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Continuing pressure issues Pages: 12

Rich- on Thu June 02, 2011 11:46 PM User is offline

Year: 1992
Make: Lexus
Model: LS400
Engine Size: 4.0L
Refrigerant Type: R-134a
Ambient Temp: 80
Pressure Low: 25-28psi
Pressure High: 178-400
Country of Origin: United States

Hello, I am new here, and I hope to get some help and get this issue resolved.
Started out when I got this car the a/c was fine, until about a month after I got it. The climate control a/c light started flashing meaning it had a seized compressor. I decided to just replace everything all at once being that I have no intentions of selling the car. Alright, so after replacing EVERYTHING, pulling a vacuum and checking for leaks I weighed in the charge. I used a CPS programmable charging scale to weigh in 950grams. Pressures were stable at 25-28psi low, and 168-178 high. I ran it for a while watching the pressures and the high side started rising slowly to 400psi when the safety shut it down. It started short cycling and the low side stayed consistent, but the high side would spike to 400+ when the compressor came on.
I had my dad come over who mainly works on large refrigeration equipment and he said it was a restriction, likely at the txv. I bought another OEM one which worked for about 15minutes and the pressure started rising again.
What do you suggest my next action be? I am thinking maybe a bad drier? That is the only part I had to get from the local parts store, as it is on back order at the dealer.

Parts replaced:
Drier (not OEM)
All hoses were replaced with new OEM ones, and hard lines were flushed with Hecat
Super Cool DEC PAG45 oil
Nylog Blue o-ring lubricant

I appreciate any help I can get!

TRB on Fri June 03, 2011 12:45 AM User is offlineView users profile

Run watter over the condenser and see if those pressures come down. If they do you know you have an inadequate condenser for R134a.


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mk378 on Fri June 03, 2011 12:47 AM User is offline

Is the condenser fan working? If the fan stops the condenser will overheat and high side pressure will rise into the 400's.

Rich- on Fri June 03, 2011 11:15 AM User is offline

Alright, just tried misting water over the condenser, and the pressure didn't change at all. It still continually rises to 400, the same as before. Both condenser fans are working, they aren't very loud when they come on like I would have expected, but they are on.

Would it be a wise investment to just replace them with some aftermarket SPAL, or Flex-a-Lite fans that push 1150cfm + each?

JJM on Sat June 04, 2011 12:21 AM User is offline

At this point, I'd have to suspect the either the quality of the refrigerant or excessive oil in the system (what kind of oil did you use?). Either that, or there's a restriction in the discharge line.

A plugged receiver typically results in low pressure readings all around. Is there any frosting anywhere on the high side?

Have you tested TXV operation? If you immerse the TVX sensing bulb in ice water and then hot water, what happens to the readings?


When considering your next auto A/C purchase, please consider the site that supports you:

Rich- on Sat June 04, 2011 9:12 AM User is offline

Unfortunately I have no way of accessing the txv once it is in the car. There isn't any frost on the lines. As for oil, I went off a chart from Napa online. It says 7oz of oil is needed for a dry system. I used exactly 7oz of the SuperCool DEC PAG sold on this site.

tomw on Sat June 04, 2011 12:47 PM User is offlineView users profile

Did you place the TXV bulb on the evaporator? It has to sense the temperature in order to operate the valve and let in refrigerant. It will attempt to choke the refrigerant flow if it 'thinks' [senses] the temperature of the evaporator is at/close to freezing. If it is not getting good contact, it may be mis-reporting or failing to open causing the hi pressure and apparent poor cooling.
The placement of the bulb is important, is what I am trying to say. The 'dum dum' stuff used to insulate the TXV in some installations is important also to keep the valve on the 'straight and narrow'.
If someone else noted this previously, please excuse me.

simplificate and add lightness

Rich- on Sat June 04, 2011 12:56 PM User is offline

The bulb was replaced as part of the txv. I scraped all the old stick on insulation off and used the new sheet that came with the denso part. I even sanded down the tube a little bit with 600grit paper to remove some of the oxidation.
I was reading some more on other threads and it seems that if the receiver/dryer was plugged I wouldn't be getting these symptoms, but I could have read that wrong.

Edited: Sat June 04, 2011 at 12:58 PM by Rich-

94RX-7 on Sat June 04, 2011 1:23 PM User is offline

Did you flush the system? It sounds like trash is finding its way into the TXV.

Also of note, the early LS and SC cars had an evaporator pressure regulator as well. Can you get pressure readings on either side of that valve?

