User manual for Environmental Chamber Delta Design 2300R

Hi, I have gotten my hands on a Delta Design 2300R environmental oven
however I have no handbook and am having some trouble getting it to
operate correctly. When the oven is cold I can set a heat setting and
it will tend to reach this operating temperature. However once the
temperature has been reached the oven seems to cease to maintain the
temperature until the oven reaches below 30C again (quite a while). Is
there some setup that I need to do or can anything be gleaned from
what looks like an RS232 port at the back ?

Thanks,

Robin.