gjohnson

iTrader: (4)

Ok, so I'm trying to diagnose my AC issue and I'm looking for some opinons. Here's the deal, I have a LSX swap and I'm running a 2004 GTO AC compressor. I was told the compressor had around 10,000 miles on it when it was pulled from the GTO, but I have no way of verifying this. I'm running the 240sx condenser and drier, and custom AC lines with a GM AC pressure sensor and electric fans. The PCM controls the fans when the AC is turned on and right now I have them both set to run on high when the AC is turned on.

Of course the car cools great when the temps are low around 80's or below, but on hot days I get nothing but hot air out of the vents unless I'm crusing at highway speeds. Even at highway speeds the air is blowing around 60* from the vents on a 95* day. At idle it blows more like 76*.

Tonight I hooked up some gauges to the system, because I was thinking the freon might be low, but after inspecting my pressures I'm not sure what to think. At 1000 Rpms my Low side is sitting at about 60 psi and the High side is at 200 psi. Now, when I check the FSM it tells me that if the high side is low and the Low side is high, replace the compressor. Does this sound like the issue?

Now as another issue, when I was pulling the engine last time a bolt that was holding my hoist chain broke and the engine dropped some. When it did, it bent both of the AC lines down at the firewall, which I tried bending back up and correcting. Looking over my setup with my neighbor, he thinks the expansion valve could be giving me issues or it could be the compressor. Any ideas???? I don't know if it makes a diffrence, but my car did sit for at least 4 years before I picked it up, so I don't know if that could have added to more issues. Thanks for any input.

bczee

iTrader: (12)

I am no expert. .but..

Seem like you have a bit too much low pressure side.. what is the spec for the 240 system ?

My general rule of thumb is about 40-45 psi on the low (or less, depending on the system). should be close to the inside blowing temp (?). If the outside temp is around 95.. I would expect to see his side around 215-220 psi

but this all depends on the system.

Also. one issue could be the Compressor. (i have this issue myself). The Compressor could be a Variable displacement unit vs a Fix displacement compressor. if so.. it will only default to 80% of capacity and have not way to dynmically go to 100%. There is a way to weld up the inside of the compressor to be pumping at 100% all of the time.

there has been a thread on the how to do this.
https://ls1tech.com/forums/conversio...ble-fixed.html

But you might talk to a AC shop who know about both systems. Let me know what you find.

BC

G-Body

iTrader: (4)

Could be either, I would check the expansion valve (IIRC its also called an orfice tube ) first because they are dirt cheap and it could have been damaged when the lines were bent if it was close to the bend.

gjohnson

iTrader: (4)

The FSM shows with an Ambient Air temp of 95*(F) high side pressure should be between 202 - 245 psi and low side pressure should be between 23 - 38 psi.

Yeah I think I may inspect the expansion valve first, but I don't know how to tell if it's good or bad.

How do I find out if a 04 or 05 GTO AC compressor is fixed or variable?

01ssreda4

iTrader: (96)

Low side pressure is definitely higher then all the working ac systems I have messed with.

DWillTA

iTrader: (3)

With the system running and gauges connected take some temp readings first at the outlet of the condenser and second at the accumulator/evaporator outlet. See how those temps compare to your pressure readings. You are checking subcooling at the condenser and superheat at the accumulator/evaporator outlet.

Did you charge the system? If not, the first thing I would do is evacuate the system and weigh in the correct charge. It could be as simple as an overcharge condition or a contaminated charge (ie mixture of refrigerants).

The temp readings will tell you alot about what is actually going on in the system.

2xLS3

iTrader: (3)

As far as the system being contaminated by not being evaculed well enough or mixed refrigerant being the system, normally when this happens, the high pressure gets extremely high, which isn't the issue here. I will add that most of my HVAC experiance is comsercial and not automotive, but the principal and theory in their operation is the same.

Low pressure being too high is normally a sign of too much flow through the system or not enough flow through the compressor. It can't be the orfice or TX valve being blocked, since either of those conditions would would cause excessive high side pressure and lower low side pressure. The conditions that would cause the low side to be high, would be a stuck open TX valve or a missing orfice tube, or the compressor not pumping enough refrigerant

99427camaro

iTrader: (1)

just something you might have over looked, are you under driven, also how much 134 did you put in, and when you checked the psi what was the temp out side and was the car up to temp, are you getting any icing anywhere, one more idea is to check the in coming temp on the condensed and the outgoing, from there if you have a scanner you can take your compressor and turn it on 100% to make sure your computer is not under running it, i have run in to this before where the computer will keep kicking the ac clutch on and off because of a bad high pres sensor

gjohnson

iTrader: (4)

Ok, I've been reading over some of the variable displacement info that I could find and I'm wondering if that could be the issues like bczee said above. Does anyone have info on from the GTO FSM that would diagnose abnormal pressure diffrences with the AC system. My system may even been over charged because I wasn't aware the variable displacement compressors operate at lower Low side psi numbers than I've charged before.

Hodge

iTrader: (2)

Got out a PT chart (134a):

Low side at 60 psi = 62 degF saturated
high side at 200 psi = 132 degF saturated

Low side is HIGH!!! and high side is probably a little low (but I don't know what the ambient temp was when you took these pressures). I don't know if your 240sx was originally R-12 or R-134a. If it was R-12, you probably need a better condenser (more fins per inch and/or more face area) and better airflow over the condenser. HOWEVER when the low side is high and the high side is low, I suspect something is going on with your compressor. I am not familiar with the late model variable displacement compressors. My speciality is residential HVAC. for what it is worth, I would expect the normal Low side to produce an evaporator temp of 32 to 40 degF (unless it is really hot outside; above 95 degF). those evap temps have a pressure range of 27 to 35 psi.

gjohnson

iTrader: (4)

Ambient temp was 96* when got these numbers. My 240sx was originally R-134a.

