Does anyone have experience with AC on the MK3 Supra Specifically?

[CyFi6]

Well i have been trying to fix my AC forever and haven't been successful. I have had the Professionals here in AZ working on this thing and even after putting almost 1k into parts and labor the thing performs about the same that it did before. It was an R134A conversion, which i was told was not the best refrigerant to use in these cars. I assumed that was my problem and converted back. Here is everything i did:
-New compressor
-New Receiver
-New flexible compressor suction/discharge hoses
-New seals all around
-New TXV
-Professionally flushed (with HECAT equipment)
-----------Evaporator
-----------Condenser
------------All lines
-Added 7oz mineral oil via compressor suction port
-Less than 2 year old OEM turbo fan clutch with 10 blade fan
-Brand new fan shroud
-Dual aux fans added
-Single pusher fan added
-Stock inter cooler, engine under cover in place
-Got all windows tinted
-Heater core completely bypassed

System was evacuated and charged by weight by the pros. Seemed to cool well in their shop when run for awhile and held at 1500 rpm, however taking it into the real world heat of AZ the thing struggles to cool. Initial running of the AC results in warm air for at least a few minutes, after that, its mediocre, about 60-65 out the vents on high recirc for about 15 mins before the temperature gradually comes down and settles about 50-55 depending on driving conditions. On the highway it will come down to 45 at the vents.

Short trips, AC is not worth turning on because it takes so long to get cool, and idle is almost worthless. Have had it in and out of the shop several times and they basically tell me everything checks out and its working as it should. I see claims of people getting vent temps in the 40's in 100+ weather, and i dont see how that is possible. They are either exaggerating or my system isn't working properly.

If you care to read, there's an entire thread on the AC forum about my whole problem, but here are the pressure/temperature readings. It was a 95-100 degree day but i didn't measure ambient 2" in front of the condenser.

http://www.autoacforum.com/messageview.cfm?catid=2&threadid=22263

All with fan on high and in recirc mode with windows open.
This is after running the ac for 10 minutes, after driving about 45mph. I took pressure readings after they stabilized. At 1500 rpm high and low side pressures were slowly roaming up and down about 10-15 psi.
Idle:
High: 350 psi Low: 50 psi
Vent temp: 65 deg F
Suction line warm

1500 RPM (hood open for this one to hold idle up)
High: 325 psi Low: 25 psi
Vent temp: 55 deg f
Suction line barely cool

My question to you is, does the AC on these cars just suck or is there actually something wrong with my system?
Thanks.

 

[Nick M]

The high is too high, even for your heat. But your discharge is not bad considering the heat. Strange that 25 psi (25 degrees) does not feel cold to you.

The performance test is not done in recirc mode. It is done in normal mode, otherwise you will not know how good or not good the system is. 325 and 25 seems like a high side restriction, like the compressor itself. But 50 on the low side doesn't equal a high side restriction. Who did the TXV? If the evaporator isn't done right with the TXV, it can hang open. One other thing, just how much refridgerant is in it?

 

[te72]

I had the a/c in my 88 recharged in April 2006 (in AZ) for the summer. It got pretty damn cold for April, had the windows tinted the same time. Only lasted a few months, but I spent them in Wyoming, so it wasn't all that necessary. In AZ summer heat, I've never been in a car that felt *all* that pleasant during the day, in the ~12 years I lived in Phoenix.

 

[90T04]

I agree that your high side pressure is too high. One thing you might look into is upgrading to a parallel flow condenser. The system was designed for R12 and I wouldn't blame it for not working at 100% with R134A. Especially in AZ! With a more efficient condenser you might get those high side pressures down and get a bit better cooling.

 

[Poodles]

I agree that your high side pressure is too high. One thing you might look into is upgrading to a parallel flow condenser. The system was designed for R12 and I wouldn't blame it for not working at 100% with R134A. Especially in AZ! With a more efficient condenser you might get those high side pressures down and get a bit better cooling.

Well i have been trying to fix my AC forever and haven't been successful. I have had the Professionals here in AZ working on this thing and even after putting almost 1k into parts and labor the thing performs about the same that it did before. It was an R134A conversion, which i was told was not the best refrigerant to use in these cars. I assumed that was my problem and converted back.

 

[metaphysico]

First off as everyone has said high side pressures are too high, and low side are too low. The two main causes for this are restriction on high side or TXV sticking. As for r12 vs 134A I am a little on the fence from most people on this one. There is not a large difference in the temps you can get. Now that being said charging with r12 and 134a is different in the effect that r12 is lighter than 134 so you need to add less 134 than you would with r12. I think this is where a lot of people see the difference in cooling they add too much 134a. The conversion is around 90% to 95% 134a compared to r12. Now I did a retro on my supra, well kind of, I just put retro fittings on it and charged it. The compressor was off the car when I got it so there was nothing in the system. This is not the normal way I would go about doing it but to my surprise it lasted 5 years before running low on freon due to an unfound (haven't looked for it yet) leak.

So back to the problem at hand, with the temperatures you have you have a restriction in the high side, and a sticking close TXV is a restriction by all definitions. So the thing to do now is to find the restriction. Now this can be limited down some because the high side pressure port is on the liquid line so from the compressor to the condenser should be ok, and the condenser itself should be ok. The reason I am ruling these things out is because if there is a restriction before the port then your pressures will be low not high. So it has to be after the port. Now after the port there is a liquid line to the dryer, the dryer, the liquid line to the firewall then through the TXV.

