AC question

[jsbihn]

Ok so I just picked up my truck from getting the AC fixed. Here is the run down
New compressor
New Dryer
New tube
new freon
New Belts
ac was flushed

I get in the truck and turn it on, and it blows cool
not cold... cool

So I am thinking it might be the air from the outside but it is a little cooler then that.
Then I drive it a little, it gets colder... but definitely not like it did before the compressor went out.

Ok, now I drive it around 50 for a few minutes and it starts to get colder. Definitely is working but it seems that ever time I slow down or something the AC doesnt blow fridgid like it did prior to the compressor going out.

I am wondering if there could be an air bubble in the system
does that stop it from cooling
Or could there be a leak or something?

Given it was night time out when I tested this and tomorrow I am driving it in the heat
I am just wondering what you guys might think is going on

[VegasMike]

Doesn't it have something to do with the fact that the Hummer runs an engine mounted fan instead of electric fans? Basically what happens is when you slow down or stop, the rate of airflow through the a/c system slows, so it doesn't cool as much.

I notice with mine that when I stop, the system wars up a little, but once I get moving it cools back down.

[pdxrealtor]

It will fluctuate a little due to the mechanical fan, as VM stated.

Grab a temp gun and see how cold, or warm, the air coming out is. I forget what a car A/C is supposed to be but Google can tell you real quick.

[glennf1]

I noticed on mine sometimes it does the same thing and if I turn the temp all the way hot and then all the way cold it will get much colder. I thought the blend door was sticking but it will do it on both sides so maybe it needs to be calibrated or something.

[jsbihn]

I guess what I am really asking is why isnt it as cold as it was before the breakdown?

I mean is there something that could have been done or not done that is causing the AC not to be as cold as it used to be?

[jsbihn]

OK, here is the latest
- Today ... driving into work I noticed the AC cycles.
After driving for a long time, I noticed that the entire time it went from cold to cool and back to cold again...

Basically it will blow ice cold air , and then it will blow cool air.... then cycles again. You can actually feel and notice the temp change

I dont remember it doing that before the compressor broke.
So what do you think is going on ?
I would really appreciate any answers because I want to be able to take it back with knowledge so I dont get the "oh its suppose to do that" response

[pdxrealtor]

If no one chimes in call a couple other a/c shops and compare answers to your questions. That will arm you with the knowledge you need.

I have no idea whats going on. Could it possibly be your temp control is metering the air temps to keep the cabin at the specified temp on the thermostat?

[glennf1]

My compressor cycles too, it IS supposed to do that. Maybe they didn't put enough refrigerant in the system??

[[__--MUD--__]]

Interesting...looking at the diagrams for the ac. Each side (driver/pass) reads off the ambient light sensors to factor in sunload in the climate control.

I gotta ask why did you replace so many components? If the shop said all that was needed, I'd go someplace else and get a second opinion on your ACs current operation.

-----------------------
AIR TEMPERATURE DESCRIPTION AND OPERATION
The air temperature controls are divided into 5 areas:
- HVAC Control Components
- Heating and A/C Operation
- Automatic Operation
- Engine Coolant
- A/C Cycle
HVAC CONTROL COMPONENTS

HVAC Control Module
The HVAC control module is a class 2 device that interfaces between the vehicle operator and the HVAC system to maintain air temperature and
distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery
positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle
mode master, provides a device on signal.
The control module supports the shown features:

Air Temperature Actuator
The air temperature Actuators are a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference,
control, 5 volt reference and position signal circuits enable the Actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to
command the actuator movement. When the Actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the
actuator movement in. opposite directions. When the actuator shaft rotates, the potentiometers adjustable contact changes the door position signal
between 0-5 volts.
The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count
range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that
the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the
position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

Air Temperature Sensors
The air temperature sensors are a 2-wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors:
- Ambient air temperature sensor
- Inside air temperature sensor assembly
- Upper left air temperature sensor
- Upper right air temperature sensor
- Lower left air temperature sensor
- Lower right air temperature sensor
A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance
decreases. The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40?C (-40?F) to
+101?C (+215?F). The sensor signal varies between 0-5 volts.
The input of the duct air temperature sensors are different from the ambient and inside sensors. The HVAC control module converts the signal to a
range between 0-255 counts. As the air temperature increases the count value will decrease.
If the HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted air temperature value. The
default value for the ambient and inside air temperature sensors will be displayed on the scan tool. The default value for the duct air temperature
sensors will not be displayed on the scan tool. The scan tool parameter for the duct air temperature sensors are the actual state of the signal circuit.
The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.

