Low High Side Pressure, custom AC system

[bdisab]

Hello all, I need help diagnosing what I have going on with the AC system on my car. First off I had the system evac'd and it stayed that way for a solid month, I installed a system called an Interchiller which Tee's off the Low and High pressure lines and runs to a 2nd evaporator through a 2nd dryer and it is used to super chill the coolant that is used in the factory water to air intercooler system.

The recharge procedure for that system is different than the normal procedure, I unfortunately misread their estimated charge amount and overcharged the system quite a bit 2x trying to dial it in, I read their specs as base charge (for the original oem a/c system) as 1.7lbs and an additional 500-550g (1-1.2lb) would need to be added on top for the expanded system (2.5-2.75lb), which was wrong the base charge is only around 1.1lb and total around 1.7lbs I did this 2x and couldnt get the system to work for obvious reasons, Im assuming I have damaged the compressor but I am looking for opinions before I replace it.

I have a pretty close charge in the car now but a few things are happening. First when the car is off for a while and I check the pressures the low side is around 100-105 but the high side is at around 40-50, its my understanding they should be equal or very close to equal. I have access to the AC Evap temp data and that temp only drops close to target if the car is moving and the RPM's are up, as soon as the car is back at idle the temp just climbs way back up. I have both cooling fans commanded to 100% in the car's tune when the car isnt moving, so its not from a lack of airflow across the condenser when the car isnt moving.

What I am seeing is a consistently low high side pressure reading, from when the car is off to when its running, would that point to the compressor or blockage or both or something else?

Also, the compressor spec's SP-20 oil, according to Sanden's site PAG-100 is comparable to SP-20, but every parts store and search I do says PAG-46 is the proper alternative, any insight on what the proper oil I should be using other than SP-20?

I appreciate any input you guys can give,
Thanks
Ben

[JohnHere]

I've been thinking about your post since you wrote it on Saturday, and I have several questions to help clear-up some things.

Hello all, I need help diagnosing what I have going on with the AC system on my car.

What is the model year, make, model, and engine type/size of your car, and is this a USA-spec vehicle?

First off I had the system evac'd and it stayed that way for a solid month, I installed a system called an Interchiller which Tee's off the Low and High pressure lines and runs to a 2nd evaporator through a 2nd dryer and it is used to super chill the coolant that is used in the factory water to air intercooler system.

What is an Interchiller and what does it do? Is this some kind of device to cool the air/fuel mixture before the mixture reaches the combustion chambers? Never heard of this equipment on any USA-market factory vehicle.

I have a pretty close charge in the car now but a few things are happening. First when the car is off for a while and I check the pressures the low side is around 100-105 but the high side is at around 40-50, its my understanding they should be equal or very close to equal. I have access to the AC Evap temp data and that temp only drops close to target if the car is moving and the RPM's are up, as soon as the car is back at idle the temp just climbs way back up. I have both cooling fans commanded to 100% in the car's tune when the car isnt moving, so its not from a lack of airflow across the condenser when the car isnt moving.

What are the pressures when the engine is running at about 1,800 RPM and the compressor is engaged?

Also, the compressor spec's SP-20 oil, according to Sanden's site PAG-100 is comparable to SP-20, but every parts store and search I do says PAG-46 is the proper alternative, any insight on what the proper oil I should be using other than SP-20?

IIRC, SP-20 is a PAG oil intended for MVAC systems that have fixed-displacement compressors and use R-134a refrigerant. It's equivalent to PAG-46 in viscosity, although PAG-100 would also probably work. However, I don't recall whether SP-20 is single-end-capped or double-end-capped PAG oil.

[bdisab]

I've been thinking about your post since you wrote it on Saturday, and I have several questions to help clear-up some things.

Hello all, I need help diagnosing what I have going on with the AC system on my car.

What is the model year, make, model, and engine type/size of your car, and is this a USA-spec vehicle?

