Defrost Clock Control

[gabriel84]

working on a walk in cooler condensing unit which is sitting on the top of the WIC. i was looking at the way the unit was wired and found myself stumped when it came to the defrost clock and t-stat. this was a pump down system so once the temp control was satisfied, solenoid closed, system pumped down and shut off.
what i'm curious to know is wires from both the temp controller (t/stat), and the defrost clock went to the solenoid which confused me because shouldn't one take precedence over the other. what i'm thinking is they are wired in series so should either of them open the solenoid closes and system pumps down. allowing for defrost. but i'm not sure.
if anyone has an answer and maybe even a schematic diagram they can send my way of how this is wired it would be nice
thanks

[SBEC]

It is common practice to wire the temp controller and defrost timer in series so that the operation of either the t-stat or the the defrost timer will open the solenoid and allow the system to pump down. As far as wiring diagrams and reading schematics, Manufacturers usually have them on their websites or they are available from distributors. Check out the local trade schools for an intro electrical course or controls course to gain a better understanding of electrical control. It also makes it easier to break down the electrical control circuit into its various subsystems to make troubleshooting easier.

[icemeister]

The thermostat and solenoid must be wired in series.

Here's a link to Heatcraft's I&O Manual:

http://www.heatcraftrpd.com/resources/wiringdiagrams/H-IM-64L.pdf

(See Diagram #1 on p.40)

[SBEC]

To make matters more confusing if you have multiple evaporators, then the defrost termination controls have to be wired in series also to ensure all evaps on the circuit receive the full defrost they need. Again that is covered in the Heatcraft link that Ice referenced.