Model: 300 ZX Twin Turbo
Engine Size: 3 liters
Refrigerant Type: R12
Country of Origin: Japan
I am an original owner of a 90 Nissan Twin Turbo and live in the San Fernando Valley area of Southern California, where triple digit summer temperatures are not unusual. My carÃ¢ÂÂs AC has always been weak, although adequate for most days under 85 degrees. When the temperatures get in the 90-95 degree range, it takes about 10-15 minutes for the car to cool down if it has been parked outside. If the temps get into the 100-105 degree range then on short trips the carÃ¢ÂÂs interior hardly cools down. If I can get on the freeway for a while, the carÃ¢ÂÂs interior eventually cools down. Recently, I changed the OEM radiator for a Toyo racing type radiator with about twice the cooling capacity. This made a significant difference in the carÃ¢ÂÂs AC efficiency but itÃ¢ÂÂs still weak in triple digit heat. My concerns and questions are:
1.Since the Toyo is twice as thick as the OEM radiator, the fan shroud now sits further back, with the fan almost entirely inside the shroud. What should the correct clearance be between the shroud and the fan?
2.If I change the 1990 condenser, intended for R12, for one made for a 1994 300 ZX Twin Turbo, intended for R134, and then refill with R12, will I gain any more cooling efficiency? Both are the same physical dimensions but the 94 condenser appears to be parallel flow type having more tubes and fins.
3.Will changing the evaporator to a 1994 evaporator help improve cooling efficiency also?
4.If I swap these parts out, should I also consider changing the receiver dryer and the blower under the dash?
5.From other posts on this forum, I gather that I should refill the system with the same amount of R12. Is this correct?
6.My motor really generates a lot of heat under the hood. IÃ¢ÂÂm also considering other aero type mods that will allow better air flow through the radiator, like radiator air flow guides, hood vents and engine shields under the motor. IÃ¢ÂÂm on my second engine harness and probably looking at a third one soon. Will any of these help improve air flow through the radiator and dissipate under hood heat?
Sorry for the long read. IÃ¢ÂÂve been on most of the Z32 forums but none of the posts address these issues. Seems most of their members are about half my age and are more concerned with reducing unsprung weight, going fast and getting the most horsepower out of their ZÃ¢ÂÂs. I just want to drive comfortably.
Not sure I'd start upgrading all those components before doing some further diagnostics on the current setup. To that end, you'll need an A/C gauge set to check the low/high side pressures.
First step - verify charge level. If you have a slow leak, find and fix it. However, you'll likely need a shop to recover in order to tell. And shops that deal with R12 anymore are getting harder to find.
I think you're right to check out the cooling system as well. A better check in that regard is to mist the condenser (with water) with a/c on high and a hot car and see if it drops the high side pressure like a rock. That'll tell if you have a condenser heat transfer issue to diagnose.
The job of the TXV is to keep the evap full of refrigerant. I know that low, low side pressure coupled with high, high side pressure indicates a blockage, frequently in the TXV, which will reduce cooling substantially. So after the cooling system check, I'd start with a gauge set and see what the low/high side pressures are doing. Problem is, this sounds like it may be a borderline case like I had with my '92 accord a few years back, so may be hard to spot with 100% certainty.
Edited: Mon July 14, 2014 at 5:50 PM by webbch
Thanx for the input. I have a typo in my text, it's a Koyo radiator. Not a Toyo. I'll follow your suggestions in a week or so but will have to go to a shop that's got the equipment. Actually, I'm reasonably certain she has no refrigerant leaks. I blew a high pressure AC line about one year ago, just before I installed the Koyo radiator. Scared the bejesus out of me, happened in traffic. It was so loud, the guy in a car next to me got out to see if it was his car. The line was replaced, the radiator changed to a Koyo and the AC system refilled. Do not recall if the receiver-dryer was changed since air obviously got into the system. The AC system has worked consistently since then with as I indicated above, some improvement in efficiency but I'll consider all these suggestions.
Those cars have a lot of nearly horizontal glass, which can generate a lot of heat to get rid of. All of that heat, along with the engine heat winds up in the engine bay.
The fan can be inside the shroud a fair distance without issue. As long as the back edge of the blades are nearly flush with the back edge of the shroud you should be good to go. Now, speaking of the fan make sure the fan clutch is working properly. If it is not locking up & howling when it is hot, and at cold start it is suspect.
Adding the later year model parallel flow condenser could help some, but improving airflow over the existing unit is a good place to start. Check the air path through the heat exchanger stack, and make sure that no air is bypassing the condenser.
Anything that you do to let the air out of the engine bay will help. Turbos generate a lot of IR heat. That heats everything near it. Adding vents to a hood can be tricky. You need to add them in a low pressure area for best effect.
If you are killing wiring harnesses, I would insulate the harness, and some of the A/C components underhood. I had similar issues with my Saab turbos. Insulating the suction line made a measurable difference in A/C performance. If the receiver/ dryer is located in the engine bay, I would insulate that as well. For engine bay hose & harness insulation I have always used Aluminum faced fiberglass cloth We went all the way to the moon with this stuff. Cut it in to strips, and wrap the line or harness. Secure it with metal cable ties, I use This type with great success.
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.
Blowing the hose was a pretty good sign that the condenser is overheating, likely due to a weak fan clutch. It takes a lot more air for good A/C performance than just to keep the engine temperature normal. The thicker radiator isn't helping since it restricts air flow. Parallel flow condensers work better with any refrigerant. That would be a nice upgrade if the fittings are compatible.
Thanx for the advice, will definitely look into getting adapter fittings for a later model condenser. All the AC components are over 20 years old and since I plan on keeping the car for at least 5 more years, it might be a good idea to change them out anyway.
Just thought I'd post a follow-up. Mid summer, I added a radiator air guide. These are flat plates that seal the top gap between the front cross member and the radiator. According to their literature, they are supposed to drop water temps by about 4 to 5 degrees. Well that's too small a change to see on the water temp gauge but since they force more air flow through front heat exchange devices, there is a noticeable difference in AC function. On days between 85 to 95 degrees, I set the temperature to 70 and the car's interior cools down to a comfortable level within about 2 to three miles. On days over 95, I set the AC temperature to 60 and the car cools down in about the 3 to 4 miles. There's no heat soak effect even with multiple trips in 100 plus degree weather, like before. I stopped worrying about overheating for the first time in many summers. If I can park in the shade, it blows cold air almost immediately. Still want to add a later model parallel flow condenser and the other mods I mentioned but this one fix, plus the Koyo seems to have done the trick.
Besides making sure your fan clutch is on point, I would also check the function and condition of the condenser fan, and highly consider upgrading to a higher flow unit. The stock condenser fan is small and lame, like many Japanese sports cars. The one in my old RX-7 was pathetic, and maybe 10 inches in diameter at best. One day, when the AC was getting really chintzy, I looked into the front air intake and saw it just paddling along, like it just didn't care. I replaced it with a Flex-A-Lite pusher fan, and made up a relay harness for it, so it would get 100% voltage. Never had a problem with it again.
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