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2008 RL
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106 Posts
Discussion Starter · #1 ·
How to do a system check with a smart phone and OBD2 adapter, without opening the hood or using a manifold gauge. Gauges can damage these cars. Details to come later.

Luckily R134a has a consistent temperature-to-pressure profile. Also luckily, our cars measure both pressure and temperature.

It is best to check on an ambient temperature engine (has not ran in 8hr) and a hot cabin (car in the sun)

Monitor the 2 PIDs ambient temperature, and AC pressure, from your obd2 adapter. Key on, engine off. Compare to the chart below. Only as a rough baseline, +/-, to detect gross differences. Notice a correlation.




With a hot interior, then start the car and turn the AC on max, high fan, recirculate. Observe pressure increase.


Since the PXV16 is variable, it will not increase a set amount. I have just checked and serviced AC enough to know this is acceptable for my hot climate.
 

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Registered
2008 RL
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106 Posts
Discussion Starter · #2 ·
If the key on cold engine off pressure is:
Lower than the pressure-temperature chart, the system has a leak, or the sensors are inaccurate.

Higher than the chart, the system is overcharged, contaminated with air, excess oil, or sensors wrong.

Assuming the engine off pressure is ok
If the running pressure is:
the same as the key-off pressure, there is likely an electrical issue with the clutch and control system.

Higher than engine off, but still very low, the compressor/control valve is likely at fault. The system can still be low on charge. The TXV may be stuck open. Low 100psi even with fan on full speed and hot cabin.

Much higher than 275psi, TXV may be sticking closed, trash in front of radiator, cooling fan/module defective, contamination in system, or you live in an entirely too hot climate.

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At this point, you may feel limited in options. This system CANNOT be reliably partially "topped-off" from a can. The gauges and pressure range charts are designed for a 90s ford, not a Sanden PXV16 that stays at a constant 35psi. You need to know the weight of the refrigerant inside the system. That cannot be weighed without evacuating it with an EPA approved recycling or recovery machine. None of the pressure exposed components should be touched without evacuation. Only the clutch or electronics.

Leaks may be found with microphones, soapy bubbles, presence of oily grime at connections, or UV dye and blacklights.

If the system is fully empty, leaks may be repaired. Lines, condenser, evaporator, seals, compressor, valves, etc. The dryer must be replaced, additional oil added, and air vacuumed.
 

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2008 RL
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106 Posts
Discussion Starter · #4 ·
OK, that's a lot to take in. Hope there's not a Pop Quiz on this today.:eek:
To start, I hope a few people can just practice looking up those 2 live data points on a smart phone obd2 device, VCXNano, tech2 clone, etc.

I just link my phone a few times a year, and in 10 seconds, can verify my AC is still good to go. Its hot and humid 10 months of the year. AC is important. Too hot for top down.

I have done many of these GM systems. Complete. Compressor, valves, seals, evaporator, drier, switches, door flappers, blower motors, etc. They get easier each time.

My next chapter may be on air conditioning manifold gauges, and how they can damage up your GM vehicle, while giving false results.
 
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