Dual Evaporator Requirements

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coolcoolcool
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Joined: Fri Jun 18, 2021 5:40 am

Re: Dual Evaporator Requirements

Post by coolcoolcool »

yea good question. i would also like to know.
Al9
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Re: Dual Evaporator Requirements

Post by Al9 »

Two orifice tubes would likely lead to serious pressure imbalance and charge migration issues in certain conditions (for example leaving only the front system operational, and turning the fan off on the rear one yet leaving it with a live, that is, refrigerant fed, evap) and basically end up in no cooling for both systems and possible compressor damage. Keep in mind an O/T is a fixed restriction unlike a TXV, so using two different O/T sizes will likely solve some of these problems and create others.

Even when only TXVs are used on both evaporators, they have different control parameters (for ex. a different MOP).

An O/T controls refrigerant flow in different way than a TXV, and so do two TXVs that have different control curves. So it's unlikely that the two of them will interfere.

Generally speaking, it's known in the art that two control systems that have the chance to control within the same operational window will try to control each other and effectively "fight" each other, making the system severely unstable.
That is also the case of a classic, fixed-superheat TXV and a V5 variable displacement compressor. In certain weather conditions, that TXV will repeatedly hammer fully closed and then open partway to keep a certain superheat, and the compressor's control valve will go haywire due to the severely unstable suction pressure. A suitable TXV will never close fully within the control valve's control window, either due to an appropriate control charge curve that features a superheat drop at low heat loads (common), or due to deliberate valve seat leakage (very rare).
coolcoolcool
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Re: Dual Evaporator Requirements

Post by coolcoolcool »

hey who deleted my question from the forum about ammonia r717?
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Tim
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Re: Dual Evaporator Requirements

Post by Tim »

coolcoolcool wrote: Fri Jun 18, 2021 8:50 am hey who deleted my question from the forum about ammonia r717?

I did.

illegal substance for Auto AC Systems.
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tbirdtbird
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Re: Dual Evaporator Requirements

Post by tbirdtbird »

Would not work anyway.
gm76
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Re: Dual Evaporator Requirements

Post by gm76 »

Thank you Al9 for advancing my learning curve. I also learned recently about about (Variable Orifice Tubes) and installed one with good success. Now my R4 doesn't try to lock up once in awhile like it used to and maintains steady gauge readings. For now, I backed off of the rear AC system idea and decided to just use the coach roof AC with a (Soft Start Device) running off either the generator or inverter, whichever works best. Thanks for all welcomed responses !!!
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