Electrical Issue with Sprinkler System

I have a five zone sprinkler system that includes a controller (Richdel model 446PR) and a pump that pulls water from our backyard pond.
The controller can turn the pump on and off by toggling a relay switch connected to the pump. The relay switch has not been working. When I disconnect the wires from the relay and test them with a voltage meter, it registers 28.5vac. Since it's a 24vac relay, things should be fine. But when I connect the wires to the relay the voltage drops to 8.5vac and cannot flip the switch. Does anyone know why the voltage drops like that?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.