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HC R12a in the stock 968 AC system - Printable Version

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HC R12a in the stock 968 AC system - 968 Cab - 07-27-2005

UPDATE – measured the Vent Temps today - follow up on Dave Greimann's post http://www.968forums.com/index.php?showtopic=905



Conditions

• Warm sunny day

• In garage – 968 readout = 78F

• In sun – 968 readout = 93F



Finally got hold of a thermometer and DS taped it to the center vent to check the temperatures after the HC R12a charge. I decided not to change the OEM receiver dryer as it appeared that it was recently changed. So basically my system was OEM but completely dry (drained by the dealer during service!) System was checked for leaks by a local AC outfit (they used liquid nitrogen to check) – no leaks. So I added 3.5 oz of EnviroSafe Oil Charge and proceeded to fill with 11.5 oz of ES R12a (takes 1/3 of the old R12 fill).



When the car was first driven, the compressor made a racket but now it has quieted down completely – Greimann suspects the lower volume of R12a fill resulted in a little cavitation at start up. and I agree But after driving for 20 miles, it gradually returned to normal.



Here are the temperatures I recorded today (sorry for the fuzzy photos – not easy to focus, shoot and drive!)



Photo # / Temp Reading / Fan Setting / Notes



#1 / 75F / fan off / parked in the garage before starting up

#2 / 53F / fan #4 / 1 min after starting the car – blowing cold air

#3 / 53F / fan #1 / 2 min after start up – driving maintained 53F temp

#4 / 48F / fan #3 / 5 min after start up – driving

#5 / 45F / fan #2 / 6 min after start up – driving



Couple of observations –



• HC R12a works.

• The coldest I recorded was 43F on fan setting #2.

• It was easy to maintain the temp when the car was hot, in motion, etc.

• Fan setting #3 or 4 worked fine to cool the car when it was “cold” but as the car warmed up, the AC output temp climbed a few degrees unless I turned the fan down to 1 or 2. I think the evaporator was freezing up a little at the higher fan speeds.



All in all, a good product so far – easy to use and it works (but make sure there is good ventilation or you’ll end up with a massive headache during the filling with the minute amounts of gas that escape when removing the hoses).



Hope this helps some of the owners thinking of a DIY solution. Best thing, no need to pull a vacuum as the R12a does not require it. Search eBay R12a for online suppliers.

HC R12a in the stock 968 AC system - Greimann - 07-27-2005

Great follow-up! I'm glad someone else has had success.



Your increase in temperature at higher fan speed would be expected. Since the evaporator will ultimately reach a minimum, stable temperature, a higher fan speed will draw a larger volume of warm air through the system than the evaporator has the ability to cool to the temps you see at lower fan speeds. You will get more cooling BTU's at higher fans speed, even if the vent temp is a bit warmer.



When the evaporator freezes on my truck the air flow pretty much stops coming out of the vents. You have to turn off the compressor so the block of ice can melt and open up the plenum again. My 968 doesn't have that prroblem.



I would like to see a follow-up on your experience with this set of circumstances: Driving for at least 30 minutes with the AC on, do you notice a significant increase in vent temperature at a stop light?

HC R12a in the stock 968 AC system - 968gene - 07-27-2005

Dave, Do you have the correct amount of gas/liquid in the system? I'm reminded of a system that was low on R12 that would freeze.

HC R12a in the stock 968 AC system - Greimann - 07-27-2005

[quote name='968gene' date='Jul 27 2005, 07:43 PM']Dave, Do you have the correct amount of gas/liquid in the system?  I'm reminded of a system that was low on R12 that would freeze.

[right][post="8036"]<{POST_SNAPBACK}>[/post][/right][/quote]

The thing about hydrocarbon refrigerants is that you only use about 1/3 as much as the "normal" refrigerant. This can be an issue at low ambient temps in a system with a high pressure cut out like my Chevy truck. The pressure never gets high enough to cut the compressor off.



The 968 has a thermostatic expansion valve and can regulate the evaporator temperature independent of system pressure, so the Porch shouldn't freeze.

HC R12a in the stock 968 AC system - 968 Cab - 07-28-2005

[quote name='Greimann' date='Jul 27 2005, 06:55 PM']Your increase in temperature at higher fan speed would be expected. Since the evaporator will ultimately reach a minimum, stable temperature, a higher fan speed will draw a larger volume of warm air through the system than the evaporator has the ability to cool to the temps you see at lower fan speeds. You will get more cooling BTU's at higher fans speed, even if the vent temp is a bit warmer.



I would like to see a follow-up on your experience with this set of circumstances: Driving for at least 30 minutes with the AC on, do you notice a significant increase in vent temperature at a stop light?

[right][post="8032"]<{POST_SNAPBACK}>[/post][/right][/quote]



ahhh, so all is revealed! Thanks for the heads up Dave. I'll do the longer drive and check out the temps and then post a follow up. All I know is that the system works really well again, and with the top down today, I was getting nice cold air in the car while the sun was shining - even when stopped at a light. No more baking in the sun when the traffic comes to a crawl!

HC R12a in the stock 968 AC system - 968 Cab - 07-28-2005

[quote name='Greimann' date='Jul 27 2005, 06:55 PM']I would like to see a follow-up on your experience with this set of circumstances: Driving for at least 30 minutes with the AC on, do you notice a significant increase in vent temperature at a stop light?

[right][post="8032"]<{POST_SNAPBACK}>[/post][/right][/quote]



Sunny day 85F, top down and dash center vent reading is as low as 40F at fan #1 and min temp on the dial! So it all works really well. Compressor is nice and quiet too. Opening the floor vents and a higher fan speed causes a slight temp increase to 44-46F on the thermometer. Ahhh, lots of nice cool air flow at the traffic lights now. <img src="/forum/images/smilies/968/laugh.gif" class="smilie" alt="" /> no more hot smelly feet <img src="/forum/images/smilies/968/rolleyes.gif" class="smilie" alt="" />



This photo is after 45 min drive, sunny day 85F outside. Fan setting #1 Temp sticks at 42F whether stopped or moving now. Only goes up a few degrees to 48F when fan speed is increased up to #4.

HC R12a in the stock 968 AC system - Greimann - 07-28-2005

I think we have a believer! Good deal [Image: 2thumbs.gif]