water pump system, stuck on hose sizes

This is for a water condensing unit, where the condenser will be placed into a area with high humidity. There will be a t section for bleeding etc but haven’t placed this in the diagram.
Pump is a small 12v 1GPM 9 foot type of inline pump. I’m trying to get the most out of the pump, the total length of piping will be about 9 foot roughly, that is accounting for coils in radiator and condenser.

Please see link to a quick sketch up model
https://www.flickr.com/photos/66229633@N03/11292760175/

Radiator has a choice of id fittings, gone with inlet and outlet of a id of 13mm.
My pump will only allow id 8mm tubing both sides.
My condensing coil also only allow id 8mm tubing both sides.

Will i be better using all id 8mm piping? I thought that if i had larger piping on the return it may help the pump with the gravity fed pulling water through?

Also the red tubing, would this be better as 8mm or 13mm?

Regards jon

Since no one has answered, I’ll hazard a guess, and at least give you a bump:

Use 8mm id throughout. The total flow of water has to be the same throughout the loop, and 13mm id piping has 2.6 times the cross-sectional area. That means the flow rate will have to change by a factor of 2.6 every time you change id. That will cause turbulence, and add drag to the water flow, making the pump work harder.

I do not fully understand what you are trying to accomplish here and I hope this would be useful.

1> I would try to put the pump at the lowest point in the loop - so that the pump is not sitting on an air pocket (it looks like it is right now).
2> I would recommend that you run the 13mm pipe to the pump inlet and then put an reducing adapter there. If possible, put a small filter there.
3> Recommend a valve at the discharge of the pump - this will help you increase resistance in the loop and adjust the flow, if needed.
4> Would also recommend a vent at the highest point in the loop - or you expect air can accumulate anywhere - provide a vent to remove it.
5> You already have the T - section - so thats great
6> Wish you can add an reservoir near the pump inlet that has an air space and you can monitor the level. The air space will help with ambient temperature changes and you can also add water (hopefully it has some kind of bio-cide in it) through this.