I am having the problem...

on 75 degrees day, around 65 degrees in my car. Vacuumed the system was done multiple times (from 1 to 2 hours each time). Charged it on low side only. Low side fluctuate at around 20-25 PSI, while high side keep coming up passed 170 PSI. I gave it some more. High side keep coming up pass 200 PSI, while low side is staying low (20 or so).

Stopped charging, closed all valves. Low side pressure keep transferring to high side.

Stopped the engine, low side increased and high side decreased. I released some on high side, then start engine and ran the A/C again. Soon start the A/C, low side transferred to high side. Up to desired pressure, around 30/170 PSI, A/C was cold (around 40-43 degree) but not for too long. Low side kept transferring to high side, soon low side down below 30 PSI and high was above 200 PSI or so, temp inside cabin increased.

So basically, refrigerant keep transferring from low to high side. Temp in the cabin was getting cold when gauges go toward 30/170, then temp in cabin increased back up when pressure on low side passed 30-35 and high side passed 170.

Does it sound like my expansion valve stuck opened therefore it keep coming from low to high side?
If you found the problem and solution, please post. Thanks.

"Charged it on low side only"
What kind of refrigerant and exactly how many ounces or grams?

Stopped charging, closed all valves. Low side pressure keep transferring to high side.
It is normal to see a noticeable 'swing' in pressures on both low and high side immediately after charging a system. When taking gauge readings the gauge valves should be closed. It is best to let the system run for about 5 minutes or so after adjusting a charge to allow the system to adjust or normalize itself to the charge.

Stopped the engine, low side increased and high side decreased.
This is normal. A TEV never fully closes.

Gauge readings should be noted with:
1) windows up and doors closed.
2) fresh air and heater vent controls closed, always put your hand under the lower dash to check the heater vent outlets to insure the rear heater box valves are closed
3) engine deck lid down resting on hoses
4) front condenser fan should be running when ac clutch engages
5) document (write it down) low and high side pressures at idle, ambient temperature outside of the car, vent temperature with a digital thermometer,
AC thermostat set fully clockwise to max cold and evap fan speed on 1 or 2

TEV's seldom failure due to a mechanical defect. Most 'failures' are either debris in the valve or moisture in the refrigerant. ON a normally operating system the basic observation is a warm refrigerant line entering the TEV and the evaporator outlet pipe will be sweating and cold.

In a perfect world, at idle, with R12 or R134a at 75F ambient you'd want to see approximately 180 psi on the high side. A low side reading of 30 psi suggests an evaporator core temperature of approximately 32F however the vent temperature could be higher due to heat gain by the time the air leaves the evaporator core and exits the vent (hence you carefully insert a digital probe or thermometer into the evaporator core).

Hi Kuehl,

Thanks for responding. I haven't used my A/C for several years because I know one of the hoses is bad . I recently have the time to replace it and vacuum the system.

Refrigerant is R134A.

When charging, the low side PSI went up and down but never up to 30. The high side keep increasing pass 200.

After Letting the car rest for an hour or so, I started the car and A/C again, refrigerant transferred from low to high and keep going. I was afraid so I turned off A/C and engine after low side went down to below 20, and high side is up closed to 300 PSI. As for temperature inside the car, it went down to cold near 30/170 PSI, and went up again after the 30/170 area.

Isn't the PSI suppose to stop changing when low side is around 30 and high side is around 170 or so?

^^^

rnln, when you were seeing those really strange gauge readings while the engine was running, was that with the engine lid closed (could't find that info in your most recent posts here)? If the engine lid is open, or you do not have a fan pointed at it (no airflow over the rear condenser, in other words), you will see a major/startling rise in high-side pressure and the vent temp will increase.

Rnln, think of the problem this way.. "is it.......man, method or material"
Let's start with method.

