How much 134a?

[Slant6Demon]

Does anyone know about how much 134a my '72 Demon AC should take? It had factory AC but I installed a Sanden compressor, parallel flow condenser, new hoses, dryer, and expansion valve. The evaporator is original. Also, should I check pressures with windows up, windows down, max AC, regular AC? What vent temperatures should I expect? Thanks.

 

[Demonic]

The rule of thumb is about 80% of the factory charge. You want to simulate max load, so windows down with the fan on high. The goal is about 47* discharge air, but 49-53* will do. Don't forget to remove the EPR valve from the inlet of the compressor if it has one. Sadly they are calibrated for R12.

 

[RustyRatRod]

I never, ever go by any formula or specified amount. I charge until the pressures on the gauges are about where I want them and it cools fine.

 

[Slant6Demon]

Wouldn't the parallel flow condenser have a significantly different volume than the original? 80% of the factory R12 would be about 37oz. That seems like a lot. I didn't know a Sanden compressor would have an EPR valve. Thanks.

 

[RustyRatRod]

Wouldn't the parallel flow condenser have a significantly different volume than the original? 80% of the factory R12 would be about 37oz. That seems like a lot. I didn't know a Sanden compressor would have an EPR valve. Thanks.

Exactly why I prefer to use the gauges and just get the pressures right. Too many variables.

 

[Lefty71]

Exactly why I prefer to use the gauges and just get the pressures right. Too many variables.

I agree, and this is the right way, especially when dealing with non-OEM components..... Some people may need to be reminded to go slowly as you approach your goal tho.

 

[Slant6Demon]

Thanks all. Finally got warm enough to work with AC. These are the numbers at 75 deg ambient, 50% humidity, doors open, fan blowing on condenser, 1600 rpm. 15 psi low, 165 high, 45 deg at vent. Am I under charged? I only put in about 19 oz 134a. The low side seems low, but the vent temp seems ok. How much under charge will harm a Sanden compressor? Thanks.

 

[j par]

I don't think an under charge is going to hurt much as long as it has the correct amount of oil lubricating.. Which it should come with...

 

[TrailBeast]

Thanks all. Finally got warm enough to work with AC. These are the numbers at 75 deg ambient, 50% humidity, doors open, fan blowing on condenser, 1600 rpm. 15 psi low, 165 high, 45 deg at vent. Am I under charged? I only put in about 19 oz 134a. The low side seems low, but the vent temp seems ok. How much under charge will harm a Sanden compressor? Thanks.

My new Classic Auto Air unit takes 24 oz they say.
They also say if the compressor is noisy it’s over filled.
That kinda infers that one can fill until it gets noisy and let a little out.

FYI, I had 40 degree air with the 24oz, but only showed about 20 on the low side and 150 on the high side.
I then added a little more coolant until the low side was
Around 30 lbs and it got noticeably cooler, but the compressor was still quiet.

 

[Demonic]

Definitely undercharged. You could wait till a 98* day and see or maybe add an ounce or two. If the evap hits the unhappy spot where it is 32* or below, the condensate on the coil can freeze, which will block airflow, which will drop suction pressure, etc, etc.

 

[Slant6Demon]

Thanks everyone. Finally got an 80 degree day. Added about 9 more ounces of 134a for a total of about 28 ounces. Low side is 22 and high side is 180. Vent temp is about 43. The static pressure at ambient is about right. I'm pretty sure that the evaporator temperature control switch is cycling the compressor, so it's probably not going to get any colder. The low side still seems low, but I definitely don't want to over charge it. Any thoughts? Or should I admit defeat and have a professional fine tune it?

 

[RustyRatRod]

Thanks everyone. Finally got an 80 degree day. Added about 9 more ounces of 134a for a total of about 28 ounces. Low side is 22 and high side is 180. Vent temp is about 43. The static pressure at ambient is about right. I'm pretty sure that the evaporator temperature control switch is cycling the compressor, so it's probably not going to get any colder. The low side still seems low, but I definitely don't want to over charge it. Any thoughts? Or should I admit defeat and have a professional fine tune it?

I would say that's about spot on.