Riddle me this...A/C issue - need advice!

[DriveHard]

Patient - 2007 Nissan Xterra with 4.0L, 5spd auto with ~150k miles

I have only owned this car about a year and a half, and I have put very few miles on it. I got it as a project car that needed brakes, a new transmission, and suspension work. It is my trail toy!

Last week my family and I loaded up the Xterra to head to Colorado for a week of hiking, off roading, and relaxing at altitude. From Iowa to our destination is roughly 11 hours...nearly 99+% interstate travel, most if it with the cruise set at 80 mph across Nebraska.

On the journey out, it was a cool day and we start out very early (3am). I did not have to use the AC for almost the entire trip out to CO. About 2 hours from the destination the cabin started to warm up, and I flipped on the AC. Everything worked great, and we cooled down quickly. The last 40 minutes or so was stop and go traffic, and it seemed like the AC was starting to struggle to keep up. By that time temps were in the low 90's with high humidity. I attributed it to tough conditions and slow traffic. We arrived fine and mostly in comfort.

The next several days were at high altitude with no need for AC - I am one of those nerds that prefers windows open, and only runs AC when totally necessary.

Trip home - this is where things go south...

Left around 5am, headed back home. Trip through CO up until Denver, there was no AC needed. Around Denver, the heat started to build...and I flipped on the AC. Instant relief, and all was well. During the long haul across Nebraska, the family started to notice it was getting warmer and warmer. The AC started to really struggle. I noticed the cycle time on the compressor was getting shorter and shorter, and the the time "off" was getting longer and longer. Finally we pulled into Lincoln and the AC was basically not working at all anymore. The family was getting grumpy!

We stopped and ate lunch in a nicely AC'd establishment, and I noticed across the street there was a farm store. In my past, the conditions that happened would tell me that I had a small freon leak, and if I could top off the system, it might at least get us home. After finishing lunch, we ran across the street to the farm store. I bought a pound of freon, and charges the system that takes ~1.5 lbs. Shortly after starting to charge, my wife gave me the thumbs up that the system was once again blowing cool air. I thought I had the problem solved...and we were only about 3 hours from home.

We start out from Lincoln, and we have to turn the AC down a bit...not sure it has ever been this cold before! It was great...but as the miles wore on, it began to warm again. Ok, I have a small leak, and I figured we were running out of gas again...no worries, we will get home, and I will fix it then. About 30 minutes from home the AC is totally dead again, and we are resulting to open windows and gasping for air ;-)

Next day...here is where things get odd...

We got home on a Saturday...unpacked and parked the car. Next day I go out and start it up to look for leaks. The AC blows ICE COLD for about 30 minutes as I let it idle in my driveway. I could not find a leak...or even a hint of a leak.
Yesterday I drove it about 15 minutes to and from a bike ride...AC blew ICE COLD for the trip out and back.
This morning I drove about 20 minutes to work, and the AC blew ice cold the entire time...even with 100% humidity...

So now I wonder what is going on? I am guessing I have over-charged the system, but why is it slowly failing during long trips? I have a real AC gauge set, but have not yet measured the high and low side (will do it soon). Am I freezing the evaporator side over, so it won't pass air? Is the compressor slowly giving up over long duration trips? I just have not seen this type of issue before. Any advice on where to start would be greatly appreciated!

 

[ragtoplvr]

evaporator coil ices up. Or iff you have vacuum blend doors there is a heat dependent vacuum leak. Most new stuff uses servos now so doubt that.

Continued iceing of the evep will break a weld and then No ac.

You probable have a malfunctioning presser sensor.

Rod

 

[The_Nuke]

Determining whether or not the compressor was actually engaged while the abnormal behavior was observed would have been a good idea before adding freon to an unknown amount already present.

Determine high/low side pressures and go from there. If vehicle is operated in the meantime, pay attention to how the compressor is acting when cold air turns to cool turns to warm. Is it still engaged, cycling off, or what? That will certainly help diagnosing things.

Whatever you do, don't add any more freon until you take the PSI measurements though. You may already have overcharged it to dangerous levels and be on the verge of completely hosing things up with too much refrigerant.

 

[mk378]

If it gets cold once, there is enough refrigerant. There aren't gremlins under the hood removing refrigerant and replacing it when you're not looking.

This likely is icing. You can tell this by pulling over when it is not working and looking for ice on the line under the hood.

Not cooling in traffic but OK on the highway is often because the condenser fan does not work.

If the compressor engages at first on a cold start but after warming up it does not engage at all, that is often the clutch gap or the relay.

 

[DriveHard]

I can tell you for sure that I know exactly when the compressor engages and disengages. Every car I have ever owned I can tell when it cycles on and off while I am driving it. You can feel the load on the engine change, you can feel a slight "bump" in the velocity, you can just tell. I can also say it was clear from the temperature coming from the vents...it would cycle on, the air would get very cold, the shortly cycle off and the air would slowly warm up...its not hard to tell that the cycles "on" were getting shorter, and the cycles "off" were getting longer.

 

[DriveHard]

Originally Posted by mk378
If it gets cold once, there is enough refrigerant. There aren't gremlins under the hood removing refrigerant and replacing it when you're not looking.

This likely is icing. You can tell this by pulling over when it is not working and looking for ice on the line under the hood.

