Automotive Air Conditioning Information Forum (Archives)

Longitudinal on Mon August 08, 2011 4:06 PM

Year: 1998
Make: Nissan
Model: Sentra
Engine Size: 1.6L
Refrigerant Type: R134A
Ambient Temp: 90
Pressure Low: 45
Pressure High: 210
Country of Origin: Japan

I work at a Fiat shop in Columbus, OH, where I have been building a Fiat X1/9 with a Honda K20 conversion. To further add to the alphabet soup, I used a 1998 Nissan Sentra compressor.

The car is running and the AC works, but the compressor buzzes at idle speed (come off idle and buzz goes away) and the compressor gets hot, probably hotter than it should be, but I don't know apart from the fact that it will boil water off the compressor housing when the unit is operating.

Caviats:

The compressor HAD to be mounted high, above the intake manifold. It is thus the highest piece in the system and I don't know the effect that will have on lubrication.

Speaking of lubrication, I had no way of knowing how much oil to add to the system because Fiat called for a dipstick that would be inserted into the compressor to read oil level.

Ideas? Boss wants me to finish this soon because the customer is coming from Texas for the car on Friday.

TRB on Mon August 08, 2011 9:32 PM

98 Sentra called for 7 ounces of oil.

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Longitudinal on Tue August 09, 2011 9:25 AM

Quote
Originally posted by: TRB
98 Sentra called for 7 ounces of oil.

Thank you, but I am not sure what that means for me on this Fiat with mid engine and front condensor. Is the oil requirement strictly to be determined by the compressor or is the oil charge proportional to the volume of the system, thence a particular dillution of oil in the refrigerant?

mk378 on Tue August 09, 2011 9:31 AM

How much oil is in there? It should be at least the 7 oz, considering you have longer lines than the front-engine Sentra.

Oil distributes itself through the system, though of course the compressor is the only part that needs to have it. There has to be enough to keep the heat exchangers and lines coated, so it returns to the compressor, but not so much that it floods stuff and interferes with cooling performance.

Longitudinal on Tue August 09, 2011 10:13 AM

I think I know where the conversation is going after I tell you this:

I am not equipped to flush the system, so I took a guess as to the amount of oil remaining in the system and the amount that it should have and charged it. Fiat does not provide a spec for oil volume, instead offering only a factory dipstick on the compressor that I am no longer using.

So...all you have to do now is tell me that I can't possibly have a properly functioning AC system without first flushing the system.

One of my fears from the beginning is that the very high mounting of the compressor is allowing oil to pool away from it.

Edited: Tue August 09, 2011 at 10:14 AM by Longitudinal

bohica2xo on Tue August 09, 2011 11:47 AM

The oil returns to compressors in systems far worse than that one. If you have enough refrigerant, it will pull the oil back to the compressor just fine.

That particular compressor would have been very low on my list of parts to build into a custom system. That is a DKV14G, and they are lubricant sensitive.

Let me guess, the boss insisted on using it because the donor wreck sentra behind the shop had a compressor that "looked kinda new"? Same boss that scheduled a cross country delivery on an unfinished car?

.
If you are stuck using that unit, let's try to sort this out. What was the "guess" on oil? Type / weight / quantity - we need to know what is in there.

B.




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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Longitudinal on Tue August 09, 2011 12:11 PM

I picked the compressor. I needed something with at least five belt grooves and as small as possible. Next time I will probably force the Honda K20's unit to work. It's a very tight fit between the top of the compressor and the engine cover. See?



Honda unit will fit marginally worse, but nothing I can't deal with.

Added about two ounces of oil to the system. DO NOT know how much was in there. The system was apart with an unknown amount of oil hiding in the lines, condenser, etc.

bohica2xo on Tue August 09, 2011 12:23 PM

Ok, what is the condensor out of?

You are using the OEM Fiat evaporator, which had a TXV. Was the Fiat system operating when you started the swap?

Was this a new compressor, or a used compressor?

.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

TRB on Tue August 09, 2011 4:16 PM

Quote
Originally posted by: bohica2xo
Was this a new compressor, or a used compressor?

Either way it's toast now or will be shortly. That hub is smoked.



-------------------------
When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

bohica2xo on Tue August 09, 2011 9:13 PM

Refresh my memory here - Are all Honda engines still reverse rotation?

Is that not a vane type compressor? From a Nissan with standard rotation?

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Longitudinal on Wed August 10, 2011 9:51 AM

Honda K series engines are right mount, "normal" rotation.

Used compressor. All the rest of the AC system is stock Fiat. The system was open when I inherited the project from the previous fabricator who had muffed the job, so I have no idea if/how well it worked. The car HAD already been converted to 134.

So you think the compressor is cooked? Based on the fact that I get a buzz at idle? Based on the fact that I can boil water off of it once it had been running for a few minutes? If I need a compressor, I need to get moving on that STP (sooner than possible.)

bohica2xo on Wed August 10, 2011 11:43 AM

Man, what a bag of snakes. You have several hours worth of work to do.

Step one when you inherit a 134a conversion is a total flush. No way to know what may be in that condensor or evaporator. With a system that has been open, if there was any PAG oil in it you have waterlogged PAG.

I would break the system down & flush the evaporator & condensor with a strong solvent & plenty of compressed air. A fast drying solvent like brake cleaner can be used to make sure the parts are oil free in a hurry - just be careful & do this outdoors away from ignition sources.

A new or reman compressor & a new dryer should be installed. 7 ounces of 100 oil (either ester or PAG) should be added before you close things up & evacuate. If you chose to use PAG, use the DEC PAG. Either one should come from a fresh sealed container.

Get at least 12 ounces of refrigerant into the system before you start the compressor. You may see high side pressures as much as 3 times the ambient temperature on a conversion like this. That means at 90f ambient, 270 psi is not a surprise.

Once you have about 20 ounces in it, raise the engine speed to 2000 rpm, and monitor pressures as you complete the charge. Doors open, cabin fan on highest speed. Add an ounce of refrigerant at a time, then let the system equalize for a minute. At some point you will see the high side pressure "level off" - you will see little or no change in high side pressure after adding refrigerant. This means the receiver is holding the extra liquid refrigerant. If you keep adding, you will see a big spike in pressure - this means you are overcharged. Once you see the plateau in high side pressures, stop adding refrigerant. If you see a spike, recover an ounce or two.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Longitudinal on Wed August 10, 2011 2:24 PM

I didn't inherit the AC conversion, only the ENGINE conversion. It was a running car with working 134 converted AC when it arrived. It was disassembled when I inherited the project.

So must I assume that I have a bad/now bad compressor due to the buzzing and temperature of the unit?

Longitudinal on Fri August 12, 2011 11:12 AM

Got another JY compressor. Turns out I have a '95-97 compressor, not a '98, which is one year only.

Above it has been said to add the oil before the system is closed, but my dad has a machine that adds the oil to the closed system. Is there a reason to pour it into the system before evacuation has begun?

Putting this system back together today.

I hate AC.

ice-n-tropics on Fri August 12, 2011 1:44 PM

Vane rotary compressors often buzz at idle, as on Saturns.
Reason is that centrifugal force forces the 5 vanes against the outer housing. This force is borderline at idle. At a pinch above idle the knocking vane tip noise disappears. This is not a problem, but low idle cooling performance is a basic problem with tinney displacement vane compressors, especially controlled capacity versions with suction restriction.
Cordially,
hotrodac

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Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
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Edited: Fri August 12, 2011 at 2:00 PM by ice-n-tropics