AC temp?

[Nick Triesch]

I redid my original AC a few years ago and just started driving my 85 black on black 911 again because I have been sick. I topped off the refrigerant and I’m getting 60 degrees at the vents with an outside temp of 87. Does my car temp seem about right for year or should it be lower? Thanks,, Nick

[dw1]

After a few minutes of AC operating on high in my black/black '87 I get vent temps in the low 50's with an outside air temperature of mid-80s and rh 50-60%. After a longer time, I can get high 40s. FYI, my system has the stock evaporator and condensers, and recently replaced barrier hoses, a new evaporator valve, and a rebuilt compressor.

So, yes IMHO your AC should be a bit better, but don't expect too much better from a stock system even if it is in the best of condition, and our cars (and their AC system components) are getting old.

If you want good AC in these cars, check out the enhancements from Griffiths Technical.

[Nick Triesch]

Yes, my car has old hoses , rebuilt compressor, other stock stuff . New thermostat , dryer, expansion valve, Closed windows, started ac in garage . 60 is what I get. Yes, car and system is old. Thanks

[Nick Triesch]

So your system is not that much different than mine. I will keep trying.

[dw1]

One thing to try - when charging the AC, vacuum it down for a long time, let it sit closed for a few hours under vacuum, then vacuum it down again for a long time. This helped my system and might help yours.

Most AC recharge instructions assume far shorter hose lengths and thus far less surface area than is in our rear-engined cars. Vacuum procedures, as well as refrigerant amount, needs to compensate.

[Nick Triesch]

Ok, thanks!!

[Coastr]

Try spraying the condenser with water through the grill when it’s running and see if you get temp drop. If you do then you it’s working ok just doesn’t have enough condenser efficiency. If it doesn’t change maybe you have issues somewhere else like evap blocked with gunk or leaking cool air out of a duct or something.

[GH85Carrera]

Box stock AC from the factory is just pitiful. I worked on my system when stock, and it was OK at night, in the rain or when the OAT was below 90. Above 90, it was almost better to open the windows.

Like dw1 above said, pull a longer vacuum. You truly can't get too good of a vacuum, it is not possible.

I have the Griffith's 4 condenser system, and I get cold air. My vacuum process is something I describe as belts and suspenders with glue, overkill maximum vacuum.

I set up the vacuum pump and let it run for two hours, at least, I use a micron gauge to get an true accurate measurement of the vacuum. I let that sit overnight as is. The reading is almost always higher in the morning. I theorize there is water converted to ice in the vacuum, and it takes a long time for it to sublimate into vapor.

The next morning, I purge the system with nitrogen and pressurize to 100 PSI or so, and then check every fitting and connection I can access with soapy water to look for bubbles. If none are found, I pull a second vacuum for at least an hour and I have not removed a single hose, to possibly add air.

Then I do a second nitrogen purge, to 100 PSI, and then change the oil on my vacuum pump to new oil, and pull a two hour minimum vacuum pull. I want to see the micron gauge stop going down, so I know I have the most vacuum my pump can manage.

Then and only then do I add refrigerant.

A nitrogen purge rig is likely something you can rent, but I just bought mine. The micron gauge is not vital, but a nice tool to know what level of vacuum you have. The standard gauges just can't display the really low levels.

No pro anywhere would do all of that, so I just got my own rig.

[ahh911]

81 911sc usa.

Stock york compressor, stock condenser (one in back one with fan up front), orig evap unit and fan, original drier.

Cleaned, de-carbonned the fan's internals over winter. Both evap and condenser run quiet and smooth as a modern car.

A/C was completely empty/no residual pressure at all and most likely not used in several years, though the prior owner told me it worked.

1. Removed existing oil from compressor sump and added 6oz of Supercool brand ester oil with dye.
2. Used the oil vacuum extractor (Mityvac) to achieve between -25 and -28 inHg, depends on the gauge used and checked that it held vacuum to a fair amount over several days.
3. Pulled the vacuum again.
4. Started car air bypass screw set to ~2000rpm and added to low side, back lid down most of the way, monitored high/low side pressure
5. 9oz bottle of utlracool r12a with lubcricant and dye written on the product. Car would cool.
6. By weight it wasn't enough, so re-checked pressures the next day, make sure the gauge valves are closed, 6oz bottle of ultracool r12a added, pressures were good, by weight was good, in the drier window you can just see at the bottom a little bit of fluid, i.e. the sight glass is over 99% empty, and you just see some fluid running at the absolute bottom of the glass, then it pulls back down below. (function of refrigerant, my experience only, info says to fill by weight and pressures and ignore the sight glass).

