A/C Issue
#1
05-27-2018, 07:19 PM
A/C Issue
First posting so go easy on me.
OK, it's a '98 Sonoma but think close enough for practical purpose.
Bought it last fall, A/C doesn't work, seller said it needs a charge. The engine is the 2.2L with a manual transmission. Turn the A/C to on and the engine does go to a high idle but the compressor clutch does not come on. Relay is good (swapped it with the horn relay and proven to work). Jumper out the relay to engage the compressor clutch and A/C gauges show reasonable pressures on both high and low side and within a short time, got nice cold air blowing out of the dash vent.
Suspect that it might be the pressure switch or the ECM. Switch has 3 wires going to it, black, gray and red w/black stripe. Any way to test that switch or bypass it to test things?
Thoughts, advice?
Thanks
OK, it's a '98 Sonoma but think close enough for practical purpose.
Bought it last fall, A/C doesn't work, seller said it needs a charge. The engine is the 2.2L with a manual transmission. Turn the A/C to on and the engine does go to a high idle but the compressor clutch does not come on. Relay is good (swapped it with the horn relay and proven to work). Jumper out the relay to engage the compressor clutch and A/C gauges show reasonable pressures on both high and low side and within a short time, got nice cold air blowing out of the dash vent.
Suspect that it might be the pressure switch or the ECM. Switch has 3 wires going to it, black, gray and red w/black stripe. Any way to test that switch or bypass it to test things?
Thoughts, advice?
Thanks
#6
06-01-2018, 11:40 AM
I believe that the OP states proper gauge pressures and vent cooling when he hot wires the compressor. This appears to be a sensor, wiring or electronics problem. If someone has a proper wiring diagram for his vehicle I will try to help. The Blazer diagram for that year has different wiring colors than he has on his truck.
George
George
#7
06-02-2018, 08:22 AM
I believe that the OP states proper gauge pressures and vent cooling when he hot wires the compressor. This appears to be a sensor, wiring or electronics problem. If someone has a proper wiring diagram for his vehicle I will try to help. The Blazer diagram for that year has different wiring colors than he has on his truck.
George
George
The only wiring diagram I can find shows the PCM. I can see the pressure switch (with 3 wires) and (2) more going elsewhere that mention A/C. Going to make some assumptions here.
1. Because if I jumper the relay controlling the compressor clutch, compressor runs, low side pressure is 32 psi and high side is 120 and it wil then blow clod air out of the dasj vent. Pretty safe to assume the compressor is good and it has the proper charge.
2. When the dash switch is turned to the A/C position, the engine goes to high idle so assume that the PCM is getting the request for air and idling up.
3. Assuming that the pressure switch is working or it would not go to high idle.
Don't think it would be a good idea to jumper inputs or out puts on the PCM. If now in working order, very well might not after that.
If I knew what the 2 other wires from the PCM are supposed to do, if input or output, ground or hot and if hot, 5 or 12v. That would go a long ways to solving this mystery.
#8
06-02-2018, 09:30 AM
Found a 98 four cylinder diagram which looks like what you are describing.
The pressure sensor is a three wire affair. The PCM supplies a 5v reference On the gray wire. What's your voltage on this reference wire?
The sensor is grounded through the black wire through the PCM. Is this ground OK?
The red/black wire is the sensor output to the PCM. Here is a three wire test procedure:
When you pull the AC relay, do you have 12v power at the pin 3 lug in the relay box which is fused power for the compressor clutch which gets routed through the relay when it is energized.
Are you getting fused 12 v power at the input to the relay coil on pin/lug 2? The way the system works is that a call for cooling grounds the other side of the relay coil through the PCM which energizes the relay coil which has fused hot on the other side of the coil. This closes the contacts which takes fused hot from pin 3 and sends it to the compressor on pin 5.
Report back and we'll go from there.
George
The pressure sensor is a three wire affair. The PCM supplies a 5v reference On the gray wire. What's your voltage on this reference wire?
The sensor is grounded through the black wire through the PCM. Is this ground OK?
The red/black wire is the sensor output to the PCM. Here is a three wire test procedure:
When you pull the AC relay, do you have 12v power at the pin 3 lug in the relay box which is fused power for the compressor clutch which gets routed through the relay when it is energized.
Are you getting fused 12 v power at the input to the relay coil on pin/lug 2? The way the system works is that a call for cooling grounds the other side of the relay coil through the PCM which energizes the relay coil which has fused hot on the other side of the coil. This closes the contacts which takes fused hot from pin 3 and sends it to the compressor on pin 5.
Report back and we'll go from there.
George
#10
06-02-2018, 06:56 PM
Found a 98 four cylinder diagram which looks like what you are describing.
The pressure sensor is a three wire affair. The PCM supplies a 5v reference On the gray wire. What's your voltage on this reference wire?
4.85 Volts
The sensor is grounded through the black wire through the PCM. Is this ground OK?
If I check continuity to ground, no, shows 4 mega ohms to ground, not sure this is how to check the ground
The red/black wire is the sensor output to the PCM. Here is a three wire test procedure:
Will check this tomorrow.
https://m.youtube.com/watch?v=JXWqWt1qotg
When you pull the AC relay, do you have 12v power at the pin 3 lug in the relay box which is fused power for the compressor clutch which gets routed through the relay when it is energized.
Yes
Are you getting fused 12 v power at the input to the relay coil on pin/lug 2? The way the system works is that a call for cooling grounds the other side of the relay coil through the PCM which energizes the relay coil which has fused hot on the other side of the coil. This closes the contacts which takes fused hot from pin 3 and sends it to the compressor on pin 5.
Yes
Report back and we'll go from there.
George
The pressure sensor is a three wire affair. The PCM supplies a 5v reference On the gray wire. What's your voltage on this reference wire?
4.85 Volts
The sensor is grounded through the black wire through the PCM. Is this ground OK?
If I check continuity to ground, no, shows 4 mega ohms to ground, not sure this is how to check the ground
The red/black wire is the sensor output to the PCM. Here is a three wire test procedure:
Will check this tomorrow.
https://m.youtube.com/watch?v=JXWqWt1qotg
When you pull the AC relay, do you have 12v power at the pin 3 lug in the relay box which is fused power for the compressor clutch which gets routed through the relay when it is energized.
Yes
Are you getting fused 12 v power at the input to the relay coil on pin/lug 2? The way the system works is that a call for cooling grounds the other side of the relay coil through the PCM which energizes the relay coil which has fused hot on the other side of the coil. This closes the contacts which takes fused hot from pin 3 and sends it to the compressor on pin 5.
Yes
Report back and we'll go from there.
George