One more time :

Gauge readings should be noted with:
1) windows up and doors closed.
2) fresh air and heater vent controls closed, always put your hand under the lower dash to check the heater vent outlets to insure the rear heater box valves are closed
3) engine deck lid down resting on hoses
4) front condenser fan should be running when ac clutch engages
5) document (write it down) low and high side pressures at idle, ambient temperature outside of the car, vent temperature with a digital thermometer,
AC thermostat set fully clockwise to max cold and evap fan speed on 1 or 2
AND note exactly how many ounces or grams of refrigerant actually went into the system.


If you want 100% perfect you need 100% effort.

Hi Ronnie,
One thing I remember is that when I charged, I forgot to close the lid (:D). Now, I tried to start engine and run A/C twice to see if it helps after sitting a while, with both scenarios, engine lid open and close (problem is still there)

So you are saying the problem of weird gauges reading (very high PSI on high side and very low on low side) is because I don't have fan on the rear condenser?

Hi kuel,

When I charged, I did all the below except I forgot to close the engine lid. After that, I let the car sit and tried to turn on car and A/C twice to see how it performs, with both engine lid close and open.

I will try to take note of the PSI and temp this weekends and post.

Thanks.

Rnln,

No airflow through the tail condenser (what took place when you charged the system with lid open) results in very high system pressures, so you were seeing pressures that were much higher than they should have been under normal operating conditions and for the amount of refrigerant in the system. The high pressures prompted you to stop adding refrigerant, even though there was likely not enough in the system yet, and that is probably the reason that the a/c is not working correctly now (not enough refrigerant in there).

In short, the gauge readings with no airflow through the condenser are meaningless, and the thing to do now is a complete evacuation and charge "do over" using Griff's (Kuehl) check list as your guide. And not to worry, everyone has to do a/c do-overs from time to time (even Bob K.)! :D

PS - the reason a complete do-over is best, as opposed to just connecting the gauges and adding some more refrigerant to see what happens, is because all of the connecting and disconnecting is likely to introduce air into the system, so given your situation, level of experience, etc. it would be best just to start fresh.

Oh mine, oh mine.....
Complete evacuate the system now, with some refrigerant are in there? When I start several weeks ago, my system was completely empty, after several years unused. What do I do now, release refrigerant before vacuum or just plug the pump in a vacuum?

About engine lid, so I either have to close it or leave it open but have to have a fan blowing at it. Right?

I added to my post above about why I think that it would be best to do a "do-over". That's what I would do, but if Griff suggests otherwise, follow his advice.

You can let the gas out prior to attaching the pump if you want to, or simply attach the pump and the gas leaves the system immediately anyway (both ways work). Based on your info in previous posts, I bet you do not have much refrigerant in the system right now, so there won't be much released to atmosphere.

Charging with the engine lid down works better for establishing "real world" operating conditions. Like Griff explained to me some time back, lid down and engine speed at idle simulates operating in traffic - a "worst case" scenario for 911 a/c systems. Lid open and fan blowing on condenser works, but it could actually do a better job of cooling the condenser than the engine fan at idle does, so therefor, your gauge readings would not reflect true system pressures during actual vehicle use.

Spambot reported

Now that we know that you rented a crappy Autozone vacuum pump, it's worth asking another question...

Did you replace the vacuum oil before you pulled down the system? I wouldn't trust a pump that wasn't mine, but if I had to use a rental, I'd AT LEAST swap the oil, pull a vacuum down on the system for 10 minutes, then replace the oil AGAIN ,before pulling down for several hours. You will probably notice after that series that your gauges go down to 30/30 immediately, and stay there. Clean fresh oil makes a massive difference.

Are you using cans or a 30 pound tank?

If cans, how many cans did you use?

I'd also consider tossing another can in there, running the system for a drive (15, 20 minutes), then pulling that out with the pump. you might clean some junk out of the lines by circulating a load of freon in there.

I did not replace the oil. I added more to it because it was low. I will try that.
Thanks.