Now with all this in mine we have limited to where the problem can be, so you need to check to see where the restriction is. The way to tell is the high pressure liquid is hot/warm, after the restriction it will be able to expand and cool off. The easiest way to test is if you have a laser thermometer (I saw radio shack has them for $20 for a cheep low temp one, something like 300 degrees max), but before you buy one you can test it by hand. There will be a noticeable temperature drop after the restriction. So run your hand along the liquid line and check for any drop in temperature, the dryer will have some drop but not a drastic if its ok. Then there is not a large drop in temp anywhere then it will be a bad TXV I have gotten thermal expansion valves that were stuck closed or would not fully open more than a few times. Also if they did not do a good job getting all of the flush out of the system it can screw up the TXV. A normal problem with restrictions and getting these kind of temperatures is a clogged fixed orifice tube, but I have not found one on a mk3 so I am guessing they don't use one.

Last note, with a outside temp of say 100 degrees and low humidity ie AZ, you should be somewhere between 250 and 300 psi on the high and around 40-50 on the low both at idle. Low side should be down to 30 at 3k rpm and high pushing 300.

 

[90T04]

Doh! I missed that.

One other thing, just how much refridgerant is in it?

 

[Poodles]

As your car doesn't look like an 89 in your sig I can't say that the expansion valve issue effects your car. IIRC, they had an issue with the expansion valves causing too much high side pressure and were replaced on a case by case basis at the dealer (hence why i have one sitting here on the shelf whenever I redo my A/C system).

 

[Satan]

...couple of suggestions.... 7oz of mineral oil sounds kinda "too much," but I can't remember how much I used for the 2J compressor I am using (I have a 2J swap). I replaced my condensor with a "parallel flow" designed one and feel that this is a must for our MKIIIs... I've had 3 other MKIIIs w/R134 conversion and never was satisfied with the A/C performance. Very satisfied with it now...

Suggest you do your own work and learn the system, so that U can save some $$.... I had not done A/C before this conversion, but used this thread (and a couple of others) as a guide....

http://www.supramania.com/forums/showthread.php?t=44138

Good luck!!

 

[CyFi6]

I have checked for a high side restriction already, i will check again though. This vehicle has had 3 different TXV's in it and with all of them, the pressures have been nearly the same with no increase in AC performance.

Satan, I filled the compressor with 8oz originally as per a Napa created spreadsheet for AC system capacities. The TSRM does not give an exact amount for oil, they only give amounts for each component to be replaced, which doesn't include any lines. The AC place thought i may have too much oil, and removed an ounce, which didn't help very much. Also, i do all my own work that is within my capabilities. The only work i did not do was the flushing and charging of the system, because it is impossible to properly charge a system without a refrigerant scale which i don't have.

The system was charged by them, so i don't know the exact amount charged, but it was most likely done to specs.

 

[Satan]

...I'd suggest you get a newer desingend condensor over the Winter and refill/recharge in the Spring. I had the other 3 conversions done professionally and only had nominal performance. I had a thread w/the results of the one I did myself... I'll see if I can find it.

 

[grimreaper]

^ Either that or go back to R12. isn't mineral oil for r12 anyway The correct oil is needed. The way the system oils it self depends on it!!
Your High side PSI looks high but I dont have the r12-r134 psi conversion stuff anymore. I know the pressure will be higher with r134 just cant recall whats expected..
I'd give the parallel flow condenser a shot. Full evac and find a shop that charges by weight. Most do but sometimes you'll get hank hill in the back doing it old school with pressure.

I agree your vent temps have some room for improvement. Just keep in mind simple things like facing the sun or black top vs concrete parking lots will have a small affect on things once you get the system working optimal. Dont go ape shit over a few degrees once you get to that point.

 

[CyFi6]

Maybe i wasn't clear enough, but the system used to be R134A, i converted the system back to R12 and it is now R12. Before i start trying to upgrade the system I really just want to know whether or not there is something wrong with it. Trust me I would be happy if the thing blew 50 degrees all the time, but when i jump in my car to drive home and it sits there at 65-70 degree vent temps for the first 10 minutes of driving its a little frustrating.

I checked all along the high pressure line, by the way, and no cool spots were found, the line was hot all the way from the receiver to the firewall.

 

[Nick M]

I have checked for a high side restriction already, i will check again though. This vehicle has had 3 different TXV's in it and with all of them, the pressures have been nearly the same with no increase in AC performance.

That doesn't change the fact that the TXV could be installed wrong. If the sensing bulb isn't sensing cooling, it will hang open. That could be making your high to high.

 

[CyFi6]

I installed the TXV myself, and the sensing bulb is clamped tightly to the stock location on the suction line and properly covered with the foam packing material. Besides, wouldn't a txv that is open more than it should be cause a drop in high side pressure?

 

[3p141592654]

Yes it would.

Both your hi and lo numbers are too high for R12 at 1500rpm. Common problems would be an overcharge, inefficient condenser, or air in the system. How long did you pump out this system. Are you using the correct drier for R12?

Not much data here. Go back and compute superheat and subcooling for the two conditions. That will allow you to focus on where the problem really is. You should be seeing 3-5 deg subcooling.

By the way, a hi-side obstruction will result in low lo-side pressure, so stop wasting your time looking for one.

 

[89supracrazy]

I had the same problem with mine when I got on the 4 lane it would get colder and in town it was not cold. I found that the ac setup had three relays and one was missing. So I bridged the connector that the relay was missing and it runs all the time. It was the condenser fan was not running at all so the faster I went it circulated more air threw the condenser. It works fine now. I believe I read where you added a fan right. I agree with those pressure too much refrigerant or blockage in the system.