New compressor - A/C Not functioning

[Josh]

Hey guys, looking for some help with my A/C system.

My car has a LS4 V8 and the A/C has always given me trouble.

The A/C system was all replaced 2 years ago.
-New lines from DPI (Eaton EZ clip)
-New 134a condenser from DMC
-New evaporator, dryer, and orifice tube from Special T

I was also using the stock LS4 A/C compressor, which gave me sub-par cooling due to the fact it is a variable displacement unit, which was unknown to me when I originally installed it.
I switched it out to a Sanden sd7h15 compressor, the same that is used as a replacement in the stock delorean. The only difference for my application is it has a 7-rib pulley and a different back plate.
Link to the new compressor: https://www.summitracing.com/int/parts/vta-04709-vma/overview/
My thinking was that I now have an all stock system, so it should cool as well as stock.

However after charging it up yesterday the A/C is worse. It is pretty much non existent in terms of temperature.
The compressor clutch still engages, so the wiring is not an issue.

Any ideas?

[FABombjoy]

That compressor should be lovely - I have the 4708C clone. What do your manifold gauges read?

[Nicholas R]

Hey guys, looking for some help with my A/C system.

My car has a LS4 V8 and the A/C has always given me trouble.

The A/C system was all replaced 2 years ago.
-New lines from DPI (Eaton EZ clip)
-New 134a condenser from DMC
-New evaporator, dryer, and orifice tube from Special T

I was also using the stock LS4 A/C compressor, which gave me sub-par cooling due to the fact it is a variable displacement unit, which was unknown to me when I originally installed it.
I switched it out to a Sanden sd7h15 compressor, the same that is used as a replacement in the stock delorean. The only difference for my application is it has a 7-rib pulley and a different back plate.
Link to the new compressor: https://www.summitracing.com/int/parts/vta-04709-vma/overview/
My thinking was that I now have an all stock system, so it should cool as well as stock.

However after charging it up yesterday the A/C is worse. It is pretty much non existent in terms of temperature.
The compressor clutch still engages, so the wiring is not an issue.

Any ideas?

My understanding is that you can make the variable compressors fixed by modifying the refrigerant control valve. I never gave much though to this though. I'm not sure I understand why the variable displacement is worse.
56406

This is odd though that you're not getting any cooling at all. Even last week when I was running with my trashed compressor, I was getting ~55° air from the vents. You're sure you put the orifice tube in the correct direction right? Do you still have the heater fluid shutoff valve active? I always notice a difference between "Normal" and "Max" AC in my car primarily due to the heater not circulating fluid during "Max".

[Josh]

That compressor should be lovely - I have the 4708C clone. What do your manifold gauges read?

At idle (650rpm)

Low side - 32psi
High side - 150psi

Ambient temp was about 80F
Charged with 2.2lbs 134a

[Josh]

My understanding is that you can make the variable compressors fixed by modifying the refrigerant control valve. I never gave much though to this though. I'm not sure I understand why the variable displacement is worse.
56406

I never even knew this was a thing. This may be a back up plan. Thanks Nick!

[Delorean Industries]

At idle (650rpm)

Low side - 32psi
High side - 150psi

Ambient temp was about 80F
Charged with 2.2lbs 134a

Too much refrigerant in the system. You need to back the refrigerant down to 24oz with your configuration (two cans) This is from taking into account the parts list supplied above.

[Josh]

Too much refrigerant in the system. You need to back the refrigerant down to 24oz with your configuration (two cans) This is from taking into account the parts list supplied above.

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.

[FABombjoy]

Low side - 32psi
High side - 150psi


Too much refrigerant in the system. You need to back the refrigerant down to 24oz with your configuration (two cans) This is from taking into account the parts list supplied above.

Those readings seem low for 80F, though. Assuming system was fully vacuumed, could charge measurement be inaccurate?

[Josh]

Those readings seem low for 80F, though. Assuming system was fully vacuumed, could charge measurement be inaccurate?

That's what i was thinking, but i will try anything at this point! So all recommendations are welcome.

System was under vacuum for about 2hrs, it should be good. Another issue may be that i replaced the compressor only, not the orifice tube and dryer. I figured since I was removing a good working compressor it was fine to retain the current parts.

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

[Bitsyncmaster]

Those readings seem low for 80F, though. Assuming system was fully vacuumed, could charge measurement be inaccurate?

+1

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

[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?? :headscratch:


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[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?? :headscratch:


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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.