I am using a tank. I can't tell how much it went in, but it went in fairly quick.

Amazon.com : Accuteck S 50 lb x 0.2 oz All-In-One Digital Shipping Postal Scale with AC Postage (W-8250-50BS) : Office Products
Less than $20 shipped, plenty accurate for this work.

My car took the first 15-20 ounces immediately, then took 10 minutes to slowly add in the last 15 ounces, maybe 15 minutes total of adding gas, closing valves, checking pressure, repeating. I agree with Ronnie, you are massively undercharged.

I also think that between the fact that you didn't flush the system, didn't change the pump oil, and didn't close the decklid, that you're pushing water and junk around with your low freon charge.

Did you replace the receiver dryer? How long did it sit exposed before you got a vacuum pulled on the system? At least it seems that you don't have any severe leaks, since you said in the other thread that it held vacuum for days.

Unfortunately i was never able to get the temps below 50s even with new Mastercool pump and new yellow jacket gauges. Griff seemed feel I was still having ambient air in the system and that would make sense. I did the vacuum and recharge three times being very careful and still never got below 50 or so in the core, vent's a few degrees higher. Then the weather cooled off and I got sick of screwing with it. I may go to a tank and also change to hoses that don't require me to disconnect anything, which will reduce my potential mistakes of allowing air in. I'd hate to think the new evaporator was somehow defective. Won't know till the weather warms up....

Buck,
I hope you don't mind I am asking several questions. You said you can't be able to get it below 50, what exactly the temp you are getting? and what is the garage, or inside the car's cabin, temperature? What is the gauges PSI reading?
Thanks.

RNLN,
In my case what would happen is the ac would drop into the upper 40's right after I turned it on, then it would creep up to the lower 50's and not get any cooler (this is with digital sensor inserted in small hole into the evap core). Ambient was lower 90's IIRC. I'd get in the car and drive around to see if that helped but it would just stay in the lower 50s. Really frustrating since i'd substantially upgraded the parts and, as far as I can tell, followed the proper procedures. When I was adding the R134 and watching the temps they would never drop below upper 40's regardless of whether it was the 1st can or 3rd.

so the temp dropped after you turn on A/C, then go back up? Did you watch the gauges (PSI) to see how they act during this period of time?

Wow! Dug this up...bad case of Dejavu, have been vacuuming the system for several days off and on. Seems to hold vacuum but as I mentioned in another thread my new yellow jacket gauges never go below 26 but their "zero" setting is a white space about 3-4 degrees in width so maybe that is the issue. My old harbor freight gauges show I'm down to 30 and it holds there for hours. Did purge process on lines and added two 12 oz cans r134...never dropped below about 70 degrees and pressure 50! And 350. With 24 oz! About ready to fire a .45 round through this system. Thank goodness my RDX will freeze my butt off. Keep in mind this is a new compressor, new hoses, and thoroughly cleaned condensers, and brand new evaporator. I give up...

Is the evaporator outlet pipe Frosty or sweating?

Buck, it seems like there must be something simple that you've overlooked (easy to do, buttofcourse) - your vent temps, and pressures are way to high (as you know). I think I recall that you have almost the same components that I do, and with ambient temps like we had today, you should be able to see vent temps in the high 20s-low 30s, with highside pressure of around 220 and lowside of around 30 (idle engine speed, windows up, fan speed and thermostat on max settings).

Are you charging with the engine lid down?

Is it possible that you have an obstruction in the system - such as a plug accidentally left in the expansion valve fittings or hose or condenser fittings (like aluminum foil or rubber plug or something)? It happens!

Agree, there's definitely something wrong...however I'll definitely check the evaporator outlet to make sure it's cold. I have not inserted the temp probe into the evaporator core but will do that tomorrow. I'm going to review everything to see if I've done something seriously wrong...which seems to be the case. The performance is so out of line with expectations something has to be seriously wrong.