This guy was having the exact same problem you're having. Might reach out to him and see what his resolution was.

bohica2xo on Sat June 04, 2011 1:26 PM User is offline

Where is the high side service port in relationship to the other system components? Between the compressor & condensor? Or?


"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.

Rich- on Sat June 04, 2011 1:49 PM User is offline

The hi port is between the outlet of the condenser, and the drier. I forgot about the other valve up there. I will take a look at the pressure there too. As for the lines being flushed, all the hardlines were cleaned with hecat at a local shope, and the soft lines were replaced with new ones.

Edited: Sat June 04, 2011 at 1:53 PM by Rich-

Rich- on Sat June 04, 2011 2:16 PM User is offline

Alright, just went out and got some more readings.
Current Temp. is 93*
Readings before the EPR:
25-30psi Low
350-400psi High (compressor turning off)

Reading after the EPR:
25-27psi Low
350-400psi High (compressor turning off)

From the time I shut the car off and walk back around to the front, Low pressure is sitting at 50psi, and High is down to 220psi.

JJM on Sat June 04, 2011 2:46 PM User is offline

I looks like Bohica hit it right on head (as always) by asking the right question about the location of the high side service port. I was thinking it was close to compressor, in which case a bad dryer would give all around low readings.

Given the location of the service port, I wouldn't be surprised if indeed there is an issue with the dryer - especially since you indicated it's the only part that was not OEM. Typically though, a bad dryer would ice up. But I think we're getting warmer now.

Oil is clearly not the issue - assuming the compressor was dry during install (some are charged with oil).


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Edited: Sat June 04, 2011 at 2:53 PM by JJM

Rich- on Sat June 04, 2011 3:14 PM User is offline

Awesome off to the parts store now! The compressor was shipped with 1oz of pag. I have been charging with a with a new drum of genetron 134a so I think the refrigerant is fine.

Rich- on Sun June 05, 2011 6:41 PM User is offline

Alright, changed the drier still no difference = / I had my dad bring over a tank of nitrogen and it flows in one side and out the other of all the lines just fine.

Rich- on Sun June 05, 2011 7:26 PM User is offline

Hmm, so I am reading on some of the Lexus forums, and it seems the EPR on these cars cause slugging issues. The fix to that is to cut a small slit in the piston. Does that sound like a possible cause for the high side pressure to get so high?

iceman2555 on Sun June 05, 2011 10:06 PM User is offlineView users profile

What is the time span from initial clutch engagement and the time the system reaches maximum pressures? Also at what RPM are these pressures derived? Please measure the inlet and outlet temps of the condenser and post this information.
How was the lubricant added to the system? It appears there is too much of something in the system....was the compressor drained prior to installation? How did you determine the compressor was shipped with 1 oz of lubricant? There is not an issue with the is definitely pumping....mind if I ask is it new or reman'd...and the manufacturer. What is a bit confusing is the vast difference between the liquid high side pressures and the suction pressures...normally when one goes exceeding high....the other follows suit.
What type vacuum pump was used on this repair? What were the ambient temps when the evacuation procedure was accomplished? Encountered a problem very similar to this a few weeks ago on a 'tech call in'. The vehicle was a late model Ford SUV with a TXV system. Since the low side pressures are so appears that there may be a restriction at the valve....thus the low side with an excessive high side pressure....keep in mind...'ya can't pump' what ya ain' got'. Meaning that because of the restriction the high side builds as a result of the excessive refrigerant encapsulated in that section of the system....and the low side is lower because of the lack of sufficient refrigerant flow. Please supply the requested information..thanks.

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

Rich- on Sun June 05, 2011 10:58 PM User is offline

Alright, pretty sure I have all these answers now.

Time from first clutch engagement to when it shuts off on high pressure=4min 37sec

RPM pressures tested at= 2k rpm as suggested in the factory service manual

Lubricant was added 3oz. to the compressor, and the rest was filled using a Yellow Jacket oil pump when the system was in vacuum through the suction line.

There was 1oz of PAG oil according to the shipping plate that covers the inlet and outlet ports (the plate has to be removed to install the old manifold onto it.)

The compressor is a NEW OEM Denso unit. TXV is also a NEW OEM Denso part.