It is a 2017 Infiniti Q60 3.0 Twin Turbo, US spec car

First off I had the system evac'd and it stayed that way for a solid month, I installed a system called an Interchiller which Tee's off the Low and High pressure lines and runs to a 2nd evaporator through a 2nd dryer and it is used to super chill the coolant that is used in the factory water to air intercooler system.

What is an Interchiller and what does it do? Is this some kind of device to cool the air/fuel mixture before the mixture reaches the combustion chambers? Never heard of this equipment on any USA-market factory vehicle.

It is an aftermarket system, the car comes from the factory with a water to air intercooler system that uses a heat exchanger to cool the fluid that in turn cools down the Intercoolers. I deleted the heat exchanger and installed the Interchiller system ( Link removed ). Its basically an evaporator that has fluid running across it and the water that cools the intercoolers is pumped across the face of it and into the intercoolers vs being cooled with the ambient air in the heat exchanger, it allows the fluid to get much colder and in turn make the air going into the engine colder. It also has a valve installed on the high pressure line activated by a switch that allows me to close off the high pressure line and run only the chiller only to cool the fluid or open to run cabin air and chiller.

I have a pretty close charge in the car now but a few things are happening. First when the car is off for a while and I check the pressures the low side is around 100-105 but the high side is at around 40-50, its my understanding they should be equal or very close to equal. I have access to the AC Evap temp data and that temp only drops close to target if the car is moving and the RPM's are up, as soon as the car is back at idle the temp just climbs way back up. I have both cooling fans commanded to 100% in the car's tune when the car isnt moving, so its not from a lack of airflow across the condenser when the car isnt moving.

What are the pressures when the engine is running at about 1,800 RPM and the compressor is engaged?

I will have to check, I will have to see if I can hold the gauges while reving it up, but the high side has been consistently lower than what the pressure diagrams I see online suggest at whatever ambient temperature im reading them at

Also, the compressor spec's SP-20 oil, according to Sanden's site PAG-100 is comparable to SP-20, but every parts store and search I do says PAG-46 is the proper alternative, any insight on what the proper oil I should be using other than SP-20?

IIRC, SP-20 is a PAG oil intended for MVAC systems that have fixed-displacement compressors and use R-134a refrigerant. It's equivalent to PAG-46 in viscosity, although PAG-100 would also probably work. However, I don't recall whether SP-20 is single-end-capped or double-end-capped PAG oil.

According to Sanden's website "• SP-20 PAG is oil often used in older generation wobble
plate compressors, and is compatible with SP-10 oil.
> PAG 46 - double end-capped oil similar to SP-10 for
use in aftermarket A/C systems.
> PAG 100 - double end-capped oil similar to SP-20 for
use in aftermarket A/C systems. "

Im just confused because fourseasons and all the parts stores say PAG46 but Sanden says 100

Appreciate the reply, I will try to get a reading at 1800rpm asap

[bdisab]

https://www.youtube.com/watch?v=y30XbokS5BU this is a video I just took.

The cabin AC does work better when the temperature is cooler out like tonight it is 67deg right now and it got cool pretty quickly and will hit the target EVAP temp, above 75deg it will not really get cool at all unless I drive for a long time, and even then its not great. At idle the low pressure was around 30psi and climbs to about 40psi at 1800rpm, high pressure side stays at 100. I did verify the accuracy of the high pressure gauge by swapping the lines with the engine off the other day, it matched what the low pressure side was just reading so the gauge can be ruled out.

Also I am hearing some "chattering" at times coming from the A/C compressor, it stops as soon as I turn the compressor off so I am pretty sure thats where it is coming from. I didnt have a scale at the time I last charged it, I used 12oz cans and put 2 in there and a little bit from the 3rd, spec calls for 27oz but that is used loosely according to the interchiller guys, they say to use the sight glass on the drier included in their system, I have never used that method but it is free of bubbles I just see smooth liquid flow in there.

The compressor is a Sanden PXC14 model 1700 if that helps any.

[JohnHere]

What I am seeing is a consistently low high side pressure reading, from when the car is off to when its running, would that point to the compressor or blockage or both or something else?

