I am modifying a mini cooler/heater to turn it into an incubator in which I can program the temperature sequence in time. I have reconstructed the electric diagram of the cooler/heater and I don't understand why the maker chose to include the circled diodes. Here is the diagram: Mini cooler/heater diagram, a switch controls whether it works as a cooler or heater

There is a switch which controls whether the heater works as a cooler or as a heater, resulting in the two different wirings shown in the figure.

I don't understand why the maker used the circles diodes, being that the following diagram should do the same job, without needing the diodes: Simpler diagram, this should do the same job without needing the diodes

The wiring would be as in the figure above, depending on whether it's a cooler or a heater.

My question is: is there a reason to prefer the maker's design to the one I propose?

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    \$\begingroup\$ Good point. Maybe there was a third position in which everything was off? Also, why the resistor? \$\endgroup\$ – Wesley Lee Feb 7 '17 at 21:21
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    \$\begingroup\$ The diodes are for the fan. They ensure that whichever way the switch is connected, the fan still gets power, and also allows for an off position where nothing runs. \$\endgroup\$ – brhans Feb 7 '17 at 21:22
  • \$\begingroup\$ That's it, I didn't think about the OFF position, which is the third option for the switch. Thank you! \$\endgroup\$ – Andrea Feb 7 '17 at 21:38
  • \$\begingroup\$ Uhh your circuit won't work because you can't put a resistor before the fan. The fan motor just won't work. \$\endgroup\$ – Bradman175 Feb 7 '17 at 21:55

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