Help with A/C. What to do?


My 88 Cadillac DeVille has always kept me cold since I purchased the car last fall. Today was an extremely hot day, and I haven’t driven the DeVille in nearly a month. The temp outside was 106, and the A/C never really got cold. I drove about three or four miles in town … sorta cool but not cold. I am wondering if this is typical for an older Caddy on such a hot day, or perhaps I should try adding some R134? If so, where to buy? What do I need?

If I add the R134, can I do this myself? How would I do so safely? I have heard that the A/C recharging can be tricky and dangerous if you don’t know what you are doing … and I don’t! (-: Thanks


Unless you have had the A/C converted your car’s A/C system still uses R-12. It sounds like you need a charge but I do not think you will find R-12 anywhere. R-134 is incompatible so you will need to convert your A/C system first and then recharge it. You may also have a leak that will need to be addressed before you can recharge the system. Good luck, this one’s gonna hurt.


R-12 is readily available, I just had my wife’s 82 recharged. It’s become a tad expensive ( I just paid about $60/pond). In theory, you need a license to buy it yourself, but there seem to be a lot of folks selling it on ebay. Find a good AC shop.


My car has been converted to R134. Thanks


That makes it easier, you probably have a leak someplace in the system. Have the leak fixed and recharge the system. You could try just charging it, but it was low for a reason.


R-134A conversions are notorious for not getting cold in extreme heat. This is due to R-134a not being as efficient as R-12. If the pressures are correct, then this is the best the system can give you. Adding more R-134a will not help.


Good point, I was assuming the system was low. The system pressures do need to be checked before adding any R-134a. If you are going to do it yourself, you need to buy a low pressure gauge and check the pressure first.

I agree that R-134a conversions can be weak, I converted one system and ended up converting it back to R-12, also the R-134a runs at higher pressures, which can be harder on compressors that were designed for R-12.


Actually, what you should invest in if you want to mess around with A/C is a set of gauges. You can buy a cheap set from Harbor Freight (40 bucks or so?) and they should last a lifetime.
With gauges you get both the high and low side readings and this can tell you a lot about what’s going on inside the system.
They’re also a lot safer as some of those charging hose setups are cheap plastic and anything can happen.
If you use a charging hose then use a brass one.

Since your car has been converted, and obviously has a leak, the usual suspect is the compressor shaft seal but you might consider checking what I assume are conversion fittings? Remove the caps and apply a 50/50 solution of water/dishwashing detergent around and on the fittings. Note if you see any bubbles.

The easiest option for you is to simply add a can of refrigerant and hope this lasts through the summer. Make sure you connect the charging hose to the low side if you do this and you should be able to stay out of trouble. The high and low side should have different size fittings.
Do this in the shade (it affects condenser pressure and temps) and elevate the rpms to about 1500 when doing this.
WEAR goggles and preferably gloves since you’re an amateur on A/C work.
Opened refrigerant will freeze anything instantly if it makes contact.

Personally, I don’t have a problem with R134 cooling and have no problem getting just as good if not better temperature drops than R12. It’s only a problem if allowed to be.


Do this test, it will determine if you really need to charge any refrigerant into the system.

Put the car in the shade when it’s as closer to 80?F as is feasable in your area. Start the engine and turn the A/C to max with the blower on high and all the windows open. Open the hood and observe the compressor. The clutch on the front cycles on and off depending on evaporator pressure (which is almost directly proportional to temperature) but if the system charge is low it will cycle excessively. Start a timer and observe how many times the compressor cycles in one minute; start the timer when you see the clutch engage. Then, use a garden hose to spray down the condensor, and do the test again. If it cycles more than eight times per minute during either test, charge one of those small cans of r134a into the system. Use just plain old R134a (such as a generic brand or Dupont’s Suva), no leak sealers or conditioners. Run the test again, and if the cycle rate is beyond 8/min again, then charge another can. Then feel the pipes leading in and out of the evaporator (at the dash), as close to the dash as you can. If the inlet (the smaller pipe) is colder than the outlet, add one more can, and you’re done. That’s the best you can do. If the outlet is colder than the inlet, then don’t add any more refrigerant. Note that on a converted system this cold, the best you’re going to see is a 35-45?F drop over the ambient air temp. So if the outside air is 106?F, you may only see around 70?F coming out the vent (you can use a thermometer stuck in the center vent outlet to test.) And you won’t see the output temp get colder than 40?F hardly ever.

And even then, expect this performance at or above 30mph, never at idle.

If the system gets and stays cold and doesn’t lose its cooling ability for a while (a while being at least a year) then you in fact actually DON’T have a leak, you merely have lost the charge over time (leak rates lower than 1/2lb a year are acceptable for R134a systems.) Modern systems have smaller charge levels and so are especially sensitive to loss of refrigerant. As long as you never allow the system to get below 30psi (when it’s shut off) (you should definitely invest in a gauge, preferably a manifold gauge set, if you want keep your A/C in check yourself) then you should never have a problem with just adding refrigerant when the system is low because no air will be able to get in. If you have a leak that requires charging more than one small can per year though, be nice to the environment and have the leak found and fixed. You could do yourself a favor by making one of those cans you charge into the system a refrigerant that contains UV Leak Detector Dye (Prestone and Dupont make this available in 12oz small cans with no other additives) that way if you have a leak, it will show up.

Hope that helps!



There has been more than one report that the stuff sold on E-bay is not really the right stuff.