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I’ve read about it too, I just see people boasting vent temps in the mid 40s to 50s and my car struggles to reach those temperatures at any given day which is frustrating hence why I feel like it’s an airflow issue or clogged evaporator.
low refrigerant will cause that and if your on an AC charge from 7-10 years ago, my bet is its low. Gauges will tell you everything you need to know.
 

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Discussion Starter · #22 ·
low refrigerant will cause that and if your on an AC charge from 7-10 years ago, my bet is its low. Gauges will tell you everything you need to know.
We just filled it up with 35 oz of Freon, I’ll be looking at how it performs tomorrow when the ambient temp is high with direct sunlight. I’d be happy with 60° Vent temps and ambient temps at around 100°
 

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Static pressures resting at 70, with the compressor jumped it would stay at around 20-25 on the low side (can’t remember the high side but it was around 220). With the compressor cycling and coolant temps at around 175 it would drop it all the way to 20, kick off the compressor, rise to about 45-50 then kick back on. High side pressure would go to about 230 and back down as the compressor cycled. Took just shy of 3 cans of refrigerant (35 oz). At night temps at the vent are nice and cool at around 52-53 as the cabin cools down but during the day it really struggles at idle. It improves with air flowing through the condenser
what was the ambient temperature when you got those pressure reading

Unless it was 60-65°, the low pressure seems to be low.
the high pressure reading would indicate an ambient of about 85°+

did you replace the orfice tube?
 

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what was the ambient temperature when you got those pressure reading

Unless it was 60-65°, the low pressure seems to be low.
the high pressure reading would indicate an ambient of about 85°+

did you replace the orfice tube?

I agree. knowing the ambient conditions are critical because the pressures will vary. If the outside temp was higher, i would suspect not enough refrigerant based on those pressures. You really want to report pressures under max stress conditions. 1500+RPM, fan speed on high, doors open and report the pressures while still at 1500+ RPM

Cclaro, did you fill by weigh by using a scale, or just by estimating based on can volume?

I’ve read about it too, I just see people boasting vent temps in the mid 40s to 50s and my car struggles to reach those temperatures at any given day which is frustrating hence why I feel like it’s an airflow issue or clogged evaporator.
Does spraying the condenser with water improve performance? That would signify an airflow issue, but your high side pressure doesn't seem high enough to support this.

I agree that your vent temps should be better. My 8-year old Taurus puts out vent temps in the low 40's at idle and will drop to 40 degrees once moving. My fox will do vent temps in the 35-38 degree range while just iding, but that's with a brand new fresh R-12 system.
 

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I agree with @Ilusivefox and @Mustang5L5. I will add that the few trained AC technicians I know typically use the weights as a guideline but often adjust the amount added based on pressure readings vs ambient temp and based on temp coming from the vents. My car has custom AC lines that are longer than stock so when mine was filled, the weight was just a guideline to get us close, then pressures and temp were used to fine tune the amount of refrigerant in the system.
 
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I will add that the few trained AC technicians I know typically use the weights as a guideline but often adjust the amount added based on pressure readings vs ambient temp and based on temp coming from the vents.
That's correct. You use the weight as a guideline but need to use the pressure readings when you are close.

What ultimately affects how much refrigerant to add is the internal volume of the system, and this can be affected by things like having too much, or too little oil, or things like custom lines which might be a little shorter/longer depending on routing.

For example, when i did my fox system i used a modern parallel flow style condenser and scrapped the OEM serpentine style. These condensers have slightly less internal volume, so rather than the recommended 40 oz of refrigerant required, i only had to charge 36 oz to get it to where it needed to be,
 

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Discussion Starter · #28 ·
I agree. knowing the ambient conditions are critical because the pressures will vary. If the outside temp was higher, i would suspect not enough refrigerant based on those pressures. You really want to report pressures under max stress conditions. 1500+RPM, fan speed on high, doors open and report the pressures while still at 1500+ RPM

Cclaro, did you fill by weigh by using a scale, or just by estimating based on can volume?



Does spraying the condenser with water improve performance? That would signify an airflow issue, but your high side pressure doesn't seem high enough to support this.

I agree that your vent temps should be better. My 8-year old Taurus puts out vent temps in the low 40's at idle and will drop to 40 degrees once moving. My fox will do vent temps in the 35-38 degree range while just iding, but that's with a brand new fresh R-12 system.
Spraying with water does improve the vent temperatures. The cooler the ambient temperature the cooler the vent temps usually because the cabin temperature drops as well. We filled it by weight using a scale. I can check the low side once more to see the pressure now since it’s around 95° out
 

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Discussion Starter · #29 ·
So I did a couple things, low side pressure while running in 94° ambient temps is around 33 psi, I couldn’t check the high side my buddy has the proper gauge set so I could only look at the low side. I let the car run till operating temp on normal ac with the windows open and from 94° ambient temps (probably closer to 100 due to humidity) it was spitting out vent temps of about 67°. As I put it on Max ac the temps drop to around 63°. Cabin temps were just shy of 98 degrees. It wouldn’t get any cooler until I closed the windows and began to drive it around (just 15-20mph) and immediately the temps began to drop with just some airflow going through the front of the car. Driving around stop and go at those speeds I was able to see vent temps at around 57°. I’m sure higher speeds with longer periods of driving would’ve yielded some lower temperatures as well. I came back into the drive way with the car sitting at around 195° coolant temps and it was able to hold around a 62° Vent temp. I sprayed the condenser with a little bit of water and watched the temps drop to around 57.5. Windows up ac going with cabin temps at around 85° at this point. When I sit there at 1500 rpm for a couple of minutes the temperature will actually go up a bit as the compressor cycles due to me spraying it with water and dropping the pressures due to the temperature change considerably. When it heats back up the compressor will stop cycling and the vent temps will begin to drop from around 63° to 58°. It’s a 93° day with temps that feel like 103 and 55% humidity at the moment. It still sounds like an airflow issue and as mentioned before with the air not really blowing as hard as I feel it should possibly a dirty evaporator as well. I’d like to know what you guys think about the evaporator theory as well as the results discussed in this Post. Sorry about not being able to grab a high side reading, in a couple days I’m gonna get the gauges on again to check when it’s hot out to verify all pressures
 

