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Gary, Chevy Technician
Category: Chevy
Satisfied Customers: 17138
Experience:  15 years GM master tech
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My ac is not working on my 2001 chevy s10 2.2 need ecu

Customer Question

my ac is not working on my 2001 chevy s10 2.2 need ecu pinout diagram and some starter diagnostics to run
heres what i know:
1: if i jump the clutch relay with a paperclip it runs fine
2: when i turn the switch inside to an a/c on setting i get an idle change
Submitted: 2 years ago.
Category: Chevy
Expert:  Roy replied 2 years ago.

good morning my name is ***** ***** I will assist

I attached a wiring diagram of the ac system for you to view. the pcm will ground the relay to activate depending on inputs from the high pressure and low pressure switches. check the voltages at each first and make sure you have both powers at the relay.


Customer: replied 2 years ago.
there is only one sensor......
its on a thin pressure line on the left side of the engine bay its a 3 wire sensor
the diagram says there is one on the back of the compressor.
there is only one electrical connection to the compressor and that is for the clutch activation
so..... not sure what to do here
Customer: replied 2 years ago.
pretty sure thats the wrong diagram since my sensor has three wires and those only have two for the sensors
Expert:  Roy replied 2 years ago.

that is the only listing for the diagram that I have.

is there a switch on the dryer???


Customer: replied 2 years ago.
no other visible sensors on any pressure lines or accumulator or even wires coming out of any component in the system.........
Expert:  Roy replied 2 years ago.

ok, I will opt out for someone else that may have a better or other diagram for you

sorry I could not be more help


Customer: replied 2 years ago.
thanks anyway for trying
Expert:  Gary replied 2 years ago.

new expert here are these the 3 wires for the pressure sensor wiring diagram you need ?

there should only be 1 - 3 wire ac switch/sensor for this system

Customer: replied 2 years ago.
yeap i got reference 5 volts and ground continuity
need to check for output signal
i replaced this sensor maybe a month ago thinking this might be the problemwhere do i check on the pcm to see if it is receiving the signals from the a/c switch and the sensor?is this attached the correct diagram for my ecu???? and if it is how can i tell which connector is 1 and which is 2?
Expert:  Gary replied 2 years ago.

one ECM connector is blue colored and the other is black colored

you want connector C1 terminal # ***** the wire color is red/black

and you want the BLUE colored ECM connector

Customer: replied 2 years ago.
its 35 for the a/c request signal correct
and 49 is the output from the sensor?
Expert:  Gary replied 2 years ago.

49 is the output from the sensor to the computer on the blue connector

36 is the AC request signal

Customer: replied 2 years ago.
ok i get 12 volts to the computer on 36 lt blu
i get 1 volt from the sensor on 49 red/blk? is that right?also i checked the relay in the fuse box by swapping it out with a known good relay from the horn which uses the exact same relayi checked the terminals for the relay and it gave me some confusing readingsthe front two terminals read 12 volts when turned to max a/c back two read 0(front means towards front of the truck)
the front two terminals read the same 12 volts when a/c is turned to off
the REAR two terminals read 12 volts when the fan is on vent with the a/c turned off
Customer: replied 2 years ago.
is the sensor supposed to output a signal when the a/c compressor is off?
it only reads 1 volt when i jump the terminals for the a/c relay to turn on the compressor
it reads zero when the compressor is not running
Expert:  Gary replied 2 years ago.

yes when it is off it will still send a signal back as there is pressure in that ac system which i hope is filled to exact R134 spec amount of R134

Customer: replied 2 years ago.
maybe i have the wrong sensor?
it sends out 0 volts when the compressor is not running and only 1 volt when it is
as for the charge i know it has 45 -48 psi low side when compressor is running
and about 120 psi on the low sidewhen compressor is not running
i can only test low side right now as i dont have access to a proper set of auto gauges
just a low side pressure gauge(not one of those things that go on the can its a standalone gauge)
i might be able to go borrow a set though if thats not enough information
Expert:  Gary replied 2 years ago.

either the sensor is wrong or the red/black wire from the ac switch to the computer is bad the system is not charged correctly or the computer is bad

as long as on the ECM connector C2 terminal # ***** a dark green /white wire does NOT show a ground when the ac is turned on with the engine running

Customer: replied 2 years ago.
the red/black wire at the ecu shows the same voltage of zero when compressor is not running and 1 volt when it is running so the wiring is good
going to go try to borrow some gauges
and check for that ground
Expert:  Gary replied 2 years ago.

ok the ground that is supposed to turn on and off on terminal 55 is when the computer wants to turn on the ac and that wire is the ground for the ac relay to turn on the relay if no ground when the trucks on and ac on then our issue is not the correct R134 in the system or a bad switch or the computer is bad

you have the ac request and the 5 volts and ground at the switch

kind of narrows this issue right down to those things i said being the problem

Customer: replied 2 years ago.
I borrowed a set of automotive gauges and the refrigerant charge is fine. How many volts is that sensor supposed to put out?
Expert:  Gary replied 2 years ago.

it should show 1.5 to maybe 2 volts

if you unplug it will the ac turn on if not if you jump the 5 volts to the signal wire at the connector will it turn on ?

Expert:  Gary replied 2 years ago.

how are you making out ?

dont forget to rate us here at Justanswer !

Customer: replied 2 years ago.
sorry been busy with work
but i just got on it today
i dont see ground continuity(constant beep tone from dvom) at the terminal in the fuse box where i should see the pcm ground if i go from a battery ground or a body ground
but if i go from positive battery terminal to that same terminal( pcm activated ground) i get 12 volts........ so im getting a complete circuit i think
i get 12 volts with the pressure sensor plugged in and when i jumper the 5 volt reference to the sensor output
Expert:  Gary replied 2 years ago.

at this point i think we need to see if we can get a second opinion

hang on another expert will rely back to you