Closed up. 3 weeks later:

Conditions:
86F today (30C), humidity 45%, 25 minute drive in the sun.
Range vent temp: (3.5-10C) 38F to 50F. Driving vs stop light.
Average cruising temp at 2500-3500rpm, (5.5C) 42F.
Fan setting 2 (one below max, it makes a difference.).

Questions, I'll answer if I can.
Works better than my 2003 bmw and vw passat, and the cold will burn up your chest if vent directed at you, cabin seems cold enough, but don't wear jeans cause it isn't that cool

Phil



4.

[dw1]

Originally Posted by Coastr

Try spraying the condenser with water through the grill when it’s running and see if you get temp drop. If you do then you it’s working ok just doesn’t have enough condenser efficiency. If it doesn’t change maybe you have issues somewhere else like evap blocked with gunk or leaking cool air out of a duct or something.

Very good point. When working on my system last fall I found some vent tubes in REALLY bad shape. Check this out: https://forums.pelicanparts.com/11455840-post9612.html

[Nick Triesch]

I also noticed that when the ac fan is one click lower than high, I get lower temps. Weird.

[911obgyn]

More time for the air to cool over the fins, heat transfer.

[Nick Triesch]

All I know is my 85 has the world’s smallest front AC vents and the side vents are like from a cartoon! And little vent underneath by your leg. Yet Porsche installed 12 fans for heat!!!!! What a crack up. I love my car.

[Nick Triesch]

I just went out and put in more 134a in my 85 911 , and went for a drive. At 82 degrees outside I got 47 at the vents. But I need new Barrier hoses. Due to health issues I can’t change them myself if I bought the hoses , how much do you think a shop would charge me to install them. Then I would do all the other stuff like vacuum and charge system.

[Nick Triesch]

Never mind. I had no idea the hoses cost that much! The Wife wants granite countertops! Hoses must wait.

[ahh911]

Originally Posted by Nick Triesch

All I know is my 85 has the world’s smallest front AC vents and the side vents are like from a cartoon! And little vent underneath by your leg. Yet Porsche installed 12 fans for heat!!!!! What a crack up. I love my car.

Didn't realize those little vents were for a/c. Turned them appropriately today and they cool the outer arm off nicely. Humidity is up to 70% didn't notice any drop in vent temp.

[Coastr]

Results further up with the stock system is running r12. With everything in good order and running r12 it will get cold. All the ‘it never worked’ comments are from neglected systems r134 converted. R12 is just better but is outright banned in many places. R134 with new hoses and compressor will work - to get great results you also need extra condenser.

[schoward]

I have vent temps in 30s and 40s routinely each year in my SC with a stock system that was converted to R134A with new compressor, dryer and the original condensers removed and flushed. Shops say I got lucky with these results which indicates people can experience a range of outcomes. Now the airflow is lame so its not like a modern car but it can get me by ok when I need it. This is starting out with car in garage at normal ambient temps.

So - good chance you can get better results. Make sure front condenser fan is working. Do not overfill refrigerant. I fill mine each spring as I do not have barrier hoses and exactly 2 of the normal short cans (12 oz. each I think) is the magic number each year.

Also keep in mind - If you are letting a black dash bake in the sun for hours and then expect cold vent temps, probably wont happen. The stock fan airflow often cannot overcome the oven that the car becomes sitting in the sun. If were to let mine sit for hours in the sun, I would not get results above.

[Nick Triesch]

I got dash temps down to 42 degrees on my stock A
C on a warm San Diego day. Not bad for black car! My point is if you ever sell your car and want the AC to work it’s just not that hard. Cost me a total of $595 to make it work. Bought gauges and pump, Dryer, expansion valve, thermostat, Oil and refrigerant, compressor rebuilt on eBay . Works well but not after 90.

[dw1]

Nick - Good Work!

I'm happy to hear that you got your '85 black car's "stock" A/C working about as well (if not slightly better) as my '87 black car's "stock" A/C.

As I recall from being stationed at NS San Diego (about a million years ago) it didn't get above 90 all that often.

It seems that the differences between your car's A/C and mine are that I have barrier hoses (which help to avoid refrigerant loss over time) and I rebuilt the compressor myself (using Griffiths' kit and very helpful instructions). I also recall that in MY1986, the vents were revised.

In recent days, I also installed a PWM controller for the evaporator fan more or less per our sponsor's "how to" article (https://www.pelicanparts.com/techarticles/911_ac_switch/911_ac_switch.htm) and while it does make things a bit better, I have my doubts whether it was worth the effort.

I also decided to make a custom passenger-side floor board so I could mount a 12v fan (a 80mm PC case fan I had sitting around) to take in air from behind the console into the area under the floor board and indirectly into the evaporator inlet duct. Based on vent flow measurements, this actually does help - not a lot, but some.