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Hi everyone,
I’m having a very hard time diagnosing an intermittent problem with the AC in my wife’s 2008 saturn vue. Most of the time it works perfectly, but once, maybe twice a week, it will cut out (blows warm) when she is driving somewhere. The strange thing is – the AC will function properly the next time she drives the car. For example – the AC will work fine on her way to work…then it doesn’t work when she goes to lunch….then it will work fine 4hrs later on the way home.
This is what I have checked so far:
-The refrigerant levels/pressures are within spec for both the high and low sides of the system.
-The AC clutch properly engages/disengages
-I’ve checked all of the fuses that are used by the AC system…all are OK.
-There is no CEL
-I changed the cabin air filter a few weeks agoPersonally, I think this is an electrical issue of some sort. Whether it be a bad connection, faulty sensor, or a failing relay.
From reading around, a couple of ideas that came up in other posts included: a failing AC compressor relay, or perhaps a failing coolant temp sensor?
I do have a PowerProbe and a multimeter…so I am equipped to do some electrical diagnosis. Any tips or suggestions would be greatly appreciated. Thanks!
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When you turn the ac on are both fans running? Next time it happens
see if 12v is being supplied to the compressor. if not work back from
there.If so check the connector or electrical problem with clutch.http://www.ericthecarguy.com/faq/solving-automotive-hvac-problems
Trying to catch the problem in the act might be difficult…but I will try to get the car home, and not turn it off, the next time it acts up.
I will check the cooling fans today.
[quote=”K24A4″ post=103406]Trying to catch the problem in the act might be difficult…but I will try to get the car home, and not turn it off, the next time it acts up.
I will check the cooling fans today.[/quote]
keep us posted on your progress. 🙂
Work and travel has kept me from being able to work on this problem – but the car has “acted up” the past two days. I tried to get my wife to bring the car directly home from work today, but she has a class at the gym.
However, I have some new info that might help us out.
1. The problem seems to happen when the car is left parked in the direct sun all day. My wife says it usually doesn’t happen if she parks in the shade.
2. If the AC is turned off, and the car is driven on the highway for a few minutes, the AC will usually work again.
This is starting to sound like it could be a problem with a thermostat or cooling fan? Hmmm.
My wife is going to take my car to work tomorrow, so I can work on hers. Hopefully, I can find something to report back!
There are SEVERAL things that can effect AC operation. Besides the system itself, you also have to consider the operation of the air ducts inside the HVAC assembly. That said, you provided an important clue. Most modern AC systems have a sunlight sensor on the dash. If yours if faulty, it may be giving false readings to the HVAC control and effecting AC operation. I would consult the service manual for your vehicle to find out how to test for this. Each manufacturer uses a different strategy for this type of thing. More info here.
http://www.ericthecarguy.com/faq/solving-automotive-hvac-problems
Good luck and keep us posted.
Well, today was a very eventful day!
My wife left the car with me today, so I started working on it early afternoon. Of course when I moved the car around back to our carport, the AC was working. I first checked to see if both cooling fans were running while the AC was on – and they were both running just fine.
Next, I decided to get my manifold gauges out and test the system pressures again. This is where things got real interesting….
Right as I removed the cap to the high-side service port, the schrader valve blew out, and the entire system discharged. Not good! I was well out of the way, and I had my safety glasses on, but it made me jump!
So, obviously there was a pressure problem in the system. Either the system was overcharged (I might have done this) or there is a blockage in the system. Back in May, I added about 12oz of R134A to the system…and the low side PSI never went above 30, and the high side was around 275 PSI with an ambient temperature around 80F and 70% humidity. I thought these were fairly decent numbers.
Long story short – I replaced the schrader valve on the high-side service port, and I’m going to put a vacuum on the system tomorrow. Now that the system is completely empty, I’m going to try to recharge the system with the manufacture’s specified charge of 1.26lbs or roughly 20 ounces.
If this does not work, I think I’m going to admit defeat, and take it to a shop….grrrrr.
