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Guys it is 100 hundred degrees in NC with 90% Humidity. I could use some help. Here is where I am at:
New A6 compressor, all hoses, dryer, thermostatic valve.
Vacuumed the system to 29 in HG. Charged the system with 134a today. Charging from bottle so not sure how much freon goes into the system. Ambient temp was about 85 deg. High side pressure reached 180. Low side was 35 ish.
Not cool by much out of the vents. Maybe a couple degrees below ambient.
Observations:
Line from compressor to rear of poa valve frosted up cold. Line at the bottom of the evaporator is cold. Not sure if it is cold enough. Definitely not as cold as the line at the back of the poa.
I am not a refrigeration guy. Any help would be appreciated.
R134A won't cool as well as R12 at idle. Maybe if you had a big fan blowing across the condenser while you held the throttle at ~2000 RPM to simulate moving down the road.
Did you try driving the car to see if the vent temp came down to something reasonable? And did you actually measure the vent temps?
Your low side pressure is about what an R12 system would need, and R134A requires a lower pressure to cool effectively in an R12 system. Did you have the POA valve recalibrated for R134A?
How long did you leave the vacuum on the system? And did it hold vacuum for a long time after the pump was removed?
By the way, that's even hotter than Phoenix.
Originally Posted by Sampson
Guys it is 100 hundred degrees
Last edited by Fun71; August 31st, 2016 at 05:39 PM.
R134A won't cool as well as R12 at idle. Maybe if you had a big fan blowing across the condenser while you held the throttle at ~2000 RPM to simulate moving down the road.
I did hold the idle @ 2k but no fan on the condenser. I realize 134a will not cool as well but there should be a noticeable difference from ambient.
Did you try driving the car to see if the vent temp came down to something reasonable? And did you actually measure the vent temps?
[II did not measure vent temps but it was barely lower than ambient;
maybe 5 degrees. I did drive the car quite a bit and it did not cool down any at the vents.[/I]
Your low side pressure is about what an R12 system would need, and R134A requires a lower pressure to cool effectively in an R12 system. Did you have the POA valve recalibrated for R134A?
I did not have the poa recalibrated I have read mixed reviews on how effective this is
One of the things I noticed was the line from the compressor to the poa frosted up. The frost line stopped at the point on the poa that the thermostatic valve connects. Eventually the line would defrost and then refrost. Any thoughts?
Last edited by Sampson; August 31st, 2016 at 05:55 PM.
I think you can get about 25 degrees out of the AC system. Put a thermometer in the dash vent, shut the doors, run it on max.
How many pounds have you put in? Maybe it needs one more.
It's odd that it's frosting and thawing. I wonder if the compressor is cycling for some reason.
The poa recalibration ambiguity is whether it's worth it.
One of the things I noticed was the line from the compressor to the poa frosted up. The frost line stopped at the point on the poa that the thermostatic valve connects. Eventually the line would defrost and then refrost. Any thoughts?
Yes. I would recommend that you review the description of A/C operation in the CSM, or look up descriptions on line, for a better understanding.
In a standard refrigeration system, cooling takes place at the point of the phase change from liquid to gas (boiling), a process which requires and absorbs a certain amount of heat per unit of refrigerant, without a corresponding increase in temperature.
In the Frigidaire system used in our cars, the compressor compresses the gaseous refrigerant and pumps the compressed gas through the condenser, where it condenses, ie: where it turns into a liquid and releases heat in the process.
The liquid then proceeds into the receiver/dryer, and then into the liquid line to the expansion valve, located just before the evaporator.
The expansion valve sprays a certain amount of liquid refrigerant out in a mist, into the evaporator.
The pressure inside the evaporator is maintained at a constant level by the POA valve, regardless of temperature or compressor speed. This ensures that the expansion valve sprays refrigerant into a controlled environment inside the evaporator, where a given amount of refrigerant will behave predictably, and lower the evaporator temperature by the desired amount.
(If the pressure in the evaporator were too high, not enough liquid refrigerant would be released, and it would not expand and evaporate enough, and the temperature would be too high, while if the pressure were too low, too much liquid refrigerant would be released, and there would be too much evaporation, which would lower the temperature too much, which would cause the evaporator to ice up, which would block air flow through it, stopping the A/C from cooling the car.)
You will note that this system uses two different passive, calibrated pressure devices working in tandem:
The expansion valve and the POA valve. The expansion valve is there to vary the amount of liquid refrigerant flowing into the evaporator, so that no matter what the temperature, air flow, and refrigerant flow (compressor speed) conditions, the amount of refrigerant will always be just enough to bring the evaporator temperature down almost to freezing, but no lower.
