steam coils, freeze stat tripping

Grega

Have a make up air unit with 3 steam coils. Very old air handler. A new motor and frequency drive was added last summer. The coils are fed individually and have modulating valves. Steam traps are working, strainers are clean, new stat with same result. Have slowed motor speed, any suggestions. There are no vacum breakers, but it worked before new fan motor and pullies.

nicholas bonham-carter

What is it not doing now which it did before?--NBC