confusing AC gauge readings

[rnln]

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.

[kuehl]

"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).

[rnln]

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?

[Ronnie's.930]

^^^

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.

[kuehl]

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.

[rnln]

Hi Ronnie,
One thing I remember is that when I charged, I forgot to close the lid (). 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?

Originally Posted by Ronnie's.930

^^^

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]

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.

Originally Posted by kuehl

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.

[Ronnie's.930]

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.)!

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.

[rnln]

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?

Originally Posted by Ronnie's.930

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.)!

[Ronnie's.930]

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.

[billybek]

Spambot reported

[Pazuzu]

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.

[Pazuzu]

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.

[rnln]

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

Originally Posted by Pazuzu

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.

[rnln]

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

Originally Posted by Pazuzu

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.

[Pazuzu]

Originally Posted by rnln

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.

[88911coupe]

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....

[rnln]

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.

Originally Posted by 88911coupe

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....

[88911coupe]

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.

[rnln]

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?