Sunload Sensor Assembly
The sunload sensor is a 2-wire photo diode. The vehicle uses left and right sunload sensors. The two sensors are integrated into the sunload sensor
assembly. Low reference and signal circuits enable the sensor to operate. As the light shining upon the sensor gets brighter, the sensor resistance
increases. The sensor signal decreases as the resistance increases. The sensor operates within an intensity range between completely dark and bright. The sensor signal varies between 0-5 volts. The BCM converts the signal to a range between 0-255 counts. The BCM sends a class 2 serial data
message to the HVAC control module for automatic temperature calculations. The sunload sensor provides the BCM a measurement of the amount of
light shining on the vehicle. Bright, or high intensity, light causes the vehicles inside temperature to increase. The HVAC system compensates for the
increased temperature by diverting additional cool air into the vehicle.
If the BCM detects a malfunctioning sensor, then the control module software will use a defaulted sunload value. This value will not be displayed on
the scan tool. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition
is fixed. The scan tool parameter for the sunload sensor is the actual state of the signal circuit.

A/C Refrigerant Pressure Sensor
The A/C refrigerant pressure sensor is a 3 wire piezoelectric pressure transducer. A 5 volt reference, low reference, and signal circuits enable the
sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When
the A/C refrigerant pressure is high, the signal value is near 5 volts. The PCM converts the voltage signal to a pressure value.
The A/C refrigerant pressure sensor protects the A/C system from operating when an excessively high pressure condition exists. The PCM disables
the compressor clutch if the A/C pressure is more than 2957 kPa (429 psi). The clutch will be enabled after the pressure decreases to less than 1578
kPa (229 psi).

A/C Low Pressure Switch
The A/C low pressure switch protects the A/C system from a low pressure condition that could damage the A/C compressor or cause evaporator
icing. The
HVAC control module applies 5 volts to the A/C low pressure switch signal circuit. The switch will open when the A/C low side pressure reaches
124 kPa (18 psi). This prevents the A/C compressor from operating. The switch will then close when A/C low pressure side reaches 275 kPa (40
psi). This enables the A/C compressor to turn back ON.

HEATING AND A/C OPERATION
The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove
humidity from the interior and reduce windshield fogging. The vehicle operator can determine the passenger compartment temperature by adjusting
the air temperature switch. The vehicle passenger can offset the passenger temperature as much as 16.7?C (30?F). Regardless of the temperature
setting, the following can effect the rate that the HVAC system can achieve the desired temperature:
- Recirculation Actuator setting
- Difference between inside and desired temperature
- Difference between ambient and desired temperature
- Blower motor speed setting
- Mode setting
The control module makes the following actions when automatic operation is not selected, and an air temperature setting is selected:
- When the air temperature switch is placed in the warmest position, the control module commands the air temperature door to divert maximum air
past the heater core.
- When the air temperature switch is placed in the coldest position, the control module commands the air temperature door to direct air to bypass
the heater core.
- When the air temperature switch is placed between the warmest and coldest positions, the control module monitors the following sensor inputs to
determine the air temperature door position that diverts the appropriate amount of air past the heater core in order to achieve the desired
temperature:
- Sunload
- Duct temperatures
- Ambient temperature
- Inside temperature

[[__--MUD--__]]