Not cooling in traffic but OK on the highway is often because the condenser fan does not work.

If the compressor engages at first on a cold start but after warming up it does not engage at all, that is often the clutch gap or the relay.


You have me intrigued with the "clutch gap or relay"...any advice on how to check these? It seems as it gets hotter and hotter it begins to fail to cycle properly.

 

[WyrTwister]

First thing I would verify , is the radiator cooling fan acting up ?

Cabin air filter OK ?

A/C drive belt OK .

Antifreeze level OK . Condensate drain OK . ( These may not have anything to do with the A/C ? )

Expansion device sticking / " stopping up " ? A/C electromagnetic clutch malfunctioning ? ( Might not be easy to determine ? )

Excessive air gap on the electromagnetic clutch ?

Rapid cycling , first guess is low on refrigerant .

Were it mine , if I find nothing wrong with the above , I would vacuum it down& if it holds vacuum , I would weigh in the appropriate charge of refrigerant . And see how it goes .

 

[mk378]

These long "off" cycles can also be the clutch, or the evaporator thermostat. You can test if the clutch coil is getting power when it is supposed to be on. If coil has power but not engaged, the gap is the problem. Eventually engine vibration may get it to pull in. You can accelerate that process by hitting the clutch plate but that test is extremely dangerous with moving parts.

 

[DriveHard]

Originally Posted by WyrTwister
First thing I would verify , is the radiator cooling fan acting up ?

Cabin air filter OK ?

A/C drive belt OK .

Antifreeze level OK . Condensate drain OK . ( These may not have anything to do with the A/C ? )

Expansion device sticking / " stopping up " ? A/C electromagnetic clutch malfunctioning ? ( Might not be easy to determine ? )

Excessive air gap on the electromagnetic clutch ?

Rapid cycling , first guess is low on refrigerant .

Were it mine , if I find nothing wrong with the above , I would vacuum it down& if it holds vacuum , I would weigh in the appropriate charge of refrigerant . And see how it goes .


Fan is mechanical with electronic clutch. When I turn on the AC, I can hear the fan "kick on" as the clutch speeds it up...fan seems ok
Only one belt that runs everything...seems healthy, no cracks, and everything else works fine.
Antifreeze is full, and everything is cooling properly.
Cycles got longer in "off" and shorter for "on" as the miles went on. After the long trip, it seems to cycle normally.

 

[WyrTwister]

I am an old man & have to stop every hour or two to go to the bathroom , etc. . You may not have to do that .

On your trip , when the A/C is miss behaving , does stopping & turning off the engine for a little while change the process you have described ?

Please post the temperatures and pressures you read , when you get the hoses & gauges on it .

Forgot to ask , is the cabin air fan working OK ?

 

[WyrTwister]

Many A/C - refrigeration systems have both high and low pressure switches / sensors . Would be interesting to know if the compressor is cycling on high or low pressure ?

 

[Schmoe]

Had similar problems driving the F150 from Oklahoma to Port Aransas TX. What I do, is cut AC off and open the outside vent, no cabin recirculation. Find that the vents still blow cold air for about 10 minutes, which tells me the evaporator is freezing up. Could be from heading into more humid conditions. Once the vents start getting a little warm, turn the AC back on and works pretty good for a while.

 

[WyrTwister]

Sounds like a great idea !

I have seen residential split systems frozen up from being low on refrigerant . Set the tstat to keep the condenser from coming on & the indoor fan to continuous . Trying to melt the ice blocking the airflow through the evaporator coil .

A filter stopped up sufficiently to significantly reduce air flow through the evaporator coil will also contribute to freezing up the evaporator coil ( or REALLY dirty coil ) .

 

[DriveHard]

No cabin filter on this system, and the fan blows strong through the whole cycle...even when the AC was not working, the fan was blowing strong.

 

[dwgwater]

My 2010 Pilot was doing the exact same thing on a trip from NY to Chicago last week. When I got home, I did the usual internet research and decided the symptoms were consistent with evaporator icing from a low charge. I added 2 oz of refrigerant, weighing the can on a kitchen scale to determine how much I added. The AC was back, but was still colder at 30-40 mph than at idle, so I added one more ounce. That did the trick. I'm no expert, but based on my reading and the story I just told, if you added a pound and a half, you badly overcharged it. Overcharge causes the evaporator to ice up, as does undercharge. Per the interwebs, even healthy car AC systems can lose one-half to one ounce per year, so adding just a little bit to compensate was the ticket for me.

 

[WyrTwister]

That is why it is recommended to vacuum the system down then weigh in the factory specified amount of refrigerant .

 

[DriveHard]

Originally Posted by WyrTwister
That is why it is recommended to vacuum the system down then weigh in the factory specified amount of refrigerant .


I was going to put the gauges on it, measure everything, then do just this and measure it again. My problem is I have no long road trips planned to test this out...

 

[JMJNet]

Yes, you need to measure the pressure from both sides and go from there instead of speculating what to do.

I won't worry so much about not having long drive, you should be able to test it.

 

[Yah-Tah-Hey]

My guess is low refrigerant charge causing evaporator icing. On my 04 Camry, the range of overcharged to undercharged is less than three ounces. Try what dwgwater suggested. Regards

 

[DriveHard]

if the evaporator was icing, wouldn't the volume of air coming from the vents decrease?