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A/C Works Intermittently

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Old 07-13-2016, 08:36 AM
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I'm having an issue with my A/C 2008 LR3 V8. When I turn on the AC it would get cold for a few minutes then warm/room temperature. This would cycle on and off. I had my freon checked and all looks ok. My AC guy said I had a leak at the front that he repaired, but the problem is still happening.
I checked the fuses and they seem to be ok?

Any other ideas/tips?
 

Last edited by reggie77; 11-09-2018 at 07:42 PM.
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Old 07-13-2016, 09:06 AM
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I had the same problem and it was due (I'm fairly certain) to overfilling the system. I think I had a bad set of gauges the first time I tried to fill the system and I put way too much R-134 in. Afterwards, my system started to act like yours. I let some out, but probably not enough and it continued to do that. Recently, I let a bunch more R-134 out of the system (down to proper pressures as indicated by a new set of gauges) and it seems to be behaving properly!
 
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Old 07-13-2016, 09:14 AM
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What pressure is yours set at? I took it to an AC shop and they have it at 40PSI. Are you using a recharge kit for yours?
 
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Old 07-13-2016, 09:18 AM
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Originally Posted by reggie77 View Post
What pressure is yours set at? I took it to an AC shop and they have it at 40PSI. Are you using a recharge kit for yours?
Pressures depend on ambient temps, but at about 85 degrees F, my low side pressure is about 32psi now and my high side is about 230-250psi.
 
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Old 07-13-2016, 09:19 AM
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Oh, and I used a can of R-134a picked up at my local auto store and a set of gauges from Harbor Freight.
 
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Old 07-13-2016, 09:33 AM
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Is there a chart that shows the PSI level for Temp? How did you release the freon? Did you have to get it vacuumed out or can I release it an easier way?
 
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Old 07-13-2016, 09:47 AM
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Would the PSI be different with rear vents also?
 
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Old 07-13-2016, 10:13 AM
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Amount of R-134a in the system will be different for the rear a/c vs. no rear a/c, but pressure should not be any different (BTW, I have rear a/c). I don't know of a specification anywhere for our cars for pressure... they just specify an amount from empty (grams/ounces).

Basically, what I did last time was to vacuum the entire a/c system out and then added the amount specified in grams/ounces. However, it looked like my pressure was still very low, so I added more (stupid). Later on (perhaps after fully warming up or due to other factors) the pressure climbed to much higher than I was expected. After a long time of suffering with my a/c cycling on and off (more off than on when it got really hot outside), I finally decided to release some R-134 and see if it had an effect.

Basically, I:
1. Attached the gauges I bought at Harbor Freight
2. Let the car warm up to operating temperature and set the a/c to full cold, full blower, and recirculation
3. Opened the valves on the gauge to begin reading
4. Released some R-134a until the pressures were in line with charts floating around the internet for my particular ambient temperature

As far as how to release, it is illegal to release R-134 directly to the atmosphere... you're supposed to collect it and send it off somewhere. How is any home mechanic supposed to collect the stuff? You got me. I'll just leave it at this... if you push the center pin of any LOW PRESSURE schrader valve, it will release whatever is inside of it... also, the gauges make it very simple to release. Not saying you should do that though.

And BTW, while both readings are important, I would be more concerned about the high pressure readings. Mine were up over 350 psi at times.
 

Last edited by cmb6s; 07-13-2016 at 10:17 AM.
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Old 07-13-2016, 11:46 AM
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Thanks so much for your detailed info! I'll be heading to Harbor Freight to get the proper gauges. Mine only has Low side port gauge. What's your High Pressure reading at now?
 
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Old 07-13-2016, 12:46 PM
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This is roughly what you're looking for depending on what your ambient temp is. However, both times I have charged cars (my LR3 and Audi), when I adjust the high pressure to match what is on the chart, the low pressure is significantly lower than what is specified on there. I guess the chart is just an approximation and our system might be a bit different.

I don't know if you'll see the same results that I did, but I tried to dial it in to about 250psi on the high side. It was around 85-88 degrees ambient when I did that.

I hope you get the same results that I did and you find your system overcharged. BTW, the reason I did this is because I noticed that my temp was not just getting warmer over time, but I could tell there was a reduced load on the engine (i.e. the compressor was shutting off). I monitored it with my IID tool, and that told me for certain that the compressor kept cycling on and off, on and off. I didn't know why at first, but the only thing I knew that was "wrong" with the system was the overfill. So... before trying anything drastic like replacing the compressor, I opted to let the R-134a out.

BTW, if you're going to HF to pick up gauges, don't forget a 20% off coupon.
 

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