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Got a weird and somewhat unhelpful error code today while trying to diagnose why my A/C compressor was not turning on. I have had the A/C system empty of freon for about a year. I evacuated it a while ago to do some front end work and then never got around to filling it. There was oil in the compressor, but no refrigerant in the lines and the A/C was not turned on (car would keep itself in Econ mode). Now that the temps are rising I would like my A/C back and went to fill the system with manifold gauges, but could never get the pressure on the high side to increase above the low side (maxed out at around 90 PSI with one can of R134a in the system). Therefore I know the A/C compressor is not turning on, but the question is why?
Only error code I have is the one pictured below, and I can't figure out if it is trying to tell me that the HVAC control module has had an internal mechanical failure or if it has sensed a mechanical failure somewhere else. I've run output tests for the A/C solenoid and hear it clicking just fine. The output test for Fan 1 does not go well, as it spins the fan a bit, but the fan is never able to get up to speed. I believe Fan 1 (passenger's side) is the A/C fan and controlled by the HVAC control module, while Fan 2 (driver's side) is the engine fan controlled by the ECM. Fan 2 runs and works just fine. After running an output test for Fan 1, I will get the ECM code P0480, but only if I run the test as the car won't produce the code by itself.
Bottom line is I think my fan issue, control module error code, and lack of engaging A/C compressor are all related, but it is still a mystery to me as what is causing what. To me there are three possibilities here:
1. Bad HVAC control module which is not able to turn on Fan 1 and thus refuses to engage compressor.
2. Bad Fan 1 that gets the signal to spin, but doesn't and thus prevents the A/C compressor from engaging.
3. Bad A/C compressor.
Given the difficult access of both the fans and A/C compressor on the S8, I would prefer it to be a control module issue. However everything else on the module and interface works just fine, so I am not sure, and would prefer not to throw parts at the problem if it is not broken. Any opinions or suggestions would be appreciated.
You can’t recharge the AC system with the old gauges and a can of R134. It’s a variable capacity compressor so that method will give misleading results and potentially result in you causing damage. You have to recharge from a vacuum by weight, and it’s very sensitive to that weight (620 grams +/- 20g). Get it outside of this range and it’ll malfunction. However I get the feeling you’ve had at it and pumped way too much R134 into it as the gauges weren’t telling you what you thought you needed to see. I hope you haven’t hydrolocked and ruined your AC compressor as a result of that, and that’s what’s giving you your mechanical failure code?
But before you panic, take it to a generic tire/repair shop and have them service/regas it the proper way with the kit they all have. More than likely that’ll fix it, as it does in 99% of cases.
Before filling I did pull a vacuum on the system for over a day and then I let it sit for another day and it stayed at -30" Hg. So I know there are no leaks and it was empty when I started to add 134a. I've only got about 20g (measuring with a scale as it goes in) from the second can into the system, so max that is in there right now would be about 360g. No more will go into the system as the pressure in the can is not enough to push it and the compressor is not engaging to make any more room. I'd take it to a shop, but I'm not sure they would have any different result.
The lack of Fan 1 functioning properly has me highly suspicious that this is some electrical or control module issue. I've checked all fuses and they are fine. Short of taking the radiator out to get to the fan, I am not sure how to diagnose it further. Also, it does seem odd that the control module still works in every other way (heater, heated seats, blower motors, etc.).
Don’t over think it. Take it to a shop with the appropriate equipment and have it properly recharged. You cannot possibly hope to diagnose any potential faults without this baseline condition being met/eliminated. The HVAC system is cleverer than you think and it simply will not allow itself to operate if it senses any pressures or temperatures being off from what it’s expecting to see.
Don’t over think it. Take it to a shop with the appropriate equipment and have it properly recharged. You cannot possibly hope to diagnose any potential faults without this baseline condition being met/eliminated. The HVAC system is cleverer than you think and it simply will not allow itself to operate if it senses any pressures or temperatures being off from what it’s expecting to see.
90 psi on this high side tells me the compressor is not turning. If you could measure the low side, I bet it would be 90 psi as well.
90 psi on this high side tells me the compressor is not turning. If you could measure the low side, I bet it would be 90 psi as well.
Right, and he’s only managed to get one can of gas in there, which is around half what’s required. The compressor won’t activate with that amount of gas in there. He either needs to figure out a way to manually get more gas in there to get it up to the 620g mark (ie refill via both high and low sides whilst its not running) using refill cans, or just have a shop do it.
06-08-2020, 09:44 AM
HVAC Control Module Code 003 - Mechanical Failure
