Need some help. My A/C works but seems a little weak. I checked the specs for A/C low side and manual states the following.

For Ambient Temp of 80F: 36 - 59 psi
For Ambient Temp of 90F: 41 - 69 psi

For my test, the outside temp was ~84F and my low side psi was 38 psi. I know per the 80F it is within spec by 2 psi, but its out of spec for 90F. Since it was 84F, not sure if I should split the difference and call 38 psi just barely in spec. What do you think? Does it seem to low? If so, should I add more R134A and what psi do you think is recommended on the low side for my test?

Thanks for any help

 

Your math is correct, IF the extrapolation is linear.
Since you (and I) have some doubt, and it is hovering on the low side, get it pumped up to well within limits and see if it makes a difference.

 

I would not go by the ourdoor air temp as it does not depict what the pressure is supose to be doing.If your entering air(inside the Jeep) is high so will the suction pressure. You would have to check your superheat to be sure that your charge is about right. For that you would need a PT chart(Pressure Temprature chart) Or look on your actual gauges and they have the chart on them(all i have seen have had them on the dial).38# has a saturation temp of about 44 deg F, so you would take your temp of your suction line(the cold one) lets say its 56 deg F. Subtract 56 from 44 and you would get 12 deg superheat.
Now if it is rather cool outside your suction superheat would be lower,same effect if you were to slow down the fan or had a dirty coil. This is why they run accumulators so you would not trash a compressor if you turned the fan to low. I do not know what the exact design specs are but generaly speaking superheat should be somewhere between 10-14 possibly even 16.

 

I always check the charge with the doors and windows open, fan on high speed, and recirulate on. You want the idle pressure to be high enough to be above freezing (36.8 psi = 32degrees) but traveling down the road with a high heat load the pressures will pull down into the mid 20's. A great way to make sure you have enough freon but not overcharged is to tape the guages up on the windshield and then drive around with a digital thermometer in the vents. You can then adjust the charge to achieve lowest temp............

 

The procedure in the factory maintenance manual is nothing like what you describe. It even has ambient temperature as a factor, which must be above 70 F when performing the pressure/temperature tests. It makes no mention of superheat.

This quote is closer to what the service manual says.

I am just wondering why the first quote is so far from what the manual says.

 

If there is not a given RPM for the spec, it's pretty useless. Since the spec is such a low reading, I would take for granted it is supposed to be read at idle. Does it specify?

 

Because that is typically how you would charge a unit that does not have a Thermostatic Expantion Valve. When you have a fixed Orfice that is how you charge it.You take it to the extreme conditons at which it is designed and chearge it to those specs

 

It specifies test at idle and normal operating temp.

Here is the procedure from the service manual:

A/C PERFORMANCE
The A/C system is designed to provide the passenger compartment with low temperature and low humidity air. The A/C evaporator, located in the HVAC housing is cooled to temperatures near the freezing point. As warm damp air passes over the fins of the A/C evaporator, the air transfers its heat to the refrigerant in the evaporator coils and the moisture in the air condenses on the evaporator fins. During periods of high heat and humidity, an A/C system will be more effective in the Recirculation mode (max-A/C). With the system in the Recirculation mode, only air from the passenger compartment passes through the A/C evaporator. As the passenger compartment air dehumidifies, the A/C system performance levels rise.

Humidity has an important bearing on the temperature of the air delivered to the interior of the vehicle. It is important to understand the effect that humidity has on the performance of the A/C system. When humidity is high, the A/C evaporator has to perform a double duty. It must lower the air temperature, and it must lower the temperature of the moisture in the air that condenses on the evaporator fins. Condensing the moisture in the air transfers heat energy into the evaporator fins and coils. This reduces the amount of heat the A/C evaporator can absorb from the air. High humidity greatly reduces the ability of the A/C evaporator to lower the temperature of the air.

However, evaporator capacity used to reduce the amount of moisture in the air is not wasted. Wringing some of the moisture out of the air entering the vehicle adds to the comfort of the passengers. Although, an owner may expect too much from their A/C system on humid days. A performance test is the best way to determine whether the system is performing up to design standards. This test also provides valuable clues as to the possible cause of trouble with the A/C system. The ambient air temperature in the location where the vehicle will be tested must be a minimum of 21° C (70° F) for this test.