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If it's 93 outside your low side should be between 45 and 55 psi, high side around 270ish . That tells me your refrigerant levels are low but you need to verify high side first.
 
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so would I forgo the addition of freon by weight and rely entirely on pressure alone? I saw someone mention that above but wasn't sure
You need to verify both high and low side to make sure both are reading low. If both are reading low you would add more refrigerant. I know you said your replaced the orifice tube. Anything else replaced and was your system leaking before you replaced parts? Did you add oil to the system?
 

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Discussion Starter · #34 ·
You need to verify both high and low side to make sure both are reading low. If both are reading low you would add more refrigerant. I know you said your replaced the orifice tube. Anything else replaced and was your leaking before your replaced parts? Did you add oil to the system?
new compressor, accumulator is less than a year old, condenser less than a year old. only items I haven't replaced are the lines (minus the liquid line containing the orifice tube) and the evaporator. we couldn't find any leaks with the dye in the bay so if there is a leak its gotta be the evaporator. I can verify pressures in a couple days I have some extra R134 I can add to the system
 

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new compressor, accumulator is less than a year old, condenser less than a year old. only items I haven't replaced are the lines (minus the liquid line containing the orifice tube) and the evaporator. we couldn't find any leaks with the dye in the bay so if there is a leak its gotta be the evaporator. I can verify pressures in a couple days I have some extra R134 I can add to the system
How much oil did you add? The new compressor usually comes with some oil but not enough for the whole system. Sometimes they have no oil. Do you know if yours had oil?
 

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Also when you replaced the compressor did you drain the old compressor to see how much oil was in it? That determines how much oil you add when replacing it.
 

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so would I forgo the addition of freon by weight and rely entirely on pressure alone? I saw someone mention that above but wasn't sure

At this point, you really can't. If you had the machine, you would recover the refrigerant, pull a vac and recharge again. Since you don't really have that, you need to switch to using pressures.

I don't think you need to add much more, but do agree with Dwain that you need a little bit more. However it's possible that's because you didn't have the proper level of oil in the system.

WOuld need to see high side pressures here to really tell you next steps. Remember, you want to take your readings over 1500 RPM with fan to max and the doors open (to avoid any recirculating air). The goal is to cool purely 90 degree (or whatever outside temp is) across the evap and no recirculated air.

I don't have an SN95 service manual in front of me but I beleive low pressure cutoff is around 20psi. When you hook up the manifold guages with high/low pressure guages, pay attention to the low side when it drops and note where the pressure cuts off. When it cuts out, note the high side pressure. If it's very high 300+PSI or more, that would suggest either a blocked orifice, or poor airflow across the condensor. If you spray water and it drops, you need more airflow.

If the low side cuts off at 20psi or so and your high side is sub 200psi on a hot day, you just need more refrigerant. In fact, on a hot humid day, that compressor shouldn't really cycle much at all. Should hold pretty well around 40-45psi and your high side should be 250-275ish.

You should be able to maintain 40-45 degrees vent temp at idle with doors open.

But I also do think you have an airflow issue through that condenser.


Good luck, as i will be away from internet for a few days
 
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I don't think you need to add much more, but do agree with Dwain that you need a little bit more. However it's possible that's because you didn't have the proper level of oil in the system.


Yep that's what i was getting at.
 
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Discussion Starter · #40 ·
At this point, you really can't. If you had the machine, you would recover the refrigerant, pull a vac and recharge again. Since you don't really have that, you need to switch to using pressures.

I don't think you need to add much more, but do agree with Dwain that you need a little bit more. However it's possible that's because you didn't have the proper level of oil in the system.

WOuld need to see high side pressures here to really tell you next steps. Remember, you want to take your readings over 1500 RPM with fan to max and the doors open (to avoid any recirculating air). The goal is to cool purely 90 degree (or whatever outside temp is) across the evap and no recirculated air.

I don't have an SN95 service manual in front of me but I beleive low pressure cutoff is around 20psi. When you hook up the manifold guages with high/low pressure guages, pay attention to the low side when it drops and note where the pressure cuts off. When it cuts out, note the high side pressure. If it's very high 300+PSI or more, that would suggest either a blocked orifice, or poor airflow across the condensor. If you spray water and it drops, you need more airflow.

If the low side cuts off at 20psi or so and your high side is sub 200psi on a hot day, you just need more refrigerant. In fact, on a hot humid day, that compressor shouldn't really cycle much at all. Should hold pretty well around 40-45psi and your high side should be 250-275ish.

You should be able to maintain 40-45 degrees vent temp at idle with doors open.

But I also do think you have an airflow issue through that condenser.


Good luck, as i will be away from internet for a few days
Very helpful post thank you
 
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