2009 Pontiac G3 AC Probs (DIY diagnosed and repaired! With pics)

[The_Limey]

Since my wife bought the car from Hertz, the AC has never worked properly. It's just not very cold. She took it to Pepboys to have a leak test conducted and they told her (amongst a host of other things that needed replacing) there was zero pressure in the system and it required a new condenser and compressor.

Having purchased both new parts, I disassembled the front of the car and as I unhooked the pipe exiting the condenser (on the dryer side) there was a huge release of pressure and PAG oil which almost gave me a heart attack. Now I'm thinking there's no leak in the condenser as there's no sign of dye anywhere, and at just over three weeks since the test there's evidently still a lot of refrigerant in the system.

I've decided not to replace the parts, but go back to diagnostics and re-checking the basics. I've checked all the fuses and with the AC turned to 4 and the coolest setting, I can hear the compressor clutch click and kick in.

Can anybody suggest something I might be missing? I've read about jumping the pressure sensor, but surely if the compressor is kicking in this must be OK?

[PoisonIvy]

Have you charged the system yourself with a home kit? Did you put dye in it yourself to find a leak?

[The_Limey]

No, this was done by Pep Boys.

[xintersecty]

Your post are misleading. It sounds like they did not fill the system and yet you had pressure and then they filled the system. So did they really fill the system?

1) you need good air flow across the evaporator coil (the one inside and makes the car cool). Have you check the air filter for the AC?

2) When you took the system apart did you allow it to completely dump? Or did you shut it down right away?

3) Most Car ACs has two pressure switches. The High Pressure acts as a safety. The low pressure is what controls the compressor. The liquid freon goes to the expansion valve or orifice as it expands it takes heat out of the evaporator. Meanwhile the compressor is sucking and compressing the gas. If there is not enough heat to expand the liquid into gas then the low pressure cuts off the compressor until there is gas to compress.

So that means until pressure goes up, then compressor will not run.

4) Buy a AC gauge kit. Well worth it to have. You should be able to see low pressure side changing up/down to cause the compressor the cycle.

5) If you compressor is running however it's not cooling then you might have an airflow issue OR a bad low pressure switch stuck on.

[The_Limey]

I'm just as confused as you are about what Pep Boys actually did to the car. According to the quote, both high and low pressure readings were zero. They charged us for dye and refrigerant, and supposedly leak tested the whole system. I think they realised my wife wasn't technically minded, did none of this, and simply quoted for the two most expensive and labour intensive parts to replace. They also said the front struts and rear shocks needed replacing (based on mileage?!), and the power steering circuit was leaking.

I'm really of a mind to just do this myself now. I'm not sure I trust garages any more. Unfortunately, due to the shock of there being a whole load of pressure still present in the system, I allowed it to totally vent along with a load of PAG oil. If I recharge the system myself and buy some AC guages, what values are typical for the high and low pressure valves? From what you said, I'm planning to replace the dryer and cabin air filter and go from there.

[xintersecty]

I'm just as confused as you are about what Pep Boys actually did to the car. According to the quote, both high and low pressure readings were zero. They charged us for dye and refrigerant, and supposedly leak tested the whole system.

I had the dealer pull some crap like that on my ford. i took it the dealer for oil changes, they said my brake pads were shot. So I replaced myself, found out my pads were at half of service life. I took my spent pads to the same dealership and asked them stop lying to me and refund my oil change money. They did and lost my business for life.

Goto pep boys and ask for a refund as it stands now because of their lying, you have a more expensive repair.

To do AC work you will need a set gauges and a vacuum pump.

Guages
Get a set of gauges that show negative pressure, so that will run the cost a little more. These are well worth it for charging and keeping your friends happy.

Vacuum pump.
Here is a cheap O pump that requires shop air from harbor fright. Requires a lot of shop air, a lot.
Vacuum Pump - AC Vacuum Pump w/ R134A & R12 Connectors

If you can afforded get a real pump. They are useful pulling vacuum if you do any modeling.

The vacuum is essential for putting together a good system. It takes the moisture and contaminants out of system that will ruin the gas and compressor.

I say do the repair your self. You learn something and be set free!

[xintersecty]

And besides if the GD compressor was shot, they would have not been able to recharge the system. So they are really lying.

[The_Limey]

OK. Looks like I'm going to try and return the compressor and condenser. Luckily I didn't fit them or anything, just opened the packaging, so it should be OK.

My father-in-law has a fairly industrial-sized air compressor, so I should be OK to buy that pump you recommended. They also have a sale on a set of gauges:

AC Gauges - Save on this AC Manifold Gauge Set

Is there a rough how to guide on recharging AC systems? I'm pretty familiar with motorbikes, but this is the first car I've owned and have never tackled AC systems before. I assume I'm attaching the gauges to the two valves near the bulkhead, but am I recharging through these as well? How do I deal with the lost PAG oil when I opened the system? Can I just recharge it with an oil/refrigerant mix or does it need to be exactly the c. 200ml recommended by GM?

Edit: I've just discovered Scotty Kilmer's YouTube channel with a lot of AC repair videos. That's this afternoon's entertainment taken care of.

[xintersecty]

Is there a rough how to guide on recharging AC systems? I'm pretty familiar with motorbikes, but this is the first car I've owned and have never tackled AC systems before. I assume I'm attaching the gauges to the two valves near the bulkhead, but am I recharging through these as well? How do I deal with the lost PAG oil when I opened the system? Can I just recharge it with an oil/refrigerant mix or does it need to be exactly the c. 200ml recommended by GM?

It needs to be the 200ml. So I would just pressure everything out of there and start fresh. You basically put the oil in the system then take the vacuum down. It looks like those gauges show vacuum, then your good.

Those are good videos and do a bunch of reading. I bought a haynes book that explains everything. It also had numbers for everything. However that was years ago.

I love refrigeration as it's really about physics and thinking through the process. It's not easy but once you understand it, it's worth it.

Remember the process

cold gas -> compressed to hot liquid -> slightly cooler liquid after the condenser -> expansion valve -> takes heat from the evaporator -> cold gas

Rinse and repeat

[The_Limey]

I should really be much better at this than I am. I studied mechanical engineering at university, and had the refrigeration cycle drilled into me during our thermodynamics classes. It's just figuring out where everything is on this car and what measurements are considered normal. I'm gonna spend the rest of the day researching and then I think I'll have a crack at it.

Watch this space...