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Ambient Temp Determines When AC Works (or not)?

lesandjes on Wed July 20, 2011 9:36 AM User is offline

Year: 1995
Make: Lexus
Model: ES300
Refrigerant Type: R134a
Ambient Temp: 80
Pressure Low: Varies
Pressure High: Varies
Country of Origin: United States

We are 2 weeks into trying to fix an intermittent AC issue on this 1995 Lexus ES300. I searched here but cannot find anything that directly relates to our issue so thought I would post in hopes of getting some well needed advice.

The problem is that the AC system only seems to work when ambient temp outside is below 80 or so degrees. Higher than that and no cooling occurs though AC clutch seems to be turning. When it works, it cools great and the gauge readings are perfect (40 or so Low side and around 200 on high side). When it doesn't work, we get 0 on low side and maybe 75 on high side with only warm air blowing out the vents.

Here is what we have done so far:
- Replaced AC relay as this is a known issue for the model year car
- Removed refrigerant and replaced TXV assuming this was getting stuck open perhaps
- Replaced Drier since we had the system cracked open
- Tested pressure switch on Drier and it appears within spec
- Pulled vacuum on system for 30 mins with a vacuum pump and vacuum held fine
- Recharged with 34 oz of R134

After doing above, same problem persists. However, we had to jumper the relay to get the AC clutch to engage. When we did that, the Low side went into vacuum and high side went to around 125-150 or so - and only warm air was blowing. We then let the car sit in the shade and started it a few hours later and sure enough, it ran and gave perfect pressure readings and blew ice cold air. Note we still had to jumper the relay to get the AC clutch to engage but it worked fine when running.

So - I am at a loss to understand why minor variances in ambient temp (+/- 20 degrees) would affect AC operations so much. More importantly, what does this point to in terms of issue? I had thought of a blockage but I am totally confused why this would be temperature sensitive. Could the AC clutch air gap need adjusting? Again, struggling to understand how this is temp dependent though I know the coil there could be affected somewhat by ambient temp.

Any Thoughts?

Regards,

AndrewT


Edited: Wed July 20, 2011 at 10:20 AM by lesandjes

JJM on Wed July 20, 2011 11:37 AM User is offline

As for the compressor not engaging, are there any codes? Press and hold the AUTO and F/R switches simultaneously and turn the ignition on. Indicators will flash and tone will sound. Press OFF. Codes will display, if any. Write all down.

As for the pressure readings, with the low side going to zero or vacuum, sounds like moisture in the system, and it's freezing up at the TXV. Was the vacuum condition occurring before the TXV was replaced? One way to confirm is when the fault occurs, place a hot, damp rag over the TXV or pour hot water over it. If the pressures return to normal and the cooling begins, it's excessive moisture in the system. You might not have vacuumed long enough, or the vacuum pump isn't up to the task.

Problem is, I don't know how you're going to do this test with the TXV in the evaporator case. I really like Toyota products, and they're to be commended for using a TXV instead of a cheap OT, but why the heck couldn't they put the TXV is a more serviceable location???

Joe

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


mk378 on Wed July 20, 2011 12:04 PM User is offline

I'd agree, theres a blockage somewhere. If the high side port is before the condenser it could be in the condenser though it seems strange it would be intermittently blocked. Feel the lines on the high side when compressor is running but not cooling properly, after a blockage it would get cold (the blockage is working like an expansion valve). There shouldn't be anything cold on the high side, the pressure should not drop until after the TXV.

You could see pressures like that with the evaporator fully frosted over on the air side, there would also likely be frost on the suction line under the hood.

Edited: Wed July 20, 2011 at 12:05 PM by mk378

lesandjes on Wed July 20, 2011 5:19 PM User is offline

OK - the car throws code 13 which is the Evaporator Temp Sensor Ckt. But it didn't throw that code before we dug in to replace the TXV. And we had cleared/reset codes before to make sure. So that code came only after we replaced TXV. If we reset it now, it comes back. I was thinking maybe the plug did not get connected fully but we can check that next time we are in there. I am not as worried about that code right now as the car AC is acting exactly as it did before replaced the TXV in terms of behavior and gauge readings and such. We didn't get vacuum before we replaced TXV, we got 0 PSI on the low side and maybe 75 on high side. Thats why we thought we had a bad TXV valve - stuck open. We get vacuum on low side now as we put vacuum in the system before we charged.

Still unsure why temp variations are causing these adverse readings and performance.

AndrewT

bohica2xo on Thu July 21, 2011 12:00 AM User is offline

So you have to ask yourself - where does the refrigerant go to hide when this happens? How does it get there?

The answer is a POA valve. Many 1993 ~1995 Lexus models have a POA or STV . I don't have the book in front of me, but it looks like you are fighting a bad POA.

The suction side of the compressor can go into vacuum, and the refrigerant winds up sequestered behind the POA, spread out across the receiver / evaporator /etc.


