Cold valve and warm air

Electra225CustomLimited

Electra225CustomLimited

Member
I got a 1968 Electra Limited with AC. Last year the air was slightly cold, this year its not cold at all. Today I checked the pressure on the low side of the system, at the POA valve. Its was around 30 PSI. 30 PSI is what the service manual says is the right pressure

The air from the AC vents is not cold, BUT the POA valve on the pic below, gets really cold. The valve is locaded between the evaporator and the compressor low side so it the valve gets cold, the evaporator should get gold and cool the air.

Could it be a faulty expansion valve, a bad POA valve? or is the evaporator full of dirt so the air wont cool?

I think the system still is running on R12. Theres no signs of conversion to R134.

(And heater valve is shutted of)


POA valve.jpg
 
30 lbs is when the high side is at its maximum, probably 180-200. You are probably measuring it when it is equal on both sides.

When the car is not running and has stabilized, morning is a good time, the pressure should be just above ambient air temperature. IE if the air temperature is 66 degrees, pressure should be 67-69.
 
Bob said:
30 lbs is when the high side is at its maximum, probably 180-200. You are probably measuring it when it is equal on both sides.

When the car is not running and has stabilized, morning is a good time, the pressure should be just above ambient air temperature. IE if the air temperature is 66 degrees, pressure should be 67-69.
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Im measuring on the low side, at the valve when compressor is running. The pressure was higher with motor off. Temperature was around 65 and pressure was around 65 psi. Pressure at high side when compressor is running is hard for me to measure, my gauge is only for 100 psi
 
If I'm remembering my old York-compressor-based systems correctly, "65 psi at 65 F" does sound like it COULD be low, but unsure.

That vintage car, does it have a sight glass in the system? I checked w my neighbor, his '70 Pontiac has a sight glass right by the drier.

If the sight glass shows a steady stream of bubbles after the compressor has been running for a while, it's "probably" undercharged (ambient temperature needs to be above 70F/21C for this to apply).

If it doesn't show bubbles/foam, then it's probably something else, and reading the high-side pressure would tell you more.

If it does show continual bubbles, then maybe it's just undercharged?
 
Thanks! It has a sight glass, but its not that clear.

I think I have to remove the fan and check if evaporator gets cold. The POA valve gets very cold, frosty, after a few minutes. It could bte the valve or maybe the evaporator is full of dirt and dont cool the air.
 
Hey, weird, I was going to check the 68 Shop Manual to see if it had a troubleshooting section, but I can't open the Air Conditioning section - I just get blank PDFs. Anyone else?

I looked in the 67 manual, and there ARE troubleshooting steps starting at page 13-54, and there's a flowchart at the end of that section. Sounds like you're thinking correctly. (And I do see some info about sight glass for diagnosis also!)

If you can't find something obvious, still sounds like you'd really need to know if the high-side pressure is low or high, that could help zero in on where the trouble would be.
 
bittmann said:
Hey, weird, I was going to check the 68 Shop Manual to see if it had a troubleshooting section, but I can't open the Air Conditioning section - I just get blank PDFs. Anyone else?

I looked in the 67 manual, and there ARE troubleshooting steps starting at page 13-54, and there's a flowchart at the end of that section. Sounds like you're thinking correctly. (And I do see some info about sight glass for diagnosis also!)

If you can't find something obvious, still sounds like you'd really need to know if the high-side pressure is low or high, that could help zero in on where the trouble would be.
Click to expand...
If u checking on your phone the PDFs in the library dont load up well. Try PC, will load up fine.
 
Electra225CustomLimited said:
I got a 1968 Electra Limited with AC. Last year the air was slightly cold, this year its not cold at all. Today I checked the pressure on the low side of the system, at the POA valve. Its was around 30 PSI. 30 PSI is what the service manual says is the right pressure

The air from the AC vents is not cold, BUT the POA valve on the pic below, gets really cold. The valve is locaded between the evaporator and the compressor low side so it the valve gets cold, the evaporator should get gold and cool the air.

Could it be a faulty expansion valve, a bad POA valve? or is the evaporator full of dirt so the air wont cool?

