Automotive Air Conditioning Information Forum

Y'all know we do a lot of AC work in this shop and have every kind of certificate shy of a MACS, and plenty of equipment.

I usually retrofit vintage cars with Old Air kits. they are 30 min from my shop.
Thought I'd try VA for a change.
Please recall that in summer Texas heat we can easily go to 100-103 on a summer day in North Texas, hotter and more humid in south Texas.

1) So the VA instructions say the system low side is gonna be 10 psi, which it certainly is. This is clearly a function of how the TXV is set.
My problem with that is low mass flow, and low oil return. Also, a low of 10 psi will promote evap freezing. I have no intention of killing the nice new comp and since everything is already installed, I removed the insulating tape from the TXV bulb, and that got my low side up to 20 psi. My retrofits using Old Air are always about 30 psi. Next time I have that TXV off, I will turn the adjusting screw 1/4 turn CCW to open it up more.

2) The thermostatic control has the diff set so high it is ridiculous. For example if I set the temp to 38°, the diff will not allow the comp back on until the evap hits 58 (20° diff). This is not acceptable in 100° heat as it is today.
I am in the process of removing the thermostatic control and adjusting the diff, as I know full well they can be adjusted. I am thinking 10° max would be much better.

Thoughts, anyone? Appreciate input.
Dave

hi
1/ some factory fitted run low ,low side pressures with no ill effect . Assuming its all about heat load and air flow plus evap design . Rule of thumb is 20--35psi .
On an after market kit I would be suspicious .

2/ temp rise after compressor switch off [hysteresis]
3-5deg cel .. 38-40f diff with a thermister [electronic sensor ]
4-8 deg cel ... 40--47F diff for a mechanical thermostat

My Ranger 06--12 model diesel [Ford Thailand ] compressor off at 3-5 deg cel ----compressor on 5-8 deg cel --- MAX diff is 5 deg cel =41f
In my exp Toyota Nippon Denso a/c is far far better accurate and has way more consistency .

I think their evap/blower doesn't have enough capacity. To compensate they allow it to run below freezing and build ice/frost in the fins. Long off cycle that will occur because of that large hysteresis will allow the ice to melt at each cycle.

I agree it's hard on the compressor, but if I was trying to shove a small evap/blower unit into a classic car maybe I wouldn't mind being hard on the compressor. I can buy a new compressor, but I can't make my wife ride in an uncomfortable car.

Excellent info from both of you, appreciate it.

Right now, with my workaround to get the low to 20 psig, and my fiddling with the cutout, at 100° ambient, I am at a constant 37.2° center vent, it doesn't change, which means heat in=heat out. I sure could have used that vent temp yesterday while on a trip to Dallas.

Maybe the VA engineers are not trying hard enough?
This is a big ol' '59 Caddy with lots of glass and interior space.

Not a lot of info about the system. But 1959 Cadillac you say?

https://autoacforum.com/viewtopic.php?f=3&t=13477

Start there.

2xo, thanks for responding. That was a good thread.
I fabbed the system.
Used Vintage Air proprietary evap., temp switch, and TXV. (it is a kit)
Sigma 14-SD4709 new comp (Japan) from Tim. R134
Omega 14x24 PF condenser, largest that will fit.
I added a fan shroud, and a electric pusher fan in front of the condenser. Fan is on if comp is on. Condenser is tight to the radiator, with air dams all around.
TXV and mechanical thermostatic switch were set to Vintage Air specs. Poorly done in my opinion. Now modified by me as above.
Works quite well now that I have fine tuned the TXV and thermostatic switch

Ambient 100
max fan
max load doors open
At 1500 RPM Lo 20 Hi 250-275
Center vent now a steady 37.2°

Nothing Cadillac about it. The car never had an A5. I got A6 mounting brackets from a junkyard in Minnesota and then used an adapter bracket kit to convert the A6 mounting to the Sigma 14-SD4709 mounting.

The system works well, now that I have modified the controls to my liking. I wish those 1 ton TXVs were externally adjustable

hi
A 1 ton txv seems a little on the low side . Although the Tx is suppose to be matched to the size of evap . I would try a 1.5 ton valve.
Aftermarket suppliers can have several different sizes of evap cores . Hoping u have not installed a unit thats to small .

Lowering the high side pressure to below 200 psi will improve performance of evaporator ie be able to handle high ambient temps easily .
high pressures operating at 150--160 psi only usually happen in a custom / dual condenser but give outstanding hot weather performance .

Electric fans Use as many as possible with a minimum diameter of 11--12 inches if not bigger with a minimum of 13--15 amps each
There are 20--25amp units of similar size
10 --12 inch fans of around 10 amps DONOT work

Aftermarket Mechanical thermostats typically give poor performance as I mentioned earlier [some vehicle maker units are surprisingly good ] .
A thermistor allows the evap temperature to be pulled down lower [compared to mech unit ]which is alot closer to the freezing point .

Evaporator design is similar to condenser design . Modern units are parallel flow . This started way back when R134a first appeared .
Tube and fin need to be huge to work properly . This design is very inefficient . They are cheap to produce .

Appreciate your comments.
The system is working very well, indeed.

As an aside, I have found it very difficult to get ratings on automotive TXVs. There is precious little documentation of anything any more.
But no matter, the AC is excellent