Fired ac up again to check Kuehl's suggestion. This is basically a repeat of last year...if I put a temp probe into the airbox its showing about 59 degrees for the core/evaporator. When I started the car, lid almost completely closed it quickly went to 25/250 then over about 5-10 minutes goes to 50/325 at idle. The outlet of the evaporator is extremely cold to the touch but not "icey". Is there any chance this could be caused by hooking the r/d up backwards? I recall there was no marking such is "in/out" so I just hooked it up as I recall the other one being set up. I'm beginning to think its something other than a little air in the system since I was very careful with the process and I've done it several times now.

Buck, I don't know what to make of your radically changing gauge readings, but I'm sure Griff will have some good suggestions.

As far as the dryer connections - the top fitting is for the hose from the evaporator and the bottom fitting is for the hose from the nose condenser.

+1

My call is replace the expansion valve.

I have seen (I have mentioned before) 425psi on the high side on an 89 930 garage queen - at idle. Plugged X valve.

Call Charlie Griffith. Seriously, piss a wee bit of money in the right direction.

The dude is very approachable.

911/930 Expansion Valves (TEV, TXV) seldom "fail" on their own, mechanically.

Things that make a TEV to appear to fail are:

1) Debris in the system. This could be residual trash from a compressor that locked up.
Or, 'jelly refrigerant oil'. We had a car in our facility years ago we named the car from hell. The client was a gentleman however he insisted we use his old Sanden compressor; which very old. We had erratic gauge readings, inconsistent. When we explored what was in the system it appeared to look like a glob of wax reminiscent of a lava lamp from the 70's; less the strobe affect and smell in the air. The glob was wax'd mineral oil left over from the R12 system. The solution was to AC liquid flush the condensers, hoses, remove TEV from evap and flush, new drier, new compressor.

2) Moisture in the system. When water moves into the TEV it can freeze and either cause the TEV to stay partially closed (low low side pressures) or stay open (high low side pressures).

Can an old TEV or a new one fail mechanically on its own. Yes. It is possible however statistically not often. So when someone decides to swap out the questionable TEV with a new one and suddenly the issue disappears .... you have to ask:
A) Was it the TEV, or
B) Was it moisture or debris.
It comes down to dollars and sense. If you add up the time to properly evacuate, charge and test vs. the cost of tossing another TEV and drier at the system, sometimes its less costly to do that. On the other hand some of us like to know what really caused the problem for situations where we come across it again.

When we pull a vacuum on a system the first procedure is to test our equipment.
This means testing the capability of the pump to pull down. Next the integrity of the service set: service hoses not on the car, will the service set allow us to pull down a decent vacuum. If all looks good then you move on to car. 2 weeks ago we 2 issues confront us. First our old faithful vacuum pump decided to retire, so a couple hundred bucks bought a brand new pump. Next, our old faithful digital manifold tried to convince us that its high side gauge wanted to be above the rest; it read 13 psi when open to ambient. So, several hundred bucks again. All this to fix one client's car that needed to get done ASAP.

How good of a vacuum is good. Well, most digital manifold gauges today will tell you on a perfect day they are either -29.75" or maybe -30". But that is rough scale in mercury. You need a 'micron' gauge to tell where you are really at and where you put it is critical. If you attach a typical micron gauge on a new pump adjacent to its service connection you might get a reading ranging from 75 to 200 microns depending upon the day. If you move that micron sensor up to your service set it could read 200 to 300 microns. And if you put a service valve port up by the front condenser it could read 500 to 750. It all depends upon the distance from the pump source, and the attitude of your pump, ambient air temp and humidity.

So, in the case of what 88911coupe is facing, after I ran through all the Pre-Flight checks of equipment, I'd remove the TEV, toss in a new drier (because the time and costs are running up), and properly pull another vacuum and charge by pressure & temperatures as well as monitor the weight of refrigerant: and writing everything down along the way because a few Tanguery's the night before and constant phone calls and emails can really screw up your game.