FWIW that High side pressure looks high for 80 degree ambient air temperature… You may want to check out Eric’s video on cleaning a condenser…. Brought the high side pressure down considerably…
-Karl
Since the system discharged rapidly you might want to add a couple of oz. of oil before the recharge.
Update! The evacuation and recharge was successful!
I put a vacuum pump on the system for about 30 min, and then let it stand for 10min to see if I had any leaks. It held right around -30psi. I recharged the system with with just about 21oz of R134A (spec is 20.3 oz).
With the car running, I could hear the AC compressor kick on as I started to charge the system. I put in 1, 12oz can, then I took my high-side gauge off to see if the replaced schrader valve was holding, and it was.
I continued to charge the system, but strangely the vents were still blowing hot, and for some reason the cooling fans were not coming on. The engine seemed like it was getting a bit hot, so I turned the car off. After a few minutes I turned the car back on, and the cooling fans were now running, but the AC was still not cold. At this point I had charged the system with the full 21oz, so I decided to pull off my gauges and do some reading. At this point the low-side was reading -20psi and the high-side was around 125psi.
Before I went inside, I tried the AC one more time. Surprisingly, the air coming out of the vents felt a bit cool. Something was starting to work! I turned the car off and let it sit for another 10 min. I tried the AC again, and this time it was even colder! It seemed to be working properly!
Pretty happy with the result – I decided to performance test the AC system. The ambient air temp today was 90F and humidity was at 60% Out of the center vent on recirculate, I was getting a reading of 46F.
So the AC seems to be fixed for now. We will see if the intermittent failure problem starts again. My diagnosis is that the system was overcharged, and that the pressure sensor was shutting the compressor off when the internal pressures were getting too high. I think this also explains why the problem seemed to occur most when the car was left all day in the sun.
Ugh! Just when I thought I was out of the woods, the AC didn’t work today.
I was able to pull over when it happened, so I popped the hood, and sure enough, neither of the radiator fans were working. I know that both of the fans are good, so they obviously were not getting power.
I’m really starting to think that I have a failing main fan relay. The AC compressor was working, but the radiator fans were not. Would an AC system still blow somewhat cold air with no fans working, while you were driving, due to ram ventilation?
I did more diagnostic work today, and I’m more confused than ever. Today, the cooling fans operated properly.
However, I think I’m on to something.
I hooked up my gauges to the service ports and monitored the system for 10-15 minutes. The AC worked properly for the first few minutes, and the pressures on high (225psi) and low side (30psi) were good. But, as the system ran, the pressures of both the high and low side dropped….and the temperature of the air coming out of the vents increased proportionally. When the AC was blowing completely warm, the low side had a vacuum of -20 in/hg and the high side stayed around 150psi. This is where the gauges stayed.
I’m now thinking that there is an internal blockage in the system. Something is not letting the refrigerant return to the low side of the system. Thoughts?
I think I’m going to have to take the car to a repair shop. I’ve tried everything reasonable that the home mechanic can do….time to pass it along to someone with more tools and experience.
You might find this chart helpful:
http://www.sanden.com/objects/SANDEN_SYSTEM_DIAGNOSIS_CHART.pdf
Thanks Tomh. I was actually reading some similar literature before I saw your post.
From what I’ve read tonight, it’s looking like I have a problem with the expansion valve. I think it’s either freezing up, or it has a blockage.
Here are two diagnostic tests that I found in the service manual for my Honda (I’m guessing its about the same for most cars)
1. Expansion valve is not frosted, low pressure line is not cold, low-side gauge indicates vacuum = frozen or bad expansion valve.
2. Receiver dryer is cool to touch (should be warm) = clogged receiver dryer.
I’m going to check the expansion valve and receiver dryer tomorrow….but the diagnosis in #1 is pretty much spot on to what I’m experiencing.
More to come!
We can rule out charge. With the system pumping down. (being in a vacuum)
I would remove the metering device to see if any junk is in the inlet.
Also blow through the high side with the metering device out to see if the
line is clear. Either your metering device is defective or there is a screen
clogged on the high side. 🙂
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