Automotive Air Conditioning Information Forum (Archives)

westcl2 on Fri May 09, 2014 1:36 PM

Year: 2007
Make: Nissan
Model: Sentra
Engine Size: 2.0
Refrigerant Type: R-134
Ambient Temp: ~80
Pressure Low: 80
Pressure High: 50
Country of Origin: United States

So i'm pretty new to doing my own maintenance so please forgive my ignorance in advance.

Stuff I know:
My car has stopped blowing cold air.
It still blows air just not actively chilled air.
I have verified that it has a full refrigerant charge, and no visible leaks.
It's the wife's commuter and she is not exactly the most observant when it comes to things like this or notifying me when they occur. So I know it worked last summer, how well? i dunno but not bad enough that she complained about it
The clutch on the compressor is not activating(no clicking noise when you turn on the ac)
The serpentine belt is freely spinning, my assumption is that the clutch is not engaged but I can't see it directly to make sure

Plan forward:
check the fuse for the ac
check voltage going into compressor via voltmeter

assuming the fuse isn't broken and there is voltage reaching the compressor, my next action would be to replace the compressor. Obviously this is probably the most expensive option for this project and I'd like to get some more experienced input if there's something else I have overlooked or could check and find a cheaper option.

Thanks in advance for any advice

wptski on Fri May 09, 2014 2:50 PM

As long as you have power to one connection and ground on the other also. You can just replace the clutch coil if it's bad but it's all about access to the compressor and room for tools.

HECAT on Fri May 09, 2014 4:12 PM

So how did you verify full charge?

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westcl2 on Fri May 09, 2014 5:10 PM

@wpt would you recommend that over replacing the entire compressor? does it take a lot of specific tools or can I probably get by w/ pretty standard stuff?

@hecat well i tried to put more in but it was already at capacity, and ended up getting sprayed a bit by the uv dye that was in it to check for leaks........so unless its managed to swap pressurized freon for pressurized air i assumed it was good....is this not necessarily true?

GM Tech on Fri May 09, 2014 9:29 PM

That death kit gage you used is only accurate IF the compressor is running-- there is no way to say it is at capacity without the pump turning- you are reading just static pressure which should be around 80 psi at 75 degf ambient. The only way to know how much is in a system is to remove the frefrigerant and weigh it.....

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

wptski on Fri May 09, 2014 10:23 PM

Quote
Originally posted by: westcl2
@wpt would you recommend that over replacing the entire compressor? does it take a lot of specific tools or can I probably get by w/ pretty standard stuff?
If the clutch plate is pressed on you'd need a special puller. The drive pulley, a standard puller can be used. If the clutch is your only problem, you wouldn't have to open the system.

westcl2 on Sat May 10, 2014 7:02 AM

Shouldn't the fact that the system has maintained static pressure at 80 psi confirm that it isn't leaking?

Edited: Sat May 10, 2014 at 7:32 AM by westcl2

mk378 on Sat May 10, 2014 8:53 AM

80 psi static is enough to satisfy the low pressure cutoff, so the compressor should engage. You can't know by static pressure if it is a full charge or not, but the first problem is that the compressor doesn't engage.

When you press the A/C button, does anything happen? If the controls are trying to engage the compressor, the computer should rev up the engine slightly in anticipation of the load from the compressor.

westcl2 on Sat May 10, 2014 10:23 AM

@mk so help me work through this i'm new so i just want to make sure my thought process is correct.

isn't the r134 subsystem ideally a closed loop, so if it has maintained 80 psi isn't it reasonable to assume that the freon has not escaped?

my thought that if it were to dip down to atmospheric pressure it would signal that the system has been punctured or a seal has broken

HECAT on Sat May 10, 2014 11:02 AM

Liquid refrigerant in a container (can, jug, system, etc.) will vaporize and achieve a stable vapor pressure in relation to the ambient temperature the container is exposed to. The container will stabilize at this pressure as long as there is liquid at any level. The presence of vapor pressure only validates liquid exists; not how much. All systems leak.

-------------------------

HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

GM Tech on Sat May 10, 2014 11:06 AM

You don't understand, refrigerants are condensibles not compressibles--it is not a tire-you can't tell charge by static pressure. You can have 10 pounds or a half pound in your system and both will read 80 psi - just that more is a liquid when fuller. That 80 psi you have in there will be that until it gets down to about 4 ounces, then it will drop like a rock

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

westcl2 on Sat May 10, 2014 11:13 AM

Ok but this seems to be a question for after the compressor is functioning. Since on the low side it's meeting acceptable pressure and the compressor isn't activating doesn't that either indicate it is not receiving power or it is broken?

westcl2 on Sat May 10, 2014 11:15 AM

And isn't the freon in the can in a gas state?

94RX-7 on Sat May 10, 2014 11:21 AM

Quote
Originally posted by: westcl2
Since on the low side it's meeting acceptable pressure and the compressor isn't activating doesn't that either indicate it is not receiving power or it is broken?

Yes.

94RX-7 on Sat May 10, 2014 11:22 AM

Quote
Originally posted by: westcl2
And isn't the freon in the can in a gas state?

Some of it is, but MOST of what's in the can is a liquid until it is nearly empty.

HECAT on Sat May 10, 2014 2:34 PM

A can is about 80% full of liquid. Shake it, you can fell it. Proper charging is done with liquid weight. Yes this got off topic, but you stated you had verified charge.

-------------------------

HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

westcl2 on Sat May 10, 2014 4:35 PM

Edited: Thu May 15, 2014 at 1:42 PM by westcl2