup-11a17. I've seen replacement circuit boards and read at least once that there may be a couple of differences on the new board and it may not be as straight forward as an exact replacement. This is not confirmed though. circuit board model number is hh84aa005. I've soldered new pb relays on jacuzzi circuit boards. Is this relay available or doable?

[JJDH]

Replace the board.

[Nicky]

ya, i checked and i can get a new board for 56 bucks. I can also get a relay if i have to but may not be worth the time. The new board at my appliance house that crosses with my old number is icm275c. So if this relay controls the blower in the heat and cool auto modes and it's contactor is bad does this also prevent the condenser and the gas valve from getting power to come on? thanks

[ACtechGUY]

One oddity of some control boards is when they are powered up they will "bump" a motor. Very disturbing when a blower turns on for a split second and then back off when you have a different problem......

I say don't worry about the fan coming on when the system is just powered up. You have another problem.... The control board does not control the signal to the condenser directly. If you get no condenser , then you have a problem the 24 volt control circuit from the heater to the thermostat. Check that your themostat is functioning correctly . Place a jumper from R to Y at the themostat first and at the control board. cooling should come on . if it comes on when jumper is placed at the thermostat, then your problem is the themostat, if it comes on when the jumper is placed at the control board , then you have a problem with the wire between the board and thermostat.

The fact that the blower operates in "fan on" mode leads me to beleive that the problem lies in the themostat.

[Nicky]

 

i installed a new circuit board. The old board see through relay had obvious visible problems. The new circuit board enabled the ac system to work now, the "fan only" still works, the slight fan kick on disappeared which is all great but the heater wont come on at all still. The thermostat that was reading AC on the display, which in the manual indicated a lack of 24 volt power to it also disappeared and it now shows the temp and system on light comes on also. I bypassed the thermostat and the heat still wont even react. no spark, absolutely nothing. what else can it be? If the spark ignitor is bad will this stop voltage to fan and valve? thanks

[ACtechGUY]

Without knowing exactly what furnace you have , it is hard to say what to do.

Did you jump out from W to R at the board?

There are usually several safty devices inline with the ignition circuit of the heater. All safety devices should have continuity when checked with an ohm meter. some safety devices are manual reset types. Many older furnaces also have a fusable link somewhere above the burners . If you have a open / failed fusable link or a tripped manual reset hi temp switch, you may also find you have a failed heat exchanger.

[Nicky]

i jumped r to w. i also checked the high limit with an ohm and its ok. didnt do much else. Its a carrier unit installed in 85 i do have the model but not handy at this moment.

[ACtechGUY]

The way heating logic works is ---- Heat input from thermostat---- Heat signal trys to go thru all heat safeties(fan limit, fusable link, rollout switch)---- if ok, then signal passes to ignition system ----- pilot flame ignites and burners come on... the end.

Carrier furnaces have multiple safeties in line with the heating circuit. The model number will start with a 58. the 58 translates from Carrier to human as "GAS FURNACE".

If you find one of the safety devices open take a look at the ribbon burners. Do you see rust piles on them??? Look up into the heat exchanger , do you see any holes ??? If you have either you might have a dead furnace. If you do , STOP NOW and call a heater guy.

[Nicky]

This furnace was working fine a week ago. I guess the bad relay was becoming evident though, because the blower was hesitating at start up. When I looked at it nothing worked except the fan on mode. After the circuit board was replaced the ac blower and condenser worked now the heater function on the readout on the thermostat even reads on now, but nothing going to spark or gas valve. Is this just a coincedence that there is another problem? It is so frustrating because I cant spend a lot of time on this because of so many other pending jobs i'm doing and I have a sneaky suspicion it's going to be something simple. I'm very interested in this fusible link or whatever else sends power to, or prevents power to ignitor, valve fan.