OK...possibly I missed something obvious...in this pic should I have both "sensors" covered with presstite? The inlet hose gets pretty cold and the outlet is cold as well. Sort of grasping at straws to find out why the pressures seem to get overly high even with a minimal charge of R134. As Charlie says I may have air in the system but I"ve been very careful and can't figure out where it would be coming in from. Just wanted to check and see if that other connection needs to be insulated or not. Hard to see but the pigtail is covered.http://forums.pelicanparts.com/uploa...1469834767.jpg

Thanks, I had the vacuum on it for some time...maybe didn't get it all out. Thanks Griff. I was somewhat confused seeing those pressure with a "relatively" small r134 charge. I'll re do it and hopefully have better results.http://yeahonlinemarketing.com/apple/images/48.gifhttp://yeahonlinemarketing.com/apple/images/6.gif
http://yeahonlinemarketing.com/apple/images/4.gif

The only component of the TEV (expansion valve) that needs to covered with Prestite insulation (black) tape is 'pig tail' sensor that exits the top of the TEV and attaches to the top of the evaporator outlet tube, secured with the metal clip. The pig tail sensor tube contains a refrigerant gas which expands and contracts with the temperature of the evaporator outlet; the gas pushes a bellow in the TEV which pushes a pin in the TEV which throttles the refrigerant flow based upon evaporator outlet temperature.

And you will want to cover the gaps in the top of the evaporator box where the evaporator outlet tube and TEV inlet tube exits the box; to reduce outside air entering the box.

Your TEV inlet hose fitting should be WARM to HOT, while the evaporator outlet should be COLD. If your TEV inlet hose fitting is cool this means you have blockage which forms an orifice somewhere south of the TEV inlet; the liquid refrigerant is expanding or changing state from a liquid to a gas, this usually happens when there is moisture (ice) or debris in the system.

Ok thanks, was hoping I found the problem. Just to clarify, the TEV body is cold, the metal pipe into the TEV is hot. I have a temp sensor and the body of the TEV is about 49 degrees, creeps into low 50s after a few minutes.. There's a tiny hole in the evaporator box that I can insert the temp probe into and get a reading on the core which is the 60's. Vent temps only getting down to mid 70s. Considering all hoses, compressor, evaporator are new, in addition to a new/additional condenser with a fan I don't know what I've done wrong....obviously something. I don't think its air in the system since I've beeb so careful when I recharged but maybe time to let a "professional" do the vacuum and recharge.

An 88 with a stock system running R134a typically uses 39-41 oz.

You have a 3 condenser system? and with 24 oz your pressures are 40% or more higher than what they should be. That typically is a sign of air in the system because your 40% undercharged.

If you pulled the perfect vacuum and all the system components are functioning as they should be, that's a sign of air unless you can rule out something else (condenser function, contaminated refrigerant, a blockage in the system ).

OK...another desperate attempts to resolve this crappy ac. I stumbled across some AC website that says the clamp holding the sensor bulb MUST be metal and the more heat conductive the better. I was using a a plastic tie wrap which is said NOT to use. Now replaced it with a metal clamp and will vacuum again and see what happens. Just curious...what would happen if the sensor bulb is not insulated? Only for a test. Wouldn't that cause TOO much coolant to flow and possibly freeze up? I WISH that was the problem I was having!

The sensing bulb 'throttles' the refrigerant flow.
The sensing bulb is suppose to 'see' temperature of the
evaporator outlet gases. If you don't have it well insulated
with Prestite tape (or your favorite color of PlayDo or Sillyputty) it will
see the ambient air temps in the Smuggler's Box Well; hence if the
sensing bulb is seeing warm all the time it will tell the TEV to keep dumping refrigerant in the core.

About TEV's

Do you have a "bad" TEV, maybe (anything is possible), however simply based on
your noted amount of refrigerant and pressures I would not go down that road yet.