ICP Furnace Showing 80% Limit Fault
December 8, 2025
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Most gas furnaces have several safety limits, main limits, roll-outs, 80%’s will have a DSS (Daft Safety Switch) These safety
This phrase can be an assortment of items on our 48TC package units. After the inspection of the unit, you see the charge is okay, No broken belts and all main voltage is present. Now after bumping the contactors, it shows everything is operational. It is determined we have an electrical issue which for most technicians not a strong suit.
We are talking today on our electrical mechanical board shown below. Once you know the inside working, this board is very easy to master. The First step after verifying you have a call for cooling. The unit runs through the unit shutdowns. These are on the right side of the board they consist of the Smole and Remote shutdowns. If those are good, then it will send power through plug 1 on the Econ plug. Then it comes back through at 2 on the Econ plug. This is a 24-volt signal. Once verified there it goes to jumpers 6 and 7 if there is no reheat on the machine. If it is present runs through terminals 5 and 6 on single compressor units. Terminals 7 and 8 for dual compressor units. Once it passes through it will start the fan. This will then go from terminal 6 goes into terminal 4 on the compressor plug. This runs through the high and low-pressure safety. Once cleared there it goes out terminal 6 to the fan-providing switch mounted on the squirrel cage of the blower. This is closed the compressor will start.
With the knowledge now of this board. When you run into a unit not working the wiring schematic will not be as daunting to negotiate. This style control is the most common you run into on the 48tc units. But this is also a common board in multiple carrier package units ranging from 3 tons to 20 tons.
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Most gas furnaces have several safety limits, main limits, roll-outs, 80%’s will have a DSS (Daft Safety Switch) These safety
This article is in reference to Residential Heat Pumps. Everyone in the HVAC industry knows that the indoor TXV
Compressors are the heart of the refrigeration system. It creates the pressure difference to move the refrigerant through the system.