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AC blowing hot

anumeric on Tue October 09, 2007 10:20 PM User is offline

Year: 1989
Make: Nissan
Model: 240sx
Engine Size: 2.4L
Refrigerant Type: r134
Ambient Temp: 90
Pressure Low: -30
Pressure High: 150
Country of Origin: United States

Hello I purchased a Nissan 240sx earlier this year and the ac wasn't working due to a leak and belt supposedly. Well today I decided to retrofit it and get it working. So I purchased a new receiver/drier and retrofit kit. The system calls for 7 oz. of oil so I removed the ac compressor and drained out the old mineral oil and fill it with ester oil 3.5 oz. and put 3 oz. into the receiver/drier. I evacuated the system for about 25 minutes and the it held vacuum for 10 minutes with no loss. The system called for 32-35 oz. of r-12 so I charged it with 24.6 oz. of r-134 which is about 80% of the r-12 specs which I had always been told to do. The air blows hot out of the vents at about 100 degrees according to my thermometer. The ac clutch is engaging and the belt is new. The controls work in all modes and the air gets hotter when I slide the temperature controls to hot, so I assuming the temperature blend door is working properly. And I was getting a -30 on my low side and 150 on my high side with it being about 90 degrees outside. Did I overfill my receiver/drier and caused a restriction in the flow? Or is there something else I should be looking into?

I didn't have a chance to diagnose it anymore today due to work and school. Any help to point me in the right direction would be much appreciated.

Thanks in advance,
Wei



Edited: Tue October 09, 2007 at 10:27 PM by anumeric

iceman2555 on Tue October 09, 2007 10:59 PM User is offlineView users profile

With a -30 on the low side..there is something wrong for sure. It is possible that the rec/drier is over filled with lubricant....but my first thoughts are for the TXV....seems it may be stuck in the 'closed' position. To draw the low side into a vac indicates that the restriction is near the low pressure service port.
A test for rec/drier restriction is that the inlet will be warm to hot and the outlet will be a bit cooler.
Did you locate the source of the leak? Simply because it held a vac for this time period does not mean the system is not leaking. A leak test would be a good idea...esp when the pressures equalize.
Suggestion would be to recover the refrigerant.....remove the evap (could be the leak source...look for oily spots on the evap core or in the evap case), change the TXV.
If the evap does not indicate any leakage...flush the evap to remove the residual mineral lubes.....3 oz is a bit much for the rec/drier on this vehicle....why not remove it...drain some of the lube...say 2 oz.....and replace this amount into the evap. Reinstall the drier.....unless you wish to purchase another one.....don't return it as a 'defect'...it is not defective. Install the new TXV...evac and recharge the system and retest.
Good luck!!!

-------------------------
The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

mk378 on Tue October 09, 2007 11:22 PM User is offline

I'd agree the TXV is likely the culprit. When you see a clogged TXV on a newly acquired used car you have to consider that someone may have added sealant.

2POINTautO on Wed October 10, 2007 1:32 AM User is offlineView users profile

Another vote for the TXV, R12 oils will be very noticable so do a complete inspection of the entire AC system and look for black or dark brown (almost black) dirty spots, this will be a leak, look at all fittings and around the condensor and of course the evap, any leak there that does not appear to come from the TXV seals will require a new evap core. Try to look behind the compressor clutch as good as possible too. Pay attention how the thermo bulb, capillary tube or what ever kind of thermistor is in the evap case too. I can tell you have done your homework already, good for you. You may need to buy some of that black tape for in the case too??????

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Give all the dirty details
and dont forget the LO & HI pressures
Year, Make & Model would be nice too

bohica2xo on Wed October 10, 2007 2:36 AM User is offline

A plugged TXV is the usual suspect. As 378 already pointed out, it may be clogged with something more than system debris...

The system on that vehicle is more complicated than some. It includes a thermistor in the evaporator face, as well as a "superheat sensor" that juggles both the pressure & temperature in the suction line leaving the evaporator. The control makes decisions based on the inputs from the R12 calibrated sensors. This vehicle is a poor choice for a conversion to 134a.

If you insist on conversion, make sure the system is flushed clean to bare metal before adding lubricant. The compressor is a rotary vane type, and they are not very forgiving if the oil is undercharged or the wrong type. Too much oil, and poor performance. Not enough, and you will be buying a compressor.

The evaporator housing was an added module that fits between the blower housing & heater housing. The air door actuation & seals in the heater module can cause poor A/C performance by re-heating the air. I would suggest a complete inspection of the heater module, and adjustment of the controls. Take a close look at the heater core for signs of corrosion while you have the chance.

