Thanks for your question. I'm assuming this isn't as simple as the pedal drawbars being pushed in or pedal volume being incorrectly adjusted. Since this organ is at least 30 years old it is probably an issue that is due to age. These kinds of organs are also subjected to frequent moves and less than ideal environments at some point over the course of their lives. Do you hold a pedal as the organ is warming up each time you turn it on? Do you still have volume issues if you turn it on regularly, warm it up and then play after the organ is warm? The pedals, simply because of frequencies will draw more power, so you should always let the organ warm up completely before playing any notes.
It is impossible to diagnose something like this over the internet. Your best bet is to contact Hammond regarding this. Unless you are pretty experienced with fixing these kinds of instruments, repair is best left to one of their authorized technicians. As i'm sure you know, there are a lot of "guts" in these organs that are quite delicate. The Hammond website has a form where you can submit a question to them via email and have it answered by their service staff, here below:
In addition, you can use this link provide below to find the dealer closest to your location. Most dealers have technicians who work with the company or on behalf of the company to service the instruments in that particular area. You might want to contact them too to find out about a service call.
Either way, I hope you get your issue resolved--best wishes! Please click accept if this answer has been helpful to you. If you need additional assistance or clarification, please click reply so I can continue to help you. Thanks!