What happens when capacity of system is exceeded?

[cyfi66]

I am curious what happens to system conditions when the heat load on the system exceeds the design of the system? My system is in good working order regarding charge, condenser airflow etc. but still doesn't get as cold as I would LIKE it to when I am in the middle of a hot summer day in Arizona, just hopped in the car after sitting in the sun etc.

What I notice is that with everything full blast after baking in the sun the suction line doesn't get FREEZING cold, just cool, at least for about 15 minutes. I know this may be considered "normal" but I am also wondering from an engineering perspective, what happens when you put more heat load on a system than it was designed to handle? I would assume low side and high side pressures would go up which increase the boiling point of the refrigerant in the evap.

What I am seeing though is high superheat under these conditions. Good low side pressure (35psi) but suction line not cold, solid liquid in the liquid line though. This tells me the evap isn't being flooded. Is it possible the TXV is wide open (max open) but at its max open state is still not enough to allow enough refrigerant through during high heat loads? It almost seems like the TXV is maxed out and wont allow enough refrigerant into the evap - not because its bad but because it was only designed to work up to a certain heat load.

[tbirdtbird]

"was only designed to work up to a certain heat load."
Every system AC or not has a design limitation.

Please consider that after the car has baked in the AZ sun for a few hrs the entire car, ie seats, dash, floor, upholstery, under hood, everything will be at that high temp. It is called heat soak. There is no way the AC can pull down everything all at once. Same is true for a house. Friend bought a house in FL and it had not had the AC on for 2 weeks when they got there. They turn on the AC and they write me it is not blowing cold. Well, simply, it can't. I said wait a day or 2, and it will. And it did.

Tim and a couple other experts here live in AZ let's see what they say about parking your car in the sun, instead of shade

[cyfi66]

The main reason I ask is I have another vehicle that despite the same conditions will pump down the vent temperature almost instantaneously - like within 60 seconds the air out the vents will be very cold, even when the interior temperature is upwards of 150 degrees.

The main thing I want to know is "what's different". I know there are a lot of variables but why is one able to get cold so fast and one not? I'd like to re-engineer my system to pump down quicker, whether that be by increasing the compressor displacement, increasing condenser size, larger TXV etc. The problem is there is very little literature publicly available on auto AC system design and sizing, it seems most of the manufacturers keep that to themselves.

I am more than willing to "sensor up" the system to figure out where the weak points are so I can upgrade things as required. Problem is that even with the data I wouldn't know where to start.

[tbirdtbird]

I strongly suspect the other vehicle is a different make. Hondas, for example, are known to have inadequate engineering..
If you were able to fit a comp with more displacement, then I suspect your evap and expansion device and certainly the condenser would also have to be upgraded. You would be starting over

You actually have not supplied the make model yr of the troublesome vehicle. The pros here may be able to identify a weak point right off the bat

What is wrong with lo of 35.
Are you using a pro manifold set or just that silly little gauge on a charge can, which are never accurate.
If you can provide both hi and lo at 1500-1800 RPM that gives us something to chew on, and vent temp. Charge might not be correct, you might have slow leak.
Fans running as they should? Did this car ever work to your satisfaction?
Mist down the condenser and get another set of readings as above while misting.

Lots of missing info here

[cyfi66]

I didnt really want to turn this thread into a diagnosis thread which is why most information was left out. The system is in good working order, and isnt troublesome, its merely not as good as I want it to be.

In fact when I park in the shade on a 115 degree day or drive the car for 15 minutes, the AC performs well with vent temperatures down below 45 degrees. This tells me its working "properly". The pressures are within specifications and condenser airflow is excellent.

High superheat during the first 15 minutes of driving after heat soaked in the desert sun is my "complaint". Good systems pressures but superheat of 20+ degrees during the pump down time.

I am hoping some can shed light on system design and how to increase the cooling capacity. If I want to upsize the system from scratch as you say, how would I determine how much sizing increase is needed in each component and which components being upsized have the greatest effect on system performance?

Since readings are supposed to be taken after 10 minutes of operation anyways these readings wouldnt really add to this discussion since by then the system is cooling OK. I am only concerned with reducing the pump down time.

[tbirdtbird]

"I am hoping some can shed light on system design and how to increase the cooling capacity."

I seriously doubt anyone can do that without make/model/year info

[Tim]

"I am hoping some can shed light on system design and how to increase the cooling capacity."

I seriously doubt anyone can do that without make/model/year info

I can! Remove everything out of the vehicle. Install a 5 ton home or an industrial unit in the cab. Then pull a trailer with generators. To power the 5-ton unit.

Problem solved.

[Cusser]

"was only designed to work up to a certain heat load."
Every system AC or not has a design limitation.

Please consider that after the car has baked in the AZ sun for a few hrs the entire car, ie seats, dash, floor, upholstery, under hood, everything will be at that high temp. It is called heat soak. There is no way the AC can pull down everything all at once.

EXACTLY

Tim and a couple other experts here live in AZ let's see what they say about parking your car in the sun, instead of shade

I'm in Arizona, and that's definitely a difference like night v. day !!!! I always look for a shady spot, even if 3 times the distance from the store. And here in Arizona, parking away from the crowds means one will be less likely to have their vehicle hit and the perpetrator simply drive off !!!

[tbirdtbird]

car-ac-mcgyver.jpg (61.3 KiB) Viewed 8483 times

[Tim]

There is no magic trick to achieve an ice box. Vehicles are limited to so many factors. I jest only because this has been discussed for 30 years now. Still, the same issues, lower head pressure and have a giant evap core.

Oh, park in the shade.