The aircon in my 1990 NA is dead. AC switch on and the slider all the way at the blue end, and warm air blows out. I've been reading up on R-12 to R-134 conversions and it does not bode well from a financial perspective. I've found an online retailer selling R-12 for $2.42 an ounce*, should I stick with Freon or is the conversion for the 2nd gen RX-7 not terribly involved/expensive?

*I did not realize R-12 required certification to buy.

 

warm air blows out? or just "not cold" air? if warm air is actually blowing out its more likely that either the control unit is fried, or the actual air mix motor itself is dead. both are notorious for failing.

 

By warm air, I mean air the same temp as the cabin. It's a black car and a Michigan summer.

 

try going down the highway or something and see if it changes from full cold to full hot.
my car has the same problem no matter what i do it blows out hot air because the air mix motor is fried and stuck on full heat.

 

R134a: Our 2nd gen RX7's do not convert well to 134a. The condenser capacity is inadequate.

The fuel based R12 substitutes, ES12 Enviro-safe, hotshot, HC12 etc etc have issues. The first and foremost is that they do not work very well. Ignore anyone who says otherwise. I spent years trying commercial versions and even blending my own. When you really need A/C, they just don't have the capacity to move enough heat. Oh yeah, and they are also highly flammable.

Freeze12, a blend, is 80% 134a and 20% 142b. It works great and can be bought without a license. Only trouble is that if you have small leaks, the two refrigerants leak at different rates. Therefore top-offs are to be avoided. Evacuate and charge from scratch. Use 2-12 oz cans charged by liquid into a 29+" vacuum.

R152a is the new refrigerant that is very slightly flammable. It won't self support flame. It has pressures very similar to R12, performance is very acceptable. I have 2 Rx7's and a Toyota Celica Convertible currently running 152a. Use 20 oz of R152a.

R12 is still the king for our FC's. Use 29 oz R12.

Additional Recommendations:

Receiver-Dryer: If you do not know when the dryer was last replaced, replace it the first time you work on the system. The original equip dryers will not stand up to synthetic lubricants such as Ester POE and PAG.

Also a very common problem is getting the correct drier for our cars. There are two different dryers and they do not interchange. Go to a parts store, they are very likely to sell you the wrong one which is a hassle to return. Order one online and you will likely end up owning a dryer that you cannot return. I can help you verify the correct dryer if you need help with the correct part. Just PM me for the help.

Lubricants: Do not use PAG in any car that has ever had R12 in it. Use instead an Ester/POE lubricant. Ester/POE is fine for R12, Freeze12, R134a, R152a.

 

Jack,

Curious... Where would one find r152a?

 

I had a PM question. Can you add Freeze12 to an R12 system without pulling a vacuum?

No. When refrigerants are combined, the result in pressures may be very different from either single refrigerant.

 

If the condenser capacity is inadequate, can it be replaced with a newer one that is more efficient? If one could be found that would fit into the stock location, say from a late model car, would this work? I know that there would be fabrication problems with the lines, but other than that I don't see this as a very hard project to do. Any guide lines on such a project?

 

Actually, I think CordT might have my answer. Last night, My dad and I took Lucy (my car's name) for some...fun, around 11PM. Tried the aircon at freeway speed and it was slightly cool, and judging by the blast of refrigerant I got blown into my face when testing the pressure in the system, there isn't a shortage of ozone-be-gone.

I take it the 'air mix motor' is under the dashboard, correct? I bet that would be fun to replace...What about the control unit? how hard are either components to buy and R&R

 

we've done a couple of R134 conversions, and the high side pressure gets really high. not sure if there is some other mechanical thing that causes it, but some cars seem ok, and we had one actually pop a high side hose!

R12 is actually not that bad cost wise, you only have to buy 2 cans...

 

Great Question! and the answer is yes you can. Here is the exact part you need https://www.ackits.com/pc/24-50003/P...ser+(14+X+19.5)

It takes a little custom work, some other pieces, custom hose work etc. Doing an install with this parallel-flow condenser will enable you to use R134a while obtaining correct pressures and temperatures. This allows any shop to work on the car without the issues brought on by using alternative refrigerants like Freeze12.

Every summer I expect to to this to my car for the next winter, but every summer the car just cools so well on R12 that I leave it alone.



This is why EPA *requires* a high pressure cut out switch on R134a conversions. Cut out happens at 384 psi compressor cuts back in at 256 psi...

Correct switch for our cars:
https://www.ackits.com/pc/57807MD/co...Cut-off+Switch

This is just another way of reducing head pressure/capacity. IOW, reduced cooling.

http://www.epa.gov/ozone/title6/609/justfax.html
Retrofitting Vehicles to Alternative Refrigerants
Although Section 609 of the Act does not govern retrofitting, Section 612 of the Act, which describes the Agency's Significant New Alternatives Policy (SNAP) program, does require that when retrofitting a CFC-12 vehicle for use with another refrigerant, the technician must first extract the CFC-12, must cover the CFC-12 label with a label that indicates the new refrigerant in the system and other information, and must affix new fittings unique to that refrigerant. In addition, if a technician is retrofitting a vehicle to a refrigerant that contains R-22, the technician must ensure that only barrier hoses are used in the A/C system. Finally, if the system includes a pressure relief device, the technician must install a high-pressure compressor shutoff switch to prevent the compressor from increasing pressure until the refrigerant is vented.

 

Bumping in case my Q got forgotten.

Just realized while my little brother was driving to Blockbuster; there is heat radiating from under the dashboard even with the fan off/slider all the way blue. Control unit?