Trane HP Defrost Board Problem

Amazing to have joined the board just in time to post the first question on the Heat Pump Forum.

I have an 18 yr old Trane heat pump with a 21c140501 defrost control board. The outside fan will not run. Using multimeter I have determined that the NC relay on the DFC board is open. Haven't determined yet whether the relay is bad or something in the defrost control is calling for the fan to be stopped. The red led is flashing three quicks and a pause. On my other units the led gives a steady flash. I presume that is an error code.

I jumpered the relay out of the fan circuit and the unit appears to be functioning normally. I will need to repair before heating season. An new OEM board is $360 so I really would like to know if I need it before shelling out the bucks. Any advice on troubleshooting would be appreciated.

Regards, Ed

Are there any temperature sensors within unit that may be holding off operation? If so, check them out, but on the other hand then you will have to fork out the dollars for new pcb.

Jase

Hey, Ed
I'm working the same exact problem. I'm trying to cross the board to a replacement on the net. So, far I've found a board on a site. Do a search for a 21C140501G04, and you'll find what they recommend as a cross.

Let me know if you find a cheaper control board.

Thanks for the replies. Phasegordon, I see the alternate pn. At least it's half the price. Thanks.

I plan to pull all the inputs and power to the board and check to see whether the relay is still open. If it is I will replace just the relay. If not I will try to figure out how to troubleshoot the temp sensing circuits, I'd hate to replace the board and find out I still have the problem.

Regards, Ed

Ed,
I am having the exact problem with Trane defrost controller board. I am wondering if your search for the replacement board was successful and if the replacement part has worked ? Thanks
LaVar

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Originally Posted by FastEd

Amazing to have joined the board just in time to post the first question on the Heat Pump Forum.

I have an 18 yr old Trane heat pump with a 21c140501 defrost control board. The outside fan will not run. Using multimeter I have determined that the NC relay on the DFC board is open. Haven't determined yet whether the relay is bad or something in the defrost control is calling for the fan to be stopped. The red led is flashing three quicks and a pause. On my other units the led gives a steady flash. I presume that is an error code.

I jumpered the relay out of the fan circuit and the unit appears to be functioning normally. I will need to repair before heating season. An new OEM board is $360 so I really would like to know if I need it before shelling out the bucks. Any advice on troubleshooting would be appreciated.

Regards, Ed

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I think you can fix these boards, by replacing the 2 onboard capacitors and the large power resistor. I fixed my board by doing this.
The reason why, is that the electrolytic caps, age and wear out after many years at high temperature. The IC doesn't work so good without good filtered power. The IC controls the relay.

Phasegordon, do you have the specs handy for the caps and resistor? Is your repair still working?

I have to do something soon it's getting cool in FL. With the relay jumpered I stay in AC mode.

Regards, Ed

You should be able to find the board in question at a price below 360 bucks.
If not, send me the model number of the H/P and I'll see if I can get you a board at a better price than that.
Replace the board and avoid future problems with other resistors or components on the board in question.
Once one portion of the board circuitry begins to fail, other problems with it are sure to follow.

I'm having a problem with my heat pump that the local AC technician has diagnosed as a "bad control panel". The part is a 21c140501g04, same as discussed in this string. The panel is displaying three short flashes. What is happening inside the house is that the AC ceases to blow cold air when it gets really hot outside. Seems to work fine at night and in the morning, however.
My question is if this is really what is wrong with this unit??? I ask because I have located a replacement board, but it's $187 plus $100 shipping, nonreturnable. I want to be sure before I spend that much money. Aqny help would be much appreciated; it's really hot here!