The POA valve is there so that the expansion valve can be calibrated for a certain set of predictable conditions, which will not vary, because it was not possible to design an expansion valve to account for all of these conditions on its own.
Once the liquid refrigerant sprayed into the evaporator has evaporated (turned to gas), absorbing heat in the process, without itself getting hotter, it passes at a specifically controlled rate through the POA valve, and then through the low pressure gas line to the compressor, where it is compressed and begins its journey again.
From this description, you can see that two things are not occurring correctly in your system:
1. Cooling is occurring past the POA valve (outside of the evaporator), and
2. Cooling is excessive, as the temperature is going below freezing.
So, we can deduce that either or both of the following things is happening:
1. The expansion valve is releasing too much liquid refrigerant into the evaporator (stuck open), so that it cannot all evaporate, and is continuing to evaporate outside the evaporator, and/or
2. The POA valve is providing too much of a restriction (stuck closed), so that the liquid refrigerant released by the expansion valve is unable to evaporate inside the evaporator, and instead is seeing a sudden pressure drop just on the other side of the POA valve, where it is evaporating as it passes through the low pressure line and cooling the hose but not much else.
You could theoretically tell the difference between 1 and 2 if you looked at the evaporator as this was happening - if it was icing, then the expansion valve would be stuck open, If it was not icing, then the POA valve is probably stuck shut.
Typically, I have heard, expansion valves are more likely to fail than POA valves, so the most likely failure point is in the expansion valve, which costs about $15 at most auto parts stores, of I recall, so I'd be inclined to just buy a new one and install it.
I'd also strongly recommend recalibrating your POA valve, which you could also test, as it has to come off anyway.
Any A/C guys want to chime in and correct or clarify any of this?
No expert either but have been around it for 40 years...Well said Eric.
For a blockage, you will know if its choking based on pressure. If its icing before the evap its choked too much (or low on refrigerant and or POA output too high).Choking causes a small amount of refrigerant to flow and it instantly pulls in a bunch of heat causing the icing. If choked the high side pressure will be pretty high too. Really high pressure could be a choked expansion valve, not your case here. On the other end of that spectrum where the valve is wide open you will flood the evap coil... POA telling the expansion valve to let er rip when it shouldn't. The POA tells the expansion valve what to do based on pump speed, as mentioned. Its the throttle.
The POA (Pilot Operated Absolute) valve needs to have its pressure reduced for 134a's boiling characteristics vs R12. Well worth getting the POA recal'ed. You can drop 10* with it cal'ed properly. You should see aprox 20-25* vent delta T depending on where the RH and ambient is on a healthy system. Shade tree approach is to adjust the screw in the POA inlet CCW 1/4 turn, but why guess and have to repeatedly evac the system to play around to get it right.
Both the POA and expansion valve are cheap. If you do have to replace the expansion or POA valve be sure to replicate the play-dough munkey sheet insulation putty like the factory did.
Get the POA calibrated correctly then see what the super heat does. While its apart check the filter for trash if equipped.
[QUOTE=MDchanic
2. The POA valve is providing too much of a restriction (stuck closed), so that the liquid refrigerant released by the expansion valve is unable to evaporate inside the evaporator, and instead is seeing a sudden pressure drop just on the other side of the POA valve, where it is evaporating as it passes through the low pressure line and cooling the hose but not much else.
- Eric[/QUOTE]
I think you may be on it here Eric. See the pic of POA below. I replaced the expansion valve but not the POA. It has been a while since I put the POA back on the car but I thought I read something and bench tested it before I decided to reuse it. Maybe not. Just cannot remember. The confusing thing to me is the line going into the bottom of the evaporator is cool. The line at the top of the evaporator is warm. I blew air through the evaporator before it was reinstalled so I do not believe it could have a blockage.
Last edited by Sampson; September 1st, 2016 at 04:43 PM.
So I am leaning towards sending the POA to classic Auto Air for rebuild. Any thoughts or suggestions would be appreciated. ALso I do not have a way to reclaim the refrigerant? Should I take it to a shop to have it depressurized. In the old days we cracked the hose and let it fly.
Decisions
]Looks like Nos poa's on eBay are very pricey and I do not see any listed from the usual suppliers, which leads me to think they are unubtainium at a reasonable price.
Not sure on price or turnaround time on having mine rebuilt by Classic Auto Air. I will call to find out tomorrow. It would involve opening the system for a period of time. Will I need to replace my new dryer?
How hot are the heater hoses? Is the water control valve shutting down the flow sufficiently? Agree that the low side is a little high.
I have been wondering the same. I tried to verify the door osition today but did not see a way to do that. I can say that the heater temp control seems to be working properly.
