Pressures.

[Tim]

Respectfully I am going to ask what some are thinking are high pressures. I have seen many posts where there is a suggestion of high-pressure issues when it's listed even below 325psi. I personally think trying to achieve some specific high side number puts an unachievable thought in readers' minds. In my personal opinion, any high-side reading under 325 is fine. Each vehicle will have different operating pressures. We can remember back to the old R12 days, 325 psi was a normal operating range. IS a lower high-side reading better? Sure, but there has to be a reasonable understanding that 300/325 is not horrible overall. Anything above 300/325 should be a concern.

[DetroitAC]

I can't and don't make statements about what is an across the board high pressure. Need more information like how big are the compressor and condenser/fan relative to each other, and how much HVAC cooling load.

2000 Dodge Neon running 400 psig at idle 110F ambient, it's OK, normal.

2015 Silverado running 400 psig at idle, 80F ambient in Michigan, WTF! is there a garbage bag blocking your condenser?

[Tim]

I can't and don't make statements about what is an across the board high pressure. Need more information like how big are the compressor and condenser/fan relative to each other, and how much HVAC cooling load.

2000 Dodge Neon running 400 psig at idle 110F ambient, it's OK, normal.

2015 Silverado running 400 psig at idle, 80F ambient in Michigan, WTF! is there a garbage bag blocking your condenser?

Agreed. I just see some unreasonable pressure listings, IMO. 185 high-side is not happening in 100-degree ambient in a general sense.

[swampy 6x6]

hi
high side pressures for R12 were regularly at 150psi or lower in moderate weather . This would mean a refrigerant temperature of R12 /150psi= 117f in modern terms R134 / 170psi =117f . So r134a is about 20psi higher at same refrigerant temp .

Remember ALL things R12 operated refrigeration etc operated 120-160psi

Automotive benefits from a LARGE single or twin smaller condensers to achieve this.

******TXV valves need 100% liquid at low temp supplied to them to work properly . Having a to small condenser does not achieve this .

WHAT HAPPENS WHEN U SUPPLY HIGH TEMP LIQUID
answer --the evaporator uses some of its own BTU cooling capacity to lower this liquid to an operating liquid condition ,,,therefore consuming its own capacity to cool rather than devote it to cooling the cabin

is OVERCOOLING AN ISSUE
No , not when using 2 medium sized condensers
Why R134a will only cool down to ambient say 110f refrigerant temp at 150psi . This was experienced on a ambient day temp of 110f

Is SUBSCOOL A PROBLEM
NO
Install a sight glass charge to full /clear glass and measure sub-cool to make sure u have some .

High pressures .,...??? R134a
ideal 150--200psi under all cond.
acceptable 200--225
borderline 225 --250psi
over 250 not acceptable ,, but there are vehicles that have such poor cooling this is normal

250psi or higher compressors can start being noisey

[swampy 6x6]

hi
LOW pressure
ideally 20--35psi
Remember freezing is approx 30psi

There are exceptions eg Nippon Denso ,just 1x brand that operates lower . Remember evaporator design and air flow design can influence this .
Also the a/c units that run lower psi -temps nearly always run an electronic thermister as a thermostat . Old school mechanical thermostats would be so inaccurate that freezing was always a very very high risk if running low psi /temps in evap .

Personal opinion I really like block TX valves ,,why ,, the internal equalization sensing is highly reactive . U can see this on the low gauge movement .

[Tim]

150/200psi high side, maybe in January.

[bohica2xo]

Tim:

I use the ambient factor to evaluate a system.

Biggest problem is testing parameters. Constant issue here on the forum, with people posting idle speed pressures.

With the doors open, cabin fan on highest speed and engine RPM above 1800 I look for the high side to be

Between 2.4 to 2.7 times ambient temperature. I see those pressures as "normal" for 134a

If it is 112f outside I fully expect to see 300+ PSI on the high side. If I see anything less than 265 PSI, I begin to think the compressor is tired.

If I see much over 2.7x under load test, I start with the condenser and airflow.


Detroit:
All of the Neons around here are running 2-60 air conditioning, because the cost of the repair exceeds the value of the vehicle. Most of them are uninsured for the same reason...

[Tim]

ACData1p.png (52.14 KiB) Viewed 4443 times

[bohica2xo]

Interesting. That chart supports my feeling that 3.0 x ambient is a maximum pressure.

Which vehicle is that?


.

[Tim]

20 Escalade

I just found this going through old files on my systems. The main point in me starting this thread is there is no magic pressure reading to achieve. We can't always say your high is too high at 210psi. When we do not know the variables, we could lead someone to try and achieve an impossible number. That is not to say bad advice has been given!