The cabin AC does work better when the temperature is cooler out like tonight it is 67deg right now and it got cool pretty quickly and will hit the target EVAP temp, above 75deg it will not really get cool at all unless I drive for a long time, and even then its not great. At idle the low pressure was around 30psi and climbs to about 40psi at 1800rpm, high pressure side stays at 100. I did verify the accuracy of the high pressure gauge by swapping the lines with the engine off the other day, it matched what the low pressure side was just reading so the gauge can be ruled out.
Also I am hearing some "chattering" at times coming from the A/C compressor, it stops as soon as I turn the compressor off so I am pretty sure thats where it is coming from. I didnt have a scale at the time I last charged it, I used 12oz cans and put 2 in there and a little bit from the 3rd, spec calls for 27oz but that is used loosely according to the interchiller guys, they say to use the sight glass on the drier included in their system, I have never used that method but it is free of bubbles I just see smooth liquid flow in there.
The compressor is a Sanden PXC14 model 1700 if that helps any.

If this is a high-mileage car with the original compressor—together with the pressure readings you got at 1,800 RPM, plus the noise you're hearing—the compressor itself (not just the control valve) probably is faulty. A "healthy" compressor would build considerably more pressure than 100 PSI on the high side at ambient temperatures of 75°F and above.

For your reference, in factory-stock configuration, the A/C specifications that I have for your car are 19.4 ounces net weight (1.2 pounds) of R-134a, and 5.1 fluid ounces of PAG-46.

[bdisab]

What I am seeing is a consistently low high side pressure reading, from when the car is off to when its running, would that point to the compressor or blockage or both or something else?

The cabin AC does work better when the temperature is cooler out like tonight it is 67deg right now and it got cool pretty quickly and will hit the target EVAP temp, above 75deg it will not really get cool at all unless I drive for a long time, and even then its not great. At idle the low pressure was around 30psi and climbs to about 40psi at 1800rpm, high pressure side stays at 100. I did verify the accuracy of the high pressure gauge by swapping the lines with the engine off the other day, it matched what the low pressure side was just reading so the gauge can be ruled out.
Also I am hearing some "chattering" at times coming from the A/C compressor, it stops as soon as I turn the compressor off so I am pretty sure thats where it is coming from. I didnt have a scale at the time I last charged it, I used 12oz cans and put 2 in there and a little bit from the 3rd, spec calls for 27oz but that is used loosely according to the interchiller guys, they say to use the sight glass on the drier included in their system, I have never used that method but it is free of bubbles I just see smooth liquid flow in there.
The compressor is a Sanden PXC14 model 1700 if that helps any.

If this is a high-mileage car with the original compressor—together with the pressure readings you got at 1,800 RPM, plus the noise you're hearing—the compressor itself (not just the control valve) probably is faulty. A "healthy" compressor would build considerably more pressure than 100 PSI on the high side at ambient temperatures of 75°F and above.

For your reference, in factory-stock configuration, the A/C specifications that I have for your car are 19.4 ounces net weight (1.2 pounds) of R-134a, and 5.1 fluid ounces of PAG-46.

Appreciate the info, the car only has 65,000mi on it, I was just thinking maybe the compressor got hurt from heavily overcharging it a few times, it worked fine prior to the Interchiller installation. I was doing some research last night and it seems that from what I was reading the low pressure side should decrease with RPM, is this accurate?

[tbirdtbird]

Decrease somewhat but nonetheless stay between 30-35

[JohnHere]

... the car only has 65,000mi on it, I was just thinking maybe the compressor got hurt from heavily overcharging it a few times, it worked fine prior to the Interchiller installation.

It's possible that the control valve or a reed valve sustained damage from the overcharge.

I was doing some research last night and it seems that from what I was reading the low pressure side should decrease with RPM, is this accurate?

As tbirdtbird alluded, an electronically controlled variable-displacement compressor like your car has should maintain a relatively stable low-side pressure regardless of engine RPM.