Not only is that model discontinued.......there are absolutely NO repair parts available as per Harbor Freight customer (alleged) service as of 04/14/2012
Replace the rubber gasket. Inspection of air valves. Compressor control.
There are many gaskets on any machine. Is this an electric compressor? Once you find what gasket it is specifically, you simply need to remove that part, and add a new gasket, then put the part back on...
Try http://www.victorreinz.com/products.html, they offer a variety of head gaskets, which are still in production for older models.
at your local napa store
It's probably the intake manifold gasket gone bad. Not uncommon.
check the upper intake manifold gasket you will need to remove the ac compressor to check this
Let's see...cracked head, cracked head gasket, cracked intake gasket, bad cylinder liner or cracked block, air compressor head gasket...if this was a Cat 3116 I'd also look at the oil cooler or an injector sleeve, but it's not so that's probably not it.
Bad head gasket or cylinder head. Suggest to check air compressor before working on the head.
Disconnect the oil and air lines to the compressor, disconnect the fuel pump (if yours is attached to the compressor), remove the bolts holding it in place, clean all mating surfaces of any remaining gasket material, transfer any fittings from the old compressor to the new one, and reinstall it.You want anything more specific, we need to know which engine and which model years, as some models with the MaxxForce engine used a non-unloading compressor which was driven by the flywheel.
intake gasket
A blown fuse, lack of refrigerant or a blown gasket on your compressor to name a few.
there are three bolts under the transmission case by the converter clutch butterfly valve take them off and its under there but make sure you have completely removed the gasket