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.

lesandjes on Thu July 21, 2011 9:05 AM User is offline

Quote
Originally posted by: bohica2xo
So you have to ask yourself - where does the refrigerant go to hide when this happens? How does it get there?
The answer is a POA valve. Many 1993 ~1995 Lexus models have a POA or STV . I don't have the book in front of me, but it looks like you are fighting a bad POA.
The suction side of the compressor can go into vacuum, and the refrigerant winds up sequestered behind the POA, spread out across the receiver / evaporator /etc.
B.

Yes - I had asked this same question - where was the refrigerant going!

I see your point but surprised this model would have a POA or STV valve. I thought they were mainly on cars from the 70s-early80s. Is there a way to check for certain? Also, where would this valve typically be located?

AndrewT

bohica2xo on Thu July 21, 2011 12:29 PM User is offline

Lexus was a premium car then, and they went all the way to a POA valve. Mitchell does not even mention the valve. Pics below may not be the exact model, but the are all I have. Sorry for the delay, my mobile did not have these pics stored...





Usually buried under the ABS, within a foot or so of the firewall.

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.

Edited: Thu July 21, 2011 at 12:29 PM by bohica2xo

lesandjes on Thu July 21, 2011 2:12 PM User is offline

That is great info - thx for the reply and assistance. Much Appreciated.

We will work to find and replace this component. If its not in the Mitchell library (which I have access to) than I don't know how to test it.

One quick follow-up - would this failure explain the temp sensitive functioning (and not) of the AC system?

Thx Again!

AndrewT

mk378 on Thu July 21, 2011 3:12 PM User is offline

It's probably getting stuck. Once you find the STV (which is the bulge in the low-side line in Bohica's photos), try banging on it while it is not cooling and see if cooling resumes.

lesandjes on Thu July 21, 2011 10:02 PM User is offline

The plot thickens. Multiple calls to local Lexus dealers indicate that they have no parts for (or knowledge of) any POA or STV valves on a 1995 Lexus ES300. Seems they were used on some models up to/thru 1993 when R12 was used - but not after. Thats what the Lexus dealers say. Went out and looked around thoroughly and cannot find anything that looks like this anywhere in the system either. So I don't think they are providing bad info. Seems they would want to sell us the parts if they could. Unless these are somehow integrated into another part somewhere so not available separately???

So back to same issue. When we checked today, the car started up and showed same pressure on low side as high side (around 90). After running, low side slowly goes down to zero and then into vacuum over about a 1-2 minute timeframe. High side moves up to around 125-150. It was in the mid-90s here today in terms of outside temp (NJ).

What else should we check? Air gap on the clutch? Pull vacuum again and run it for a longer timeframe? The vacuum pump I am using is the 2.5 CFM unit from Harbor Freight (its brand new). Not professional quality but seems to work fine. Gauges show -30 vacuum on the low side when its running (and vacuum holds when pump is off).

AndrewT

bohica2xo on Fri July 22, 2011 12:48 AM User is offline

Lexus was hit & miss with that POA. 95's made before 10/94 certainly did have them. But, not every model had one either. Did not mean to send you on a wild goose chase, but I got bit by this one before...

In the absence of a sticking POA, you have something sealing up the system on the low side. Someplace between the TXV and the location of the low side service port.

If this problem comes & goes, it may be a hose liner collapsing. Only so much rubber line between the evaporator & the service port.

Please update when you find it - our data pool on these cars is small.

-------------------------
"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.

JJM on Fri July 22, 2011 12:50 AM User is offline

I could be wrong, but I think only the LS series Lexus used an EPR valve - which is really a POA - the ES is basically a Camry, and uses the Camry setup.

When I think of EPR valves, I think compressor mounted valves from 1960s and 1970s Chrysler AirTemp systems with the RV-2 compressor. Don't know why Lexus borrowed Chrysler terminolgy, though they both do control evaporator pressure in one form or another... but what the heck does this have to do with anything.

In any event, either your expansion valve is bad, or more likely the system is contaminated with moisture. You can't pull 30" Hg of vacuum, it's not scientifically possible, and since 1 Hg of vacuum is 25,000 microns you really can't tell if you're at 5,000 microns (unacceptable) or 750 from the gauge pointer. Plus, I wouldn't expect a whole lot of performance from anything Harbor Freight.

Since your vacuum pump is likely inadequate, you might want to flush the system thoroughly, dry it out with nitrogen, add new oil (old oil may have absorbed the moisture), replace the dryer (probably saturated), vacuum, and dry out with nitrogen again, and do a final vacuum. That should do the trick with a vacuum pump not up to the task.

Joe

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



lesandjes on Fri July 22, 2011 9:24 AM User is offline

Thx. I can re-do vacuum (my friend owns a garage and has a prof AC charing system) but don't have alot of confidence in that resolving anything. Would moisture in the system explain the fact that the system works perfectly at 75 degrees temp and doesn't at 90? I don't see how that would be temp sensitive - moisture would be there all the time and cause the issue all the time. Right??

The TXV was just replaced and brand new. I don't see that as being an issue unless it came from Lexus DOA. The drier was replaced (with new unit) as well at the same time (last week).

I can check the hoses. Thats a good idea.

AndrewT

Edited: Fri July 22, 2011 at 9:27 AM by lesandjes

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