I think the system still is running on R12. Theres no signs of conversion to R134.

(And heater valve is shutted of)


View attachment 16231
Click to expand...
AC is a sealed system. No dirt gets sucked in. Moisture gets in and affects performance and damages. You need specified oil in system for compressor. Maintenance involves: evacuate, vacuum, (MIN. 10 MINUTES)leak test, recharge. Good idea to inject AC dye and a bit of specified oil after recharge.

AC Pressures are in correlation with ambient temperature and humidity. Find the chart and compare your pressures to it. The chart is same for all and not specific to your vehicle.

Assess with static and dynamic AC pressure readings. Place one thermometer in front of condensor, another inside cabin outlet vent. >20 Temperature difference is good. <20 temp difference is no good.

Some of the AC service machines can detect if you have R12 freon or R134A refrigerant.
 
ac.jpg

I did some tests. I removed the fan and placed a thermometer in the eveporator.

I ran the compressor for a few minutes.

The temperature in the evaporator dropped from 62 to to 51 F. Its a cold day, 62 degrees outside. meanwhile frost was building up on the POA valve and the oil bleed line and expansion valve equalizer line . When the valve get cold, its looked like smoke coming from it due to the temperature difference.

Pressure on low side, at the valve. is around 30 PSI as it should.

Could it be the Expansion valve or POA valve that wont pass refrigerant? Some refrigerant maybe goes in the oil bleed line (from evaporator to POA valve)? The big line that goes from the evaporator to the POA valve is not that cold, valve is much colder.

/Gustav
 
Thermometer goes in front of condensor, I don't think 62 to 51 satisfies a 20-degree temperature drop. If it is outside 62 would be more like in low 40s out of evaporator. I'm putting these numbers up conservatively from a R134A system. The guys that have R12 have claimed to produce colder temperatures. The 30 PSI pressure would need to match the "chart" because it would not apply in triple digit temperatures >100F, same as in 62F in varying levels of relative humidity. Based on your findings, @30PSI on Low side, the Relative Humidity would be 20%, and Outside Temperature 80 degrees F. You have 62 degrees F so the LOW side is high.

The expansion valve is a common service part in any AC system, especially on your car due to age wouldn't be a loss to replace with any other repairs in AC. A symptom of the expansion valve failing is frost forming ( Take this with a grain of salt ). If you can easily find the POA valve replace them both. Either way you will need to evacuate for repairs or maintenance. Need to spend more time in discovery before you do this. Look at the evaporator and condensor veins that none are nicked or bent pipes, than the temperature change would occur at that location.
I have attached a chart from Bimmerboard here you can see what I was describing?

1725404424348.png
 
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GL03 said:
Thermometer goes in front of condensor, I don't think 62 to 51 satisfies a 20-degree temperature drop. If it is outside 62 would be more like in low 40s out of evaporator. I'm putting these numbers up conservatively from a R134A system. The guys that have R12 have claimed to produce colder temperatures. The 30 PSI pressure would need to match the "chart" because it would not apply in triple digit temperatures >100F, same as in 62F in varying levels of relative humidity. Based on your findings, @30PSI on Low side, the Relative Humidity would be 20%, and Outside Temperature 80 degrees F. You have 62 degrees F so the LOW side is high.

The expansion valve is a common service part in any AC system, especially on your car due to age wouldn't be a loss to replace with any other repairs in AC. A symptom of the expansion valve failing is frost forming ( Take this with a grain of salt ). If you can easily find the POA valve replace them both. Either way you will need to evacuate for repairs or maintenance. Need to spend more time in discovery before you do this. Look at the evaporator and condensor veins that none are nicked or bent pipes, than the temperature change would occur at that location.
I have attached a chart from Bimmerboard here you can see what I was describing?
Click to expand...
Thank you! I suspect the expansion valve but I dont want to open the system right now.

I cant see any bent lines. The system was quite good 3 years ago. That makes me wonder if the system could be low on freon Would that make the valve to freeze?
 
