A/C not cooling

Tiny
A1953
  • MEMBER
  • 2004 NISSAN XTERRA
  • 1.9L
  • 6 CYL
  • 2WD
  • MANUAL
  • 100,000 MILES
Compressor clutch is engaging when A/C switch is on, disengages when switch is off.
Radiator fan works well.
Condenser appears clean.
blower is working well and equal air out of vents, all warm.
Cleaned filters under dash.
checked fuses, okay but replaced with new anyway.
Bypassed thermostat on evaporator, no change.
Added r134 to low pressure side as it was reading low, but still no cool air.
This problem developed gradually.
First A/C was working intermittently only cold when driving fast, now doesn't cool at all.
Thanks for your help in figuring this out!
Tuesday, December 29th, 2020 AT 6:14 PM

67 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,268 POSTS
One of the first things I would do would be to put a set of A/C gauges on it and test the high and low side pressures to see what the state of charge is. Those numbers would also give you an idea if it was the charge or if it's a worn compressor by the way the pressures change. Those would be the most suspect parts as the problem occurred gradually. Or to verify that the charge isn't the problem do a full recovery and re-charge by weight. It should take between 1.3 and 1.5 pounds of 134A.
https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

From what you posted I suspect it is either low charge level or a worn compressor. Both would cause the same type of delayed loss of cooling.
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Wednesday, December 30th, 2020 AT 6:07 AM
Tiny
A1953
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Thanks so much for the prompt and helpful reply, Steve. I have been trying to get ahold of some A/C gauges. I will get back to you when I am able to recharge the system and check the pressures.
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Wednesday, December 30th, 2020 AT 8:55 AM
Tiny
STEVE W.
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You can usually get them at the places that do the loan a tool routine, which is sort of a gimmick anyway as most have you pay the full price of the tool, then refund the money when you return it, but it can be good if you don't think you will ever use a tool more than a couple times. Let us know what you find once you have a set on hand.
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Wednesday, December 30th, 2020 AT 9:03 AM
Tiny
A1953
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Thank you so much. You 2CarPros are a Godsend.
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Wednesday, December 30th, 2020 AT 10:08 AM
Tiny
A1953
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  • 40 POSTS
Thanks again! Still waiting for a chance to get to the auto parts store for the vacuum gauge loan. Would it be a good idea to replace the expansion valve while I am at it?
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Wednesday, December 30th, 2020 AT 3:00 PM
Tiny
STEVE W.
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Not yet. I wouldn't do anything until you can do some testing. No reason to spend money on parts you may not need.
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Wednesday, December 30th, 2020 AT 3:53 PM
Tiny
A1953
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Great. Thanks!
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Wednesday, December 30th, 2020 AT 4:24 PM
Tiny
A1953
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Hi Steve. I was able to get ahold of vacuum gauges. Assuming rented gauge is correct, pressure is low, low side reads 8 PSI and high side reads 2 PSI. The clutch is not energized so I cannot tell if the compressor is compressing. Can I check the compressor at this low charge momentarily before I purge the system? Can I safely bypass the low pressure switch and where is it located?
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Saturday, January 2nd, 2021 AT 11:28 AM
Tiny
A1953
  • MEMBER
  • 40 POSTS
Air temperatures here are 80' (Hawaii).
Miswrote the gauge readings. Reading 28 PSI low and 25 PSI high. I charged with a little r134 to try to get the compressor to kick in. No joy.
Thanks again for your work.
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Saturday, January 2nd, 2021 AT 12:07 PM
Tiny
STEVE W.
  • MECHANIC
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Okay, you have a very low charge. You should see a pressure like those in the chart with the compressor working. Static pressures should be slightly higher than the temperature when you are testing, So if it's say 75 degrees you should see a static pressure around 78 PSI. That would be with the compressor off. If it's 90 degrees it would be about 95 PSI.
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Saturday, January 2nd, 2021 AT 7:28 PM
Tiny
A1953
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The AC is working great! Thank you for your excellent help!
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Sunday, January 3rd, 2021 AT 4:05 PM
Tiny
STEVE W.
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It sounds like you have some leakage, now that you know the charging methods I would put some UV dye in it and then go hunting for it. You can also look for oil staining from the oil in the system. The dye makes it much easier though. Beyond that it's great to hear you have it working.
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Sunday, January 3rd, 2021 AT 5:12 PM
Tiny
A1953
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  • 40 POSTS
Possible, but the vacuum held for an hour at -28 PSI, and I got good readings when I put the r134 into the system.
Went for a drive to return the vacuum and guages, and the A/C worked well, but quit about, 1/2 hour into the drive. Stopped for groceries and it was working again. The cooling fan works, the car is not overheating, and the blower pushes plenty air, something was signalling the compressor clutch to disengage.
Any ideas?
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Sunday, January 3rd, 2021 AT 7:32 PM
Tiny
STEVE W.
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What were the pressures at when you finished? When it shuts off then starts working after setting I would look at the system pressures while running, that somewhat suggests a higher than correct charge as the system will shut off if over pressure than may start working once the pressure has equalized.
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Monday, January 4th, 2021 AT 6:40 AM
Tiny
A1953
  • MEMBER
  • 40 POSTS
225 PSI high side and around 60 low side. Holding steady for 30 minutes with vehicle idling. Pressures dropped when I occasionally turned off the A/C, but I didn't check the exact final static pressures. Weather temperature here was around 80.
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Monday, January 4th, 2021 AT 7:36 AM
Tiny
A1953
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I can borrow the guages again if need be.
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Monday, January 4th, 2021 AT 9:36 AM
Tiny
STEVE W.
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For 80 that's about 15 PSI high and could be the issue if the high pressure cut out is a bit aged. The only way to know for sure would be to run it until it shuts off and then see what the pressures are when it shuts down. Attached are the numbers the switch should operate at. The increasing numbers are where the switch cycles So on the low side the switch turns on at a pressure higher than about 25 PSI and off at about the same The high side will shut off the A/C at a pressure above about 400 PSI and as the pressure drops it turns back on between 200-250. So a weak switch could easily be turning the system off at 350 or so, and it comes back when it drops back below that. But I would check the pressures simply because running them high can easily damage the system.
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Monday, January 4th, 2021 AT 3:38 PM
Tiny
A1953
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Okay, thanks! I will get the guages again because it will be good to know. Are you thinking maybe the electrical component of the switch, or likely a sensor replacement that will require another vacuum of the system?
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Monday, January 4th, 2021 AT 5:55 PM
Tiny
STEVE W.
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I would check the pressures first, it may be that they just need to be lowered a bit to make it work properly. There is also the possibility that it was working too well and iced up the evaporator core, that would trigger the temperature sensor on the core to shut it off until it thawed out. I'm leaning more toward the pressure switch but want you to know the other items that could act that way.
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Tuesday, January 5th, 2021 AT 2:54 AM
Tiny
A1953
  • MEMBER
  • 40 POSTS
Okay. Thanks. It will be a couple of days before I can get the car long enough to check the pressures. I will let you know then. In the meantime, we will not use the A/C.
I am pretty perplexed because outwardly, the system is performing similarly to when it was definitely short on refrigerant. Intermittently, and never really getting ice cold.

Thanks again for your help.
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Tuesday, January 5th, 2021 AT 3:17 AM

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