2xLS3

iTrader: (3)

Compressor
The Delphi V7 compressor can match the air conditioning demand under all conditions without cycling. The basic compressor mechanism is a variable angle wobble-plate with 7 axially oriented cylinders. The compressor has a pumping capacity of 179 cc.

The control valve is installed in the compressor rear head. The wobble-plate angle of the compressor, and the resultant compressor displacement, are determined by the compressor crankcase to suction pressure differential which is governed by the control valve.

When the A/C capacity demand is low, the crankcase pressure behind the pistons is equal to the pressure in front of the pistons. This forces the wobble plate to change its angle to towards vertical which reduces the stroke of the pistons and reduces the output of the compressor to approximately 14.5 cc. The evaporator cooling load is reduced, ambient temperature or blower fan speed is reduced, and therefore, the suction pressure is reduced until it reaches the control point. To reach the control point, the bellows in the control valve assembly has expanded to allow discharge pressure to bleed past the control valve ball valve seat and into the compressor crankcase. This crankcase pressure acts as an opposing force behind the compressor pistons to cause the wobble plate to change its angle towards vertical and therefore, reduce piston stroke.

When the A/C capacity demand is high, the crankcase pressure behind the pistons is less than the pressure in front of the pistons. This forces the wobble plate to change its angle away from vertical which increase the stroke of the pistons and increases the output of the compressor to approximately 164 cc. When suction pressure is above the control point, it will compress the control valve bellows. This will close off the discharge valve as the ball valve is now on its seat. The shuttle valve moves towards the suction port and opens the suction valve. Crankcase pressure will then bleed from the compressor crankcase past the suction valve to the suction port. As the crankcase pressure behind the pistons is reduced, the wobble plate will tilt from vertical causing the pistons to move towards maximum stroke. The compressor will then have a corresponding increase in its displacement.

2xLS3

iTrader: (3)

A/C Cycle
Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automotive use. R-134a is a very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.

The A/C system used on this vehicle is a non-cycling system. Non-cycling A/C systems use a high pressure switch to protect the A/C system from excessive pressure. The high pressure switch will OPEN the electrical signal to the compressor clutch, if the refrigerant pressure becomes excessive. After the high and the low sides of the A/C system pressure equalize, the high pressure switch will CLOSE. This completes the electrical circuit to the compressor clutch. The A/C system is also mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continues to rise, the high pressure relief will pop open and release refrigerant from the system.

The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat. The refrigerant is discharged from the compressor through the discharge hose, and forced through the condenser and then through the balance of the A/C system.

Compressed refrigerant enters the condenser at a high-temperature, high-pressure vapor state. As the refrigerant flows through the condenser, the heat is transferred to the ambient air passing through the condenser. Cooling causes the refrigerant to condense and change from a vapor to a liquid state.

The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line to the thermal expansion valve (TXV).

The TXV is located at the evaporator inlet. The TXV is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the TXV, the pressure on the refrigerant is lowered, causing the refrigerant to vaporize at the TXV. The TXV also measures the amount of liquid refrigerant that can flow into the evaporator.

Refrigerant exiting the TXV flows into the evaporator core in a low-pressure, liquid state. Ambient air is drawn through the HVAC module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant to boil inside the evaporator core. The boiling refrigerant absorbs heat from the ambient air and draws moisture onto the evaporator. The refrigerant exits the evaporator through the suction line and flows back to the compressor in a vapor state, completing the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.

The conditioned air is distributed through the HVAC module for passenger comfort. The heat and moisture removed from the passenger compartment condenses, and discharges from the HVAC module as water.

2xLS3

iTrader: (3)

A/C Pressure Sensor Operation

Low Pressure Cut Out 180 kPa (2600 psi)

Low Pressure Cut In 240 kPa (35 psi)

High Pressure Cut Out 2900 kPa (420 psi)

High Pressure Cut In 2000 kPa (290 psi)

1st Stage Fan Operation On 1517 kPa (220 psi)

1st Stage Fan Operation Off 1214 kPa (176 psi)

2nd Stage Fan Operation On 1758 kPa (255 psi)

2nd Stage Fan Operation Off 1517 kPa (220 psi)




Filter Drier
The filter drier receiver acts as a particle filter, refrigerant storage container and most importantly a moisture absorber. Moisture, temperature and R-134a causes hydrofluoric and hydrochloric acid. The silica gel beads (desiccant) located in the filter drier receiver absorb small quantities of moisture thus preventing acid establishment.

Thermal Expansion Valve (TXV)
The thermal expansion valve (TXV) controls refrigerant gas flow to the evaporator and ensures that complete evaporation takes place. It has 2 refrigerant passages. One is in the refrigerant line from the condenser to the evaporator and contains a ball and spring valve. The other passage is in the refrigerant line from the evaporator to the compressor and contains the temperature sensing element.

TXV Opening
As the non-cooled refrigerant from the evaporator core flows through the TXV outlet (suction), it makes contact with the underside of the thin metallic diaphragm and reacts on the refrigerant contained above that diaphragm. This refrigerant then expands forcing the pin downwards moving the ball off its seat, compressing the spring and allowing more refrigerant to enter the evaporator.

TXV Closing
Operation is similar to opening but now the refrigerant from the evaporator is cold. The refrigerant contained above the diaphragm now contracts. The ball moves towards the seat aided by the compressed spring, reducing refrigerant flow. Low pressure liquid R-134a passing through the evaporator should be completely vaporized by the time it reaches the TXV outlet side. The TXV is installed in the engine bay to the right side of the instrument panel.

Hodge

iTrader: (2)

Seems the consensus is something going on with the compressor. I agree but can offer no more insight.