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.

anumeric on Thu October 11, 2007 4:40 PM User is offline

anumeric on Thu October 11, 2007 4:59 PM User is offline

Thanks for the input guys. I went ahead and picked up a new TXV and installed it. I even decided to route the and mount the sensing bulbs in the same manner as I took them out. The evaporator didn't show signs of leaks and actually looked very good. I went ahead and took a look at the heater core while I was in the area and that also appears to be in sound condition. And I physically got to see the temperature blend door move like its supposed to. So I went ahead and flushed out the evaporator and the high and low pressure lines, drained out about 2 oz. of oil from the drier/receiver and replaced it in the evaporator, reinstalled everything and went through the evacuation and vacuum hold processes once again. I recharge the system and still getting about the same readings, -30 low side and 100 high side this time around. And the temperature from the vents are hanging around 95 with an outside temp of about 85 today. I felt the evaporator and the high and low lines and they all felt about 90-100 degrees roughly. I had another compressor sitting around and decided to give that one a try and got the same results with that. I put my finger over the discharge port and turned the clutch no both compressors and I felt it compression against my finger, don't know how valid that test is but I figured I would mention it. I ran out of time due to school so I didn't get a chance to remove the condenser and check it out. But what do you guys think of it possibly being a clogged condenser? Only thing I can see right now about the condenser is that the fins are in good shape and free of obstructions. Once again any insight is much appreciated. And I'll looked into in more depth this weekend when time allows.

Thanks in advance,
Wei

Chick on Thu October 11, 2007 5:13 PM User is offlineView users profile

First, are you sure the compressor is coming on when the AC is called for? Also, did you change the drier and flush the condenser?

Opps, see that the difference of pressures DO indicate the compressor is running...So either the drier or condenser appears to be plugged.....

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Chick
Email: Chick

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

Freedoms just another word for nothing left to lose

Edited: Thu October 11, 2007 at 5:23 PM by Chick

mk378 on Sat October 13, 2007 6:33 PM User is offline

The compressor is working but you have a complete stoppage somewhere between the high and low ports (on the side of the loop that doesn't include the compressor). Did you find anything in the old TXV?

iceman2555 on Sat October 13, 2007 9:50 PM User is offlineView users profile

A simple test to locate the restriction would be to test each line....for the inlet of that particular line to the outlet...test the temperature....if there is a large temp drop between the sections...that is where the restriction is located.
However, think of one other....it could be the compressor....it could simply be worn so completely inside from lack of lubricant that the darn thing simply can not pump properly. The high side pressure could be produced by the heat of the engine cooling system and perhaps some pressure increase from the compressor itself...but simply, the compressor efficiency is so low that the system is not functioning. If not mistaken that vehicle uses a vane type compressor and it is guite possible the vanes are not sealing sufficiently to produce the necessary pressures to operate the system.


-------------------------
The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

iceman2555 on Sat October 13, 2007 9:52 PM User is offlineView users profile

Forget the temp test...just re read the post...the lines have been flushed and cleaned.....the rec/drier could the restriction.....so a test could be performed there....but....if the compressor is not building sufficient pressure.......!

-------------------------
The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

bohica2xo on Sun October 14, 2007 3:48 AM User is offline

Ice:

Since his compressor is running the suction into vacuum (he shows -30) I am going to say his compressor is ok.

I would be looking for a cold spot. Where ever the restriction is, it should be very cold.

How long does the system take to equalize after shutdown?

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.

anumeric on Wed October 24, 2007 10:10 PM User is offline

Well I finally got a chance to work on it again th other day. I went ahead and flushed out the condenser and there wasn't any obstructions in there and flow air pretty easily. And I still get the same readings -30 lowside and 100 highside with outside air temp of 90 degrees. So now everything has been flushed and there didn't appeared to be any clogs in anything, at least when I blew shop air though the components they all seem to flow air very easily. I felt for temperature differences and cold spots in lines etc. and nothing. So in review everything has been flushed, new TXV, new drier/receiver, and I tried 2 different ac compressors "not new ones". Like Ice mentioned it might be my compressors but as Bohica also mentioned its pulling -30 so I assume it working. But the only thing left is the compressor though lol. What are the chances that my new TXV was already bad when I brought it? Once agaiany opinions on the matter or help very much appreciated.

Thanks in advance,
Wei

mk378 on Wed October 24, 2007 10:54 PM User is offline

Chances are real good that your TXV is blocked since you've checked everything else for blockage. May have been a bad valve or may have gotten something in it right away. It's not the compressor.

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