A/C PERFORMANCE TEST
WARNING: Refer to the applicable warnings and cautions for this system before performing the following operation (refer to 24 - HEATING & AIR CONDITIONING/PLUMBING - WARNING) and (refer to 24 - HEATING & AIR CONDITIONING/PLUMBING - CAUTION). Failure to follow the warnings and cautions could result in possible personal injury or death.

NOTE: When connecting the service equipment coupling to the line fitting, verify that the valve of the coupling is fully closed. This will reduce the amount of effort required to make the connection.

NOTE: The work area ambient temperature must be above 21° C (70° F) and the evaporator temperature must be above 13° C (55° F) prior to conducting the A/C Performance Test.


1. Check for diagnostic trouble codes using a scan tool. If no DTCs are found in the powertrain control module (PCM) or engine control module (ECM) (depending on engine application) or the totally integrated power module (TIPM), go to STEP 2. If any DTCs are found, repair as required, then proceed to STEP 2.
2. Connect a tachometer and a manifold gauge set or an A/C recycling/charging station.
3. Operate the heating-A/C system under the following conditions.
Engine at idle and operating temperature
Doors or windows open
Transmission in Park or Neutral with parking brake set (depending on application)
A/C-heater controls set to Recirculation mode (max-A/C), full cool, panel mode, high blower and with A/C compressor engaged. If the A/C compressor does not engage, see the A/C System Diagnosis chart.

4. Insert a thermometer in the driver side center panel air outlet and operate the vehicle a minimum of ten minutes to allow the thermometer temperature to stabilize.
5. With the A/C compressor clutch engaged, compare the air temperature at the center panel outlet and the A/C compressor discharge pressure (high side) to the A/C Performance Temperature and Pressure chart. The compressor clutch may cycle, depending upon the ambient temperature and humidity. If the clutch cycles, use the readings obtained before the clutch disengaged.

A/C PERFORMANCE TEMPERATURE AND PRESSURE

(insert by ronjenx: below, all the A's go together, B's go together, etc.)

Ambient Temperature
A... 21° C (70° F)
B...27° C (80° F)
C...32° C (90° F)
D...38° C (100° F)
E...43° C (110° F)


Air Temperature at Center Panel Outlet
A...6 -15° C (42 - 59° F)
B...7 -18° C (45 - 64° F)
C...9 - 21° C (48 - 69° F)
D...11 - 22° C (52 - 72° F)
E...13 - 24° C (56 - 75° F)


A/C High Side Pressure
A...1034 - 1896 kPa (150 - 275 psi)
B...1207 - 2068 kPa (175 - 300 psi)
C...1379 - 2241 kPa (200 - 325 psi)
D...1551 - 2413 kPa (225 - 350 psi)
E...1724 - 2241 kPa (250 - 375 psi)

A/C Low Side Pressure
A...214 - 365 kPa (31 - 53 psi)
B...248 - 407 kPa (36 - 59 psi)
C...283 - 476 kPa (41 - 69 psi)
D...317 - 483 kPa (46 - 70 psi)
E...359 - 496 kPa (52 - 72 psi)



6. If the air outlet temperature fails to meet the specifications in the A/C Performance Temperature and Pressure chart, or if the A/C compressor discharge pressure is high, refer to the A/C System Diagnosis chart.

 

I am not sure if you are saying our expansion valves are thermostatic or fixed.

Here is what the manual says about the expansion valve in the JK:

DESCRIPTION

The A/C expansion valve controls the amount of refrigerant entering the A/C evaporator. The A/C expansion valve is of a thermostatic expansion valve (TXV) design and consists of an aluminum H-valve type body (1) with an inlet port (2), outlet port (3) and an integral thermal sensor (4).

The A/C expansion valve is located between the A/C refrigerant lines and the A/C evaporator in the engine compartment.

 

I was Unaware that our wranglers have TXV's. And Quite frackly that is odd that is would be in it. Most residential ac's do not have a txv they mostly have flowraters (fixed Orfice).But being a TXV in a vehicle makes it very dificult to charge because that fact when you charge a System With a TXV you charge it by Subcooling. With the heat of the engine compartment make it hard to get a stable good reading.A TXV is a varible rate orfice that it controller off of a preset super heat that it tries to maintain (most are set to 12*f)