99 astro a/c help

[toddluck69]

took my van to the shop cause it wasnt blowing cold..i recharged the system and still nothing ..so i was forced to take it in ...they ran all there checks on it and could find any component not working so they said they thought it was computer related??....do these vans a seperat computer for the a/c or is it all wrapped up in the main computer

[toddluck69]

bump

[old_master]

The A/C compressor clutch is not controlled by the ECM. There is a circuit that goes to the ECM so it can adjust the idle speed when the clutch is engaged, but that's the only thing the ECM does as far as the A/C goes. There are however, a series of switches that can prevent the clutch from engaging. First is the dash control switch. Second is the clutch cycling switch, located in the accumulator. Third, the superheat switch located on the rear of the compressor. All three must be functioning properly, along with the associated wiring, fuses and grounds.

You mentioned in your post that you recharged the A/C: It is impossible to fully charge the system if the clutch does not engage which may be why the system is not cooling. Before you charged the system, did you drain the system? Did you evacuate the system? Did you check the oil in the system? Did you add PAG oil? Did you install the proper amount of R134a refrigerant? Did the clutch cycle during and after the charge? If the clutch was cycling after it was charged, what were the high and low side pressure readings at clutch cut in and cut out? To diagnose any problem, you need to understand how a system is supposed to operate, then gather the necessary data to make a diagnosis. I need more data.

[boatbuster]

Old Master stated the use of PAG oil, I was about to refill my a/c system myself but was a little concerned that the sticker on my a/c says to use R134A with synthetic oil, is that the same thing as PAG oil??? Thanks!

[toddluck69]

new dash panel switches new resitor pack
checked the switch on the accumulator and the shop said it was working??
all fuses are good
is there a way i could test the cluch and the super heat switch

Originally Posted by old_master

The A/C compressor clutch is not controlled by the ECM. There is a circuit that goes to the ECM so it can adjust the idle speed when the clutch is engaged, but that's the only thing the ECM does as far as the A/C goes. There are however, a series of switches that can prevent the clutch from engaging. First is the dash control switch. Second is the clutch cycling switch, located in the accumulator. Third, the superheat switch located on the rear of the compressor. All three must be functioning properly, along with the associated wiring, fuses and grounds.

You mentioned in your post that you recharged the A/C: It is impossible to fully charge the system if the clutch does not engage which may be why the system is not cooling. Before you charged the system, did you drain the system? Did you evacuate the system? Did you check the oil in the system? Did you add PAG oil? Did you install the proper amount of R134a refrigerant? Did the clutch cycle during and after the charge? If the clutch was cycling after it was charged, what were the high and low side pressure readings at clutch cut in and cut out? To diagnose any problem, you need to understand how a system is supposed to operate, then gather the necessary data to make a diagnosis. I need more data.

[brcidd]

the switch in the back of the compressor is actually a high pressure cut-out switch which is normally closed and opens at 425 psi- then closes at about 250 psii-- you can temporarily jumper the wiring connector to test if switch is stuck open.

[old_master]

Originally Posted by boatbuster

Old Master stated the use of PAG oil, I was about to refill my a/c system myself but was a little concerned that the sticker on my a/c says to use R134A with synthetic oil, is that the same thing as PAG oil??? Thanks!

PAG oil, (Polyalkaline Glycol), is a synthetic and must be used where specified. DO NOT mix Ester or mineral oil with it.

[old_master]

Originally Posted by toddluck69

new dash panel switches new resitor pack
checked the switch on the accumulator and the shop said it was working??
all fuses are good
is there a way i could test the cluch and the super heat switch

As Brcidd mentioned, the superheat switch is normally closed. If the refrigerant is superheated, (pressure reaches approx. 450psi), the switch will open an interrupt current flow to the clutch field. Unplug and jumper the terminals in the connector to test the switch. To test the clutch and field, unplug the connector at the field. Ground one terminal on the field and apply battery voltage to the other.

[toddluck69]

so when i test the conecter will it click??...or do i have to have the a/c on

[old_master]

I checked the factory shop manual, and some of the information I supplied earlier is incorrect. Sorry for the confusion. Here is the correct information.

The VCM does control the clutch field. The “A/C request” circuit comes from the mode switch, through the superheat switch to the VCM. The clutch cycling switch, (located on the accumulator), senses low side refrigerant pressure. If the switch senses refrigerant pressure is above approximately 42psi, the VCM will energize the clutch relay. The relay then energizes the field, the clutch engages and the compressor runs. As the compressor runs, low side pressure drops. When the low side pressure drops to approximately 22psi, the clutch cycling switch opens, the VCM shuts off the clutch relay, the clutch disengages, and the compressor stops. When the low side pressure rises to 42psi the cycle starts over.

To test the superheat switch, (located on the rear of the compressor): Unplug the connector and check the resistance between the two terminals of the superheat switch, (very limited room to access the switch). Resistance should be less than 5 ohms. The light blue wire comes from the mode switch. The dark green with a white stripe wire goes to the VCM.

To test the clutch and field: Unplug the connector at the field, ground one terminal of the field and apply battery voltage to the other. You should see and hear the clutch engage. The dark green wire comes from the relay. The black wire goes to ground.

To check the clutch cycling switch: Unplug the connector and check the resistance between the terminals on the field. Resistance should be less than 5 ohms IF there is more than 42psi in the system. Resistance will be infinite, (open circuit), if the refrigerant charge is below 42psi. The dark green wire goes to the VCM. The black with a white stripe wire goes to ground.

[vettepin]

i have the same problem the frt ac is warm ,but when i turn on the rear a/c the frt gets cold again . so think its the frt evaporator core, or a orfice clogged ,maybe???