AC Pressures within spec but not cooling sufficiently. :-(

[BRIANGEE]

So I have this 2003 Exp that appears to be operating within it's specs for AC but is not cooling sufficiently.

High side = 217psi
Low side = 62 psi
Ambient Temp = 100F
Vent temp = 70f

According to Ford's service manual this is within the normal operating ranges. According to SOME online charts this is also acceptable however I've found quite a few common charts that state the high side should be more in the 340 psi range.

If the 340 psi value is correct it would seem the compressor is a little weak perhaps?

What do you all think?


P.S. The system is currently charged to factory spec of 54 oz for a front and back AC system. I made sure it was charged to spec prior to further diagnosing.

 

[stamp11127]

According to the charts the low side pressure is a little high and the high side pressure is low.

Any work been done to it recently - system opened up?
Oil added/removed?
AC Pro ever been added?
Working in the shade or out in the sun?

 

[BRIANGEE]

Any work been done to it recently - system opened up?

Yes, for recharge. System vacuumed, and refilled with factory specified charge by weight.

Oil added/removed?
No.

AC Pro ever been added?
Unknown.

Working in the shade or out in the sun?
The pressures measured were on an overcast day.

 

[docraymund]

Try cleaning the evaporator coils. Your high side pressure is ok because it's 2 to 2.5 times the ambient temperature.

 

[Hamfisted]

Honestly it sounds like a lame compressor. My '03 has a low side of 40 and high side of 250-300 psi at 90 degrees ambient. It's the original compressor, no leaks. Do you know if yours is the original compressor? Or what started this AC project in the first place ?


-Mike

 

[BRIANGEE]

leaks. Do you know if yours is the original compressor? Or what started this AC project in the first place ?


-Mike

Just bought this used... owner said he changed the compressor out 5 years ago. So I bought it rolling the dice that it was just undercharged.

 

[BRIANGEE]

Holding a rev at 1500 rpm's the pressures become:

45 low
250 high

 

[SMichaelG2]

Does it get cold at first, then gets warm? Could be the heater core valve staying open. I would feel the return line from the evaporator and see if it is cold. You also could have a faulty expansion valve. Are both ACs running hot?

 

[Hamfisted]

Holding a rev at 1500 rpm's the pressures become:

45 low
250 high

That's a little better. Is neither the front or back unit putting out cold air? Feel the evaporator piping and see if it's cold. If neither unit is cold just give it a little more freon and see how it does. Does the compressor look like it's been replaced ? Is there dye in the system, where you can look for leaks with a black light ? The hot water valve needs vacuum to stay closed. If the vacuum is taken away the valve opens. Make sure that the vacuum line to the hot water valve is in fact connected and there's vacuum on it when you're asking for cold air.


-Mike

 

[BRIANGEE]

Front and back put out a steady 72F at it's best. Suction line is cool to the touch.

When I switch to heat the blend doors activate fine and I only get heat. Would the vacuum line still be suspect?
I'm not sure where the heater core vacuum line is... is that the 2nd vacuum line that enters the passenger side firewall (next to the line that controls the main front vents / defrost blend doors?).

To the other questions:

Yes, previous owner replaced the compressor five years ago. Yes there is dye in the system. No leaks. The system holds a vacuum.

 

[Hamfisted]

The hot water valve vacuum line is the second line out of the firewall. The other line is the vacuum supply line TO the panel controlled module (located under the dash, in front of the center console...). If you're only getting 72 degrees at the evap lines I'm thinking it's just a little low on freon still.


-Mike

 

[stamp11127]

Part of your problem may be the previous owner added oil to the system when it didn't need any. Some of the "wonder ac cans" contain ac stop leak, oil and r134a. If there is too much oil already in the system and you charge by weight you end up overcharging the system. Guess what the result is - higher than normal pressures which equal higher than normal temps.

Also make sure the fan clutch is operating correctly and that the condenser and radiator are not clogged with debris. Doesn't hurt to wash them down with a low pressure sprayer or garden hose.

When teach charging by weight and pressures at the same time. Initial charge is at 80%, check pressures then add as necessary up to oem specs if needed. Autos low side usually runs about 35psi, high side 175—200 psi. Big trucks - semi, usually run higher on the high side, up to 300 psi. Ambient temps lately are in the low 90's here west of Atlanta. One reason for the higher pressure is that the evap on the big truck needs more refrigerant in the evap due to the larger cabin area. More refrigerant changing state equals more heat out of the cabin.

With the r134a refrigerant the pressure readings are very close to the respective component air temp that is leaving it. In your reply above the air temp at the evap would be 45 degrees leaving the plenum box. Probably close to 60 leaving the vent.

As systems lose refrigerant the low side pressure will drop, so does the the air temp leaving the evap. As a test for the students we deliberately under charges a ac tester we have in the shop. Evap pressure & temp was at 20 degrees. Nice and cold until it turned into an ice cube.