I think your simply low on 134. The low side is a little low. The High is not high enough. Its boiling off before it hits the evap coil. With low refrigerant it will ice in that spot. It should be doing that inside the evaporator. Take it to a good AC shop before going any further for a diagnosis. Gauges are essential to trouble shooting AC.
You definitely need to take it some where to have it sucked down(recovered) if it needs to come apart. Refrigerant is highly regulated these days to prevent atmospheric discharges. You cant buy a 25lb bottle without certs, at least you cant here in the great land of Taxes.
Call the Classic or Vintage guys for advice. Both shops are friendly and willing to help you. I've dealt with the guys in Florida a bunch.
Last edited by droldsmorland; September 2nd, 2016 at 05:21 AM.
I think you may be on it here Eric. See the pic of POA below.
From what I've heard before, this is a clear sign of a stuck/broken POA. Replacement or rebuild is a good idea. If you have the equipment to do a recharge yourself (sounds like you do), then trying another expansion valve might be worthwhile, but I rather doubt it. You can also do a test setup with the hoses disconnected from the expansion valve and POA to check the low side setting and whether or not the valve is severely clogged. Just blow shop air into the expansion valve with your gauge set connected. That's also how the unit is recalibrated, it's just pretty awkward to do on the car.
It is very important to track how much refrigerant enters the system. The rule of thumb is use 80% of the R-12 charge when charging with R-134a. Charging purely by pressures is difficult. Can be done, but it's best done with a bunch of additional information to gauge how swamped the evaporator is. Your ambient temp was fairly low, but I would have expected a higher high side with a full charge. In my experience, R-134a tends to run rather higher on the high side.
As mentioned, recalibrating the POA for R-134a is a good idea, but not critical.
Originally Posted by MDchanic
The hot water valve only closes on Max. The air should be plenty cold even with it open.
- Eric
What years/configurations? Certainly '72 puts the vacuum control for the heater valve on the hot/cold lever, with the valve closed when all the way to cold.
Originally Posted by Sampson
I have been wondering the same. I tried to verify the door osition today but did not see a way to do that. I can say that the heater temp control seems to be working properly.
If it's a concern, get a cheap diagnostic hose clamp set (look like big plastic needle nose pliers) and clamp off one of the lines while testing. Also, a borescope for your smart phone is a fantastic little tool these days. They can be had on Amazon for <$30. The pictures aren't good enough to print on a poster, but they're great for diagnostics.
Originally Posted by droldsmorland
You definitely need to take it some where to have it sucked down(recovered) if it needs to come apart. Refrigerant is highly regulated these days to prevent atmospheric discharges. You cant buy a 25lb bottle without certs, at least you cant here in the great land of Taxes.
Yeah, it's illegal to vent R-134a now. I was slow to catch on to that EPA update. Interestingly, Sams will still sell you a 25lb bottle (at least as of 6 months ago). 12 pack cases of 12oz bottles are very, very cheap there, too. Something like $60 for the case, compared to $10-$15 per bottle at the parts store.
Yeah. It varies. When I said "Max," I meant either the "Max A/C" slider or button position, or the Max Cold temperature slider position, my point being that it's only active at the extreme setting.
Originally Posted by oddball
If it's a concern, get a cheap diagnostic hose clamp set (look like big plastic needle nose pliers) and clamp off one of the lines while testing.
Or just gently use a pair of Vise-Grips (just tight enough to close the hose).
Originally Posted by oddball
12 pack cases of 12oz bottles are very, very cheap there, too. Something like $60 for the case, compared to $10-$15 per bottle at the parts store.
I paid $4 a can for 6 cans of DuPont Suva on Amazon a few weeks ago.
Thanks for all the great input above. As usual you guys on CO offer great diagnostic insight. I called Classic air this morning and sent them the pic of the POA. His immediate response was it was stuck. They are sending me a rebuilt one. This will retain the origional look vs the new replacements I found online. The rebuilt one they offer is reasonable compared to the NOS stuff I saw on epay. It will take about 2 weeks to arrive. I will then take it to a shop and have them reclaim the r 134, install the new POA and recharge the system. Droldsmoland I am not completely convinced that you are not correct that the system is not charged enough.
I will post a follow up on the results in a couple weeks. Thanks again for the help.
Steve
Wish I would have seen this a few days ago. I rebuild these poa valves and could have had one out to you in a couple of days. I used to work for CAA in Tampa
Last edited by banny; September 3rd, 2016 at 05:29 PM.
The system is undercharged, temp/press change at different temp's. Its frosting at at valve shows that there's where refrigerant is picking up heat, need guy to correct charge that has knowledge. We like to think we can fix everything but....
August 31st, 2016, 05:19 PM
