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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
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Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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i have a 4ton rheem heat pump condensor (RPNE-048JAZ) about

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i have a 4ton rheem heat pump condensor (RPNE-048JAZ) about 5-6 years old and it stopped blowing cool air today. I reset the unit at the breaker and the defrost control board is giving the code for Coil Sensor Failure. I checked the air filter (dirty) and cleaned it but still get the same coil sensor failure error & warm air blowing. Any suggestions about what else I can check or replace?

Brian HVAC Guy :

Hi, I'm Brian. I'm here to answer your HVAC question to your complete satisfaction! Are you receiving my chat messages today?



Brian HVAC Guy :

Ah great. Chat hasn't been very reliable lately. The defrost control board on your unit can lock the compressor out. I have never run into a coil sensor that was failed. It would seem that the board wouldn't lock out during cooling for that fault but it appears it does.

Brian HVAC Guy :

Is your indoor fan running ok?


yes - fan at air handler has no discernible issues

Brian HVAC Guy :

it would appear that chat is acting up. I am going to switch to question/answer mode to make sure we receive each others messages.


I've had to replace this defrost control board before (about 2 years ago), similar symptoms although the code at that time was for (I think) High Pressure lockout (maybe it was low press lockout, can't remember)

Well there is one way to check whether it is the board that has failed or the sensor itself. The sensor should be connected to the board by two wires. If you connect a 10K ohm resistor in place of those two wires and the fault goes away and the unit runs then the sensor is indeed bad. That sensor is not needed during the cooling months it is only for defrost check and termination.
Customer: replied 4 years ago.

ok - I don't have 10k ohm right now - what wattage should I get? this is the low voltage side right?

Yes that should be about 5vdc a 1/8 watt resistor is fine there is no load on that sensor. I would still remove power before putting the resistor in and also remove/reset power to the air handler as well since that's where the control voltage comes from.
Customer: replied 4 years ago.

it's the sensor - I'll replace that tomorrow when I can pick up a new one. Any issue leaving the resistor in place overnight?

Well that's great news. A sensor is a whole lot cheaper than a new defrost board! I found some at Pexsupply online for like 4 bux and change but I'm not sure they are the right ones. That sensor isn't used at all in the cooling mode so there is no worry leaving the resistor on at all.
Here is the link to the sensor I found. I believe it is the right one.
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Customer: replied 4 years ago.

Excellent - Thanks for everything. My wife is hot... but now the A/C is working.

Awesome I'm glad to help. Look me up if you have any other a/c or heating questions! Thanks, -Brian