In my experience - tentatively, yes. If the fluid boils too early, that is where the system will cool. If it completes boiling outside of the evaporator, you will not get much cooling in the car. (I'd expect that to be more at the expansion valve than at the POL, but I do not know for certain. If the working pressure is low enough that the POL stays "closed", and ALL of the boiling happens AFTER the evaporator...could that be the symptom you see?)

If you don't have a gauge that will read the high-side pressure, that limits your ability to troubleshoot.

In the interim: Can you clean the sight glass? e.g. Alcohol or ammonia (window cleaner) on a cotton swab? That is a somewhat-clumsy, but still usable tool that is available until you do find a gauge. If you see foaming/bubbles after ~5 minutes of operation, then (assuming that ambient temperatures are warm enough) that is an indication of a problem that could include low Freon. If you do not see bubbles, that doesn't prove that the system is "good", but seeing them does show that something is "bad" - and that it is likely low on Freon.
 
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bittmann said:
In my experience - tentatively, yes. If the fluid boils too early, that is where the system will cool. If it completes boiling outside of the evaporator, you will not get much cooling in the car. (I'd expect that to be more at the expansion valve than at the POL, but I do not know for certain. If the working pressure is low enough that the POL stays "closed", and ALL of the boiling happens AFTER the evaporator...could that be the symptom you see?)

If you don't have a gauge that will read the high-side pressure, that limits your ability to troubleshoot.

In the interim: Can you clean the sight glass? e.g. Alcohol or ammonia (window cleaner) on a cotton swab? That is a somewhat-clumsy, but still usable tool that is available until you do find a gauge. If you see foaming/bubbles after ~5 minutes of operation, then (assuming that ambient temperatures are warm enough) that is an indication of a problem that could include low Freon. If you do not see bubbles, that doesn't prove that the system is "good", but seeing them does show that something is "bad" - and that it is likely low on Freon.
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Thanks!

I cleaned the sight glass and tomorrow is gonna be warm ans sunny. I also have to order a gauge set
 
@bittmann Sight glass is not clear when the compressor runs. Some big bubbles and and foggy (almost like smoke). Then compressor is turned off, the class is crystal clear. Im not sure, but I looks like im short on refrigant.
 
If ambient temperature was above 70F/21C, and the observation was after running the compressor for 5+ minutes, that would be my initial diagnosis, too.

Times are different nowadays. I do not know what a can of R12 costs today, but I'll bet it's horrid. Back when I was fighting the problems with my AMCs, I would've just added a can and seen what happens. Not sure that makes sense anymore. If that is wrong, that useless can would have paid for a gauge set!

Looking at the chart GL03 shared, I wonder if low Freon is making it so the system cannot build high enough high-side pressure to adequately switch the POA valve. I don't know, have never fought this failure mode. The systems I've worked on all used pressure to switch the compressor clutch on and off to keep evaporator temperature above freezing. So when my system started to get low (bubbles in sight glass), the evaporator would ice over after running for a long time. And after losing more refrigerant, you could hear the compressor cycle off and on...off and on. POL valves don't give as much feedback, except for MAYBE the frost you describe, so not sure if that makes sense.

But I do believe "something is wrong" if those bubbles are there and all other test criteria has been met. So, in the absence of additional testing, I agree your diagnosis is likely correct.
 
I have a never system in an 1974 Pontiac. I converted that to R134. It works as it should- I have another r12 system in an 1969 Chrysler. That system was really low on gas but not Empty. I didnt know if the compressor was ok so I added one can of Frosty Cool, a questionable R12 substitute and now chat car is cold as ice.

I also suspect that system in my Buick is low, but not that low. It cools a bit, a few degrees, and gas from the compressor is quite warm. It its not low on gas, its probably the Expansion valve. If I open the system, I have to convert to R134. Its not that warm here in northern Sweden so old systems on R134 cools Quite well on R134 without adjusting the POA valve.
 
I put some more gas in the system, and the frosty valve isn't frosty anymore. But, the system doesn't cool as much as it should. Could be the POA valve or the expansion valve. Havnt checked temperature of the evaporator. Temperature outside was 77, air from vents 60. Thats not good at al. My chrysler and ponyiac goes down to 45 or so.
 
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