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Working on the old girl and noticed that the a/c compressor was not engaging,so I ran a jumper wire and it engaged. I started looking in the top of the cab and after chasing power everywhere with nothing coming out of the cut out relay to the compressor. I changed it still nothing unless I unhook the ground and then it cycles but the fan does also but only on purge, put it on high and compressor and fan runs continuously. Could it be fan speed switch or something else I have replaced the thermostat switch also with no success. Thanks for any suggestions.

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What is red light doing.  On or off.   There are several things that can be hooked up wrong and it will still work some what.  I would get a hold of a wiring diagram for that system as IH is one of a kind with their low and high pressure controls. Not your ordinary bear.  If it still has original lockout relay it is easier to understand but the superceeded one is a little more difficult to trouble shoot.  

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Red light is on when thermostat is on max cold about half way back to off the light goes out. I did replace with new style lockout relay. I have a picture of the diagram on my phone everything appears to be hooked up correctly but I could be missing something.

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Check charge first if that is correct check the low pressure switch. Run it with gauges connect to monitor pressures. Had to replace the lower pressure switch in the 3388 this spring. Pressures were correct yet the light was tripping on. Different low pressure switch took care of the problem.

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Sounds like a few things.  First it needs a charge, second the fan speed switch.  The fan switch supplies power to the thermostat switch when you turn the fan on.  There's one wire coming off the fan switch to the thermostat, check to see that it has power through all the speeds.  

 

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