Ingersoll Rand 2 axle Compressor Not Unloading

I have been asked to fix a compressor that is not unloading. I relied on my smart phone instead of my note pad and did not get a good model number but it was made around 2008, is Ingersoll-Rand and is 2 axles with a large engine. I believe it might be 825 cfm or maybe 750.

It does not want to unload so it is hard to start and if it does get running up to full speed the pressure goes over 200 psi until the relief valve goes off repeatedly, scaring everybody on the job site. The air receiver/oil separator gets very hot if this is kept up.

I have not even been able to find an owners manual for this thing online let alone any kind of service info. Any ideas?

Thanks

Ingersoll Rand 2 axle Compressor Not Unloading