size of pipes in Auto HVAC system

[pramodkhatal]

In an automobile air conditioning system why the size of suction pipe is bigger and the size of discharge pipe is small?

[SBKold]

It is the same in most refrigeration systems as well.

We size with low pressure drop thru tubes in mind.

Since suction line is relatively low pressure and usually the longest it is also usually the largest diameter.

[pramodkhatal]

In an automobile HVAC system, how the expansion valve capacity decided? what criteria used for that?

[SBKold]

I would assume they match it to compressor capacity as well as evaporator size and blower capacity.

Then they figure out what superheat spring.

Or it may be just grab one off the shelf. I say that because cars with rear ac don't seem to have larger compressor or condenser.

[toocoolforschool]

Higher pressure less volume, high side. Lower pressure more volume = low side

[54regcab]

The rpm of the engine controls compressor capacity to a large extent.