I used a Robinair 6cfm 2 stage vacuum pump at 82*F for 1hr.

condenser inlet is 173* in and 147* out

iceman2555 on Mon June 06, 2011 7:55 AM User is offlineView users profile

Have you conducted any pressure test with the vehicle in a non elevated RPM mode? If so, what were the results? If not mistaken, this vehicle does utilize a fan blade/fan clutch...correct?
Were the temperature drop test completed at idle speed or at an elevated engine RPM? If at idle, they are acceptable, however, if the test were done at an elevated engine RPM the drop should have been different.
Try a test of the vehicle at idle, max cool, doors open, blower on high speed, repeat this test with the doors closed also. Keep RPM at idle for both test. Post results and include the condenser temps once more for this test procedure. Due to the elevated operational pressures of 134a it appears that this pressure range maybe within reason. Remember that the posted (OE) test procedures for this vehicle were for R12 not 134a. The elevated pressures of 134a may be the reason for this condition. When testing various vehicles during the 'retro fit craze' we often saw this same condition occur. One of the main issues of pressures/temperatures with a retro fitted vehicle is that the OE pressures are meaningless. The test parameters stated by OE's in that time had no relationship to the systems operating with the new 134a refrigerant.
It may be necessary to add additional cooling for this vehicle. The preference would be for the OE design however, perhaps a new fan clutch and also the addition of an aux cooling fan mounted on the condenser.
Have you attempted a road test with the vehicle to determine if the pressures remain in this range. If possible (manifold hose length) mount your gauges on the windshield (duct tape works well) and drive the vehicle in stop and go and also at moderate vehicle speeds. Determine if the pressures are maintaining this elevated range when air flow across the condenser is increase. These vehicles are basically 'bottom' breathers. There is a small opening in the grill...but it may not produce the desired amount of air flow necessary. The issue of a gradual build up of pressures seems to indicate a lack of sufficient condenser cooling. What still concerns me is the lack of increase in low side pressures when the high side is gradually increasing. The TXV wil only reduce the inlet charge by 'X' degrees and if the high side goes up....the low side normally will begin to increase also.
Another issue is the amount of lubricant in the compressor at installation. Never trust a label. Always drain a compressor and discard what ever lubricant is removed. Add back the correct amount and type to the compressor and 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

Rich- on Mon June 06, 2011 9:28 PM User is offline

okay, took some more readings. Still has the same results but with it just idling it takes 6min 14sec to read 400psi high, and 26psi low.

The core temp drop was at 2000rpm. I also thought that was a little low, tried putting water on it, this time with a hose fully on. The pressure maybe dropped 8psi on the high side and nothing on the low.

The engine is cooled by a clutch fan. The condenser has its own 2 12" fans. They are controlled by a seperate pressure sensor, and the throttle up to high at about 200psi.

As for a road test, I am going to get some new hoses at the supply house tomorrow.

Okay, the other thing I wanted to know is, there is a bulge in the suction line that goes the full length of the front of the car. It is a muffler, and it was cleaned according to the shop I took it to. It is just a few bellows inside and really nothing to get clogged, but could that possibly cause an issue because the higher pressure r134a runs at compared to r12?

Again, thanks for all the help so far guys! I really hope I can get this resolved soon, it is too hot to not have a/c haha.

JJM on Tue June 07, 2011 12:34 AM User is offline

Now this adds a whole new dimension... you didn't mention anything about mufflers. That is something that really should not be flushed because they really cannot be flushed successfully - only "straight through" lines should be flushed. Is there a muffler on the high side as well? If so flushing it would be a no-no as well.

I really hope whatever residual junk that might have been left in the muffler now hasn't recirculated back into the rest of the system.


When considering your next auto A/C purchase, please consider the site that supports you:

Rich- on Tue June 07, 2011 10:29 AM User is offline

I completely forgot about it. It is only on the suction line. The guy at the shop said that it was fine to flush it because he had done it in the past without any issues. I am gonna take the line off and cut it out and put a straight piece in just for peace of mind.

Rich- on Fri June 10, 2011 10:59 PM User is offline

Alright guys, so my a/c works awesome for the time being. I had the muffler replaced, and I bought a new EPR. Pressures are in check, and the air is nice and cold! Thanks for all your help, again.

iceman2555 on Fri June 10, 2011 11:31 PM User is offlineView users profile

Glad you were able to complete the repair. This 'extra' information would have been quite helpful in the beginning...but it is understandable. Good job!!!

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

JJM on Sat June 11, 2011 1:40 PM User is offline

Excellent! I guess I'm showing my age by assuming that when the compressor was replaced it already had a new EPR in the compressor, as was the case with 1960s and 1970s vehicles. In the case of the Lexus, the"EPR" is more like an STV, or actually a POA. Compressor must have really come apart to kill the EPR too.

Glad you're system is cooling and enjoy that nice LS... I've seen some with over 300,000 miles and look and drive like new. It's an awesome car.


When considering your next auto A/C purchase, please consider the site that supports you:

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