Automotive Air Conditioning Information Forum (Archives)

defrag010 on Thu August 25, 2011 11:44 PM

Year: 1991
Make: Eagle
Model: Talon
Engine Size: 2.0
Refrigerant Type: converted R134
Ambient Temp: 105+
Pressure Low: n/a
Pressure High: n/a
Country of Origin: United States

I am not formally educated on MVAC systems, but I am self-educated with the proper basics enough to successfully troubleshoot and service both of the a/c systems in my daily driver vehicles (1992 Lexus SC400 TXV system converted to 134 blowing high 30's on the interstate at over 100 ambient, and 1997 GMC k1500 CCOT 134 system blowing low 40's on the interstate at over 100 ambient).

What I am working on is my '91 AWD Talon project car which will use an air to water intercooler. I live in Oklahoma, and this July was recorded as the hottest average monthly temperature in any state in the whole country ever. Record setting hot summer, with a whole week of straight 110+ temps. As you can imagine, this really takes a toll on a/c systems. What it also takes a toll on are water intercooler temperatures. In this heat, even with a big heat exchanger, the coolant in the system won't be able to get cold enough to yield intake air temps lower than a comparable air to air intercooler system (which has always been a benefit of water intercooling). After brainstorming for a while, I came up with a solution: add a second evaporator submerged in the intercooler coolant reservoir to chill the intercooler water. After days of googling, I stumbled across a company that produces similar water chiller kits for factory supercharged ford vehicles that use orifice tube systems (killerchiller.com). They have two kits available. One places an evaporator in series between the condenser and the cabin evaporator. The compromise is a higher cabin evaporator temperature. They also make a "Drag kit", which consists of a switchable T-fitting at the condenser outlet that can run both the cabin evaporator and the add on evaporator (with add on expansion valve) at the same time, or bypass the cabin evaporator to divert all the refrigerant to the add on chiller evaporator. These kits seem to work very well, but because they are both run like a stock system (preventing the evaporator from freezing), the lowest water temperature achievable is reported to be 44 degrees. This is great, and yields sub-ambient intake air temperatures, but I have an idea to design a similar system for my car to improve on their design and allow sub-freezing water temps using antifreeze coolant.

Where my research meets a dead end is the difference between a steady state refrigeration system where you use TXV's and EPR's to set each evaporator to the right pressure and a constantly changing air conditioning system in a car. This is why I signed up on this board to ask this, hoping for some insight from professionals.

I plan on doing a full 134a conversion by using a Denso 10PA17, condenser, and cabin evaporator/TXV from a 1995+ car (all of them are a direct bolt in to my earlier model chassis, with a slight modification needed to get the evaporator to fit) and making my own 134a compatible lines. I have the manual mastertool crimper so I can make the lines myself.

Where I am hung up on is how to implement the second evaporator for chilling the intercooler coolant. My thought is that since the evaporator will be submerged in antifreeze, that it will be able to go below freezing without consequence since frozen condensation blocking flow will be a moot concern.
-Is there a TXV that is either preset or adjustable to yield a lower temperature like maybe 10-15 degrees? Could I use a stock expansion valve and just place the bulb somewhere downstream (maybe at the cabin evaporator inlet/outlet) where the line temperatures would be a little warmer?
-If that is not possible, would it be feasible to just put an orifice tube in front of the chiller evaporator and just let the compressor draw the evaporator pressure down as far as it can? I could put a STV on the cabin evaporator to limit the suction it sees so I wouldn't draw the cabin evaporator down too far. Maybe change the low pressure cutoff switch to cut off when the low side reaches a vacuum.
-Will the compressor be able to keep up with the demand of a cabin evaporator at full load as well as a smaller additional chiller evaporator being drawn down below freezing? Will I have to use larger diameter lines on the low pressure side to support the refrigerant flow?
-If the chiller evaporator is running at low enough pressure to yield sub-freezing temperatures, would I need to put an accumulator after it to let the refrigerant boil off before entering the compressor suction side? If this is needed, maybe I could run a stock expansion valve and place the bulb after the accumulator so that it would cut off flow to the evaporator at the refrigerant boiling point.
-How much will this change the system capacity, and how will I determine the new capacity? Is there math, or would I just use the old school vent temp method?

I really appreciate anyone who has read this far and who could possibly have any input on how I can accomplish my goal. I would be thrilled to be able to cruise around next summer in 100+ degree temps with my intercooler system cooling at freezing or below!

Edited: Fri August 26, 2011 at 2:04 AM by defrag010