The A/C system can be engaged by either pressing the A/C switch or during automatic operation. The HVAC control module sends a class 2 message
to the power train control module (PCM) for A/C compressor engagement The PCM will provide a ground for the A/C compressor relay enabling it
to close its internal contacts to send battery voltage to the A/C compressor clutch coil. The A/C compressor diode will prevent a voltage spike,
resulting from the collapse of the magnetic field of the coil, from entering the vehicle electrical system when the compressor is disengaged.
The following conditions must be met in order for the A/C compressor clutch to turn on:
- The ambient air temperature above 4°C (40°F) The A/C low pressure switch signal circuit is grounded
- The A/C refrigerant pressure sensor parameter is less than 2957 kPa (429 psi).
- The PCM receives an A/C request from the HVAC control module
- The engine coolant temperature (ECT) is less than 121°C (250°F).
- The engine rpm is more than 550 rpm
- The throttle position is less than 100%.
The HVAC control module monitors the A/C low pressure switch signal circuit. If the voltage signal on this circuit has no voltage drop the module will interpret this condition as a low pressure, disabling the A/C request. The A/C low pressure switch will open its internal contacts at 151 kPa (22 psi). Then close the contacts at 275 kPa (40 psi) to resume A/C operation. This switch assists in cycling the A/C compressor and prevents A/C compressor operation if system has a low refrigerant level. The PCM monitors the A/C refrigerant pressure sensor signal circuit. The voltage signal on this circuit is proportional to the refrigerant pressure inside the A/C high side pressure line. As the pressure inside the line increases, so does the voltage signal. If the pressure is above 2957 kPa (429psi), the A/C compressor output is disabled. When the pressure lowers to 1578 kPa (229 psi), the PCM enables the compressor to operate.
The sensor information is used by the PCM to determine the following:
- The A/C high side pressure
- An A/C system load on the engine
- An excessive A/C high side pressure
- The heat load at the A/C condenser
Once engaged, the compressor clutch will be disengaged for the following conditions:
- The ambient air temperature is less than 4°C (40°F)
- The throttle position (TP) is 100 percent
- The A/C low pressure switch is open
- The A/C high side pressure is more than 2957 kPa (429 psi)
- The A/C low side pressure is less than 151 kPa (22 psi)
- The engine coolant temperature (ECT) is more than 121°C (250°F)
- The engine speed is more than 5,500 rpm
- The transmission shift
- The PCM detects excessive torque load
- The PCM detects insufficient idle quality
- The PCM detects a hard launch condition

AUTOMATIC OPERATION
In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature Actuators, the mode actuator and the recirculation actuator.
To place the HVAC system in Automatic mode, the following is required:
- The Auto switch must be activated
- The air temperature switch must be in any offer position offer than full hot or full cold position
Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature:
- Monitors the following sensors:
- The inside air temperature sensor
- The ambient air temperature sensor
- The lower left air temperature sensor
- The lower right air temperature sensor
- The upper left air temperature sensor
- The upper right air temperature sensor
- Regulates blower motor speed
- Positions the air temperature actuators
- Positions the mode actuator
- Positions the recirculation actuator
- Requests the A/C operation

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 an very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.
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 to the refrigerant. The refrigerant is discharged from the compressor, through the discharge hose, and forced to flow to the condenser and then through the balance of the A/C system. The A/C system is mechanically protected with the use of a high pressure relief valve. If the A/C refrigerant pressure sensor were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system. Compressed refrigerant enters the condenser in a high temperature, high pressure vapor state. As the refrigerant flows through the condenser, the heat of the refrigerant is transferred to the ambient air passing through the condenser. Cooling the refrigerant 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 tins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line, to the orifice tube. The orifice tube is located in the liquid line between the condenser and the evaporator. The orifice tube is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the orifice tube, the pressure on the refrigerant is lowered. Due to the pressure differential on the liquid refrigerant, the refrigerant will begin to vaporize at the orifice tube. The orifice tube also meters the amount of liquid refrigerant that can flow into the evaporator.
Refrigerant exiting the orifice tube 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 boil inside of 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 back to the compressor, in a vapor state, and 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 will also change form, or condense, and is discharged from the HVAC module as water.

[toynumber2h2]

I have an 03 duce that had a inop A/c system when I bought it. All new componets and my A/C blowes 40 deg while driving, it does warm up 3-5 deg while sitting in traffic but cools back down when I start rolling..

[jsbihn]

Yeah, but mine actually does that as I drive.
cold air, then a minute or two later it warms up a few degrees, then it go back down to cold air again

Just trying to figure what exactly is going on