AC pressure specs?

[Red-Arrow]

OMG its been 7 months since I posted on this tropic because its hot again!

I went to Pepboys as they had the Ac manifold gauges which cost $50 to $250 buck. They could only connect one port next to the headlamp and it showed pressure in the range of 85 psi.

You know what Pepboys are like. " Sir you need to empty the system and refill it with new Freon" " It has pressure but no freon"

I was like whats the correct pressure for the system and they are like. " Its complicated" Implied you know nothing about cars!

Where can I get a cheap gauge from? I plan on venting some of the pressure. Maybe 35 psi to the atmosphere. Sound good?

[jblackburn]

Any auto parts store sells cans of R-134 with gauges attached to them.

Is your AC compressor cycling at all? If it was running as it should have been when they were testing it, you'd never seen 85 psi on the low-side port there.

[Red-Arrow]

I just bought a $12.99 gauge from Autozone and an 18 0z can with a second gauge. I let too much pressure out and had to refill

The compressor does not cycle unless I jump the switch with a paper clip like you suggested. This is how I got the new r134a in but its only showing 33psi now. How many Ounces should I put in the system? Should I go by pressure or weight?

I think its some kind of sensor problem but I'm not sure which one?

Can the grab handle temperature sensors stop the compressor?

Can the OBD1 port test for a fault?

[jblackburn]

It sounds like you have a bad pressure switch there, if it runs when you jump it. 33 psi is more than enough for it to stay on constantly.

Unfortunately, that means completely evacuating the system, replacing the switch, and then recharging it. That will have to be done by a shop with the proper equipment.

[Red-Arrow]

The pressure switch has a valve with an o ring under it. It allows gas out if I depress the pin. I have removed the pressure switch and tested a second hand valve from Ebay. It made no difference. This is driving me nuts.

Could I jump the connector with a fuse and just drive the car like this?

[kcodyjr]

I suspect that's why my compressor recently seized. That switch is there for a reason.

[burnout8488]

Have you tried shimming your A/C compressor clutch? That could be the issue. Use a feeler gauge on the clutch, measure, and report back with the findings.

[czar]

1995 Volvo 850 A/C SYSTEM SPECIFICATIONS

Compressor Type .................... Zexel DKS-15CH 6-cyl.

Compressor Oil Capacity ..................... (2) 6.8 ozs.
Refrigerant Capacity (R-134a) .................. 26.4 ozs.

High Side ............... 406-450 psi (28.5-31.6 kg/cm )
Low Side .................... 25-33 psi (1.8-2.3 kg/cm )

These are the pressures and capacities for the 1995 Volvo 850.
You may need to have your system evacuated and then filled to the correct pressure (25-33 psi).
you only get the correct pressure when the compressor is running.

[SimLyons]

I used jblackburn's advice and posting a month or so ago. My '97 850R was virtually emoty and my compressor would not cycle at all. After jumping the pressure switch and getting an initial fill of 25 psi or so I was able to run normally and continue the fill to 34 psi at 70 deg. ambient. It runs great now and puts out 40 deg F at the vent with A/C full on (checked with an A/C thermometer). So far no more leaks. I will recheck every few weeks through the summer.

BTW: I thought "freon" was obsolete/illegal. Isn't it just "refridgerant...R134a" now? I don't really know but I have been corrected a few times. Just wondering.

[jimmy57]

Pressure readings are not the way to do it on CCOT (cycling clutch orifice tube) systems. You can't just add refrigerant until you get that pressure. Temperature and humidity and engine speed all vary the pressures.
You can evacuate and then charge by weight or you can partial charge or charge from empty by monitoring temperature and low side pressure and cycling interval with the engine at high idle (1250-1500 rpm), fan on next to highest speed and recirc selected, the conditions Volvo and others call for for diagnosing A/C systems on cars and trucks.
The high side will not be nearly that high. The system has a high pressure cut out for compressor at about 430 psi.
High side may go 250-275 on a HOT HOT day for a brief time when interior is HOT or go higher than that if there is an airflow problem for condenser or a blockage like a clogged orifice filter screen.

When the system has run for a few minutes in the conditions above per Volvo methods, the vent temperature should be mid 40's if airflow over condenser is below 90F and high 40's to low 50's if ambient temp is high 90's to low 100's.
The low side will get into upper 20's and when car gets cooler inside it will cycle off compressor at 22-24 psi and then come back on when pressure on low side goes up to 42-45psi. IF you turn fan down one speed and it cycles on for 25-30 seconds on a upper 80's day and then turn it up a fan speed and cycling gets longer on period, maybe 60-70 seconds then charge is prefect. The right charge level will also be noted by distinctly chilly low side line all the way back to compressor.
The high side will be over 200 and after car cools down inside the high pressure will be 150-180 unless the ambient temp is upper 90's low 100's and then the high side may stay close to 200 or a bit higher.
Humidity has a bearing on the pressures too. High humidity makes air have higher specific heat and the system works harder and pressures will be slightly higher and cycling of compressor may be on a longer on interval with vent temps 2-3 degrees higher.
A/C systems using expansion valves (s80,s60, xc90, P2 v70 and xc70, 00-04 s40/v40) regulate the low side and to some degree the high side and charging by pressure monitoring is more reliable.