New compressor - A/C Not functioning

[David T]

Your numbers (amount of -134 and gauge pressures) do not make sense. Could be because of your variable displacement compressor. When converting to -134 you can only use about 80% of the fill you would use for R-12. Even at that, pressures will be higher than if you are using -12. Because the cooling capacity is based on the mass (amount) of refrigerant, your cooling capacity is reduced by about 20% when you use -134. Lock the compressor up at full tilt, remove some of the -134, check your pressures at 1,000 RPM. You should get a 20 degree temperature drop at the vents. Make sure you are in recirc mode and you don't have any large leaks into your doors.

[FABombjoy]

But since your idle is only 650 RPM that could account for lower high side pressure at idle.

Fair point - I was assuming the pulley sizes were scaled for the lower LS motor idle.

The gauges could potentially be of issue, they are cheap ones from HF.

Haha, I understand completely. Both Andrew and I have the same gauges here and they seem to get the job done. If they equalize when off then they're probably fine. Seems unlikely that both would be off scale but retain a common crossover point.

[Nicholas R]

After running your crazy yankee numbers through the computer, that is only 1.6lbs? Why so little. I will certainly try it however I am curious. It would make sense that the system is overcharged, however the pressures seem OK to me too.

How much refrigerant to use has been a question I've had as well. I've read everything from use "80% of the R12 amount", to "use 95% of the R12 amount", to "Use 100% of R12 amount." At this point I'm more confused than anything.

Admittedly, 24oz/1.5lb/68% of stock seems a bit low.

[Delorean Industries]

Nothing to be confused about:

Factory r-12 charge 2.5 lbs
Conversion rate of r-12 to r 134 via Dupont = 2.00 pounds of refrigerant required on stock size system.

DPI line kit has smaller ID compared to stock thanks to superior barrier protection and permeation qualities. This means the system is more efficient and has less of heat loss coefficient compared to stock lines (less refrigerant required to get job done). Standard charge 30 ounces depending on accumulator style installed. (this can vary down to 28 ounces.

Hervey evaporator core has a total volume of 71% of stock evap core. This reduces the ability to boil and transfer heat through the refrigerant exponentially. Too much refrigerant causes the evap core to freeze and loose efficiency. This is why your low side is bottoming around 30. In all actuality is is probably a lot worse. Gauge quality is a major factor.

This lands us at a system requiring 24 oz's in this situation.

I have filled and tested every combination possible here as some owners have done there own work in the past and forced us to deal with undersized condensers and evap cores. Hence finding the magic numbers.

[Nicholas R]

Nothing to be confused about:

Factory r-12 charge 2.5 lbs
Conversion rate of r-12 to r 134 via Dupont = 2.00 pounds of refrigerant required on stock size system.

DPI line kit has smaller ID compared to stock thanks to superior barrier protection and permeation qualities. This means the system is more efficient and has less of heat loss coefficient compared to stock lines (less refrigerant required to get job done). Standard charge 30 ounces depending on accumulator style installed. (this can vary down to 28 ounces.

Hervey evaporator core has a total volume of 71% of stock evap core. This reduces the ability to boil and transfer heat through the refrigerant exponentially. Too much refrigerant causes the evap core to freeze and loose efficiency. This is why your low side is bottoming around 30. In all actuality is is probably a lot worse. Gauge quality is a major factor.

This lands us at a system requiring 24 oz's in this situation.

I have filled and tested every combination possible here as some owners have done there own work in the past and forced us to deal with undersized condensers and evap cores. Hence finding the magic numbers.

I suppose that makes sense. Do you have any information regarding if you're using Hervey's lines? As I understand, his lines are actually larger in both ID and OD than stock. I've always wondered if this warranted an increase in refrigerant use

By the way, isn't the stock charge 2.2 lb? This is another thing that has me confused because the Service Manual states that the charge is 2.5lbs of R12, but service bulliten ST-29-11-81 says that the new amount is 2.2lbs of R12, and that it's a correction from 2.75lbs of R12. What??


Service Manual.pdf
DUZaQMZ.jpg

ST-29-11-81.pdf
yrA18ID.jpg

[Delorean Industries]

Yes there are three different advised charge amounts. Really the only way to figure it out would be to build a completely stock system and fill with r12. Kinda a mute point but it would still be interesting to know which rated charge performed the best. All of our efforts have revolved around using a common refrigerant that is easily sourced. R134 was the obvious choice to use as our standard in house instead of r12.

On hervey lines the only way to find out is to measure the id and calculate the volume differentiation. Volume plays a part but obviously the above mentioned coefficients of heat transfer and permeation play a major roll in the equation as well.

[DMC-81]

By the way, isn't the stock charge 2.2 lb? This is another thing that has me confused because the Service Manual states that the charge is 2.5lbs of R12, but service bulliten ST-29-11-81 says that the new amount is 2.2lbs of R12, and that it's a correction from 2.75lbs of R12. What??


Service Manual.pdf
DUZaQMZ.jpg

ST-29-11-81.pdf
yrA18ID.jpg

I used the 2.2 lbs figure from the service bulletin as from the explanation of the change, it seemed like 2.75 was too much and was causing knocking sounds. I also understand that R12 is more tolerant to a less-than-accurate charge (under filling).

[David T]

2.2 lbs is the newest spec for R-12. Down from 2.75. To use -134 you must use 80% or less to prevent popping the safety valve. That would be 1.75 lbs. R-12 is more tolerant of over or under charging. With -134 you must be accurate. Refer to ST-29-11/81 but that is ONLY for R-12.