Automotive Air Conditioning Information Forum (Archives)

Provided by

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

ac request pin 62

monty101 on Wed October 22, 2014 1:36 PM User is offlineView users profile

Year: 97
Make: buick
Model: lesabre
Engine Size: 3.8
Country of Origin: United States

I need to know what electrical signal the PCM gets from the climate control controller
at PCM pin 62 so the PCM will command the ac clutch will come on if the AC pressure sensor indicate it is permitted?

Is a 5 volt signal or 12 volts or what?

AC_Doc on Sun October 26, 2014 10:48 AM User is offline

According to my reference,
PCM pins 62-63 are the Low and High side connections of the AutoTransaxle Input Shaft Speed 2-wire magnetic sensor.

Sometimes you must accept things at faith value!

monty101 on Sun October 26, 2014 1:02 PM User is offlineView users profile

here is the link I am going by:

It shows that the 62 pin on
a 1997 3800 is:

1997 3800 Series 2 OBD2 PCM wiring instructions fo
Pin Wire Color Circuit Description Action Pin Additional

62 dk grn/wht A/C Request

If I am wrong can you tell me which pin is the pin that receives the "clutch request" signal from the
ac controller on a climate control 1997 lesabre? I also need to know what electronic signal is received
by the pin. I was told it is just 12 volts. I need the ac to come on and the car no longer gets the
proper signal. Pls also tell what color the wire is too.

mk378 on Sun October 26, 2014 7:38 PM User is offline

These are usually "negative logic" circuits, voltage (5V or sometimes 12V) means the function is INactive, the control head pulls the wire to ground to activate A/C.

Your PCM may have a compressor lockout function, if the compressor starts short-cycling due to low refrigerant, the PCM blocks it until the code is reset. On that era of car, disconnecting the battery will reset it.

AC_Doc on Sun October 26, 2014 10:28 PM User is offline

Interesting! PCM Pin C1 62 shows up in two places.

You didn't mention if you have manual or automatic climate control head.

THe repair manual ALSO shows a PCM C1 pin 62 AC Request Input .8 LT GRN. The manual dash selector switch in positions MAX, AC BI-LEVEL, DEFOG, and LOWER supplies PCM pin 62 with a 12V control signal. The 12V input is from "IP FUSE BLOCK" HOT IN RUN, BASE A/C FUSE 50, 25A on 1 BRN 41 to the selector switch and leaves the selector switch on .8 LT GRN to PCM Pin 62.

THe electronic heater A/C programmer controller gets its 12V power from MISC/RDO/CLSTR FUSE 9C 10A through a .5 ORN 40 to the automatic control and leaves on e a .8 DK GRN/WHT 762 wire to PCM Pin 62.

Good luck!

Sometimes you must accept things at faith value!

monty101 on Tue October 28, 2014 4:24 PM User is offlineView users profile

My Lesabre has climate control. I'm kinda confused about the posting.

If I am reading the first reply right? It says pin 62 when grounded will turn on the compressor. Am I reading this right?

Then in the 2nd post it says that when pin 62 receives 12 volts it turns on the compressor.

In the second post it appears the info came out of a repair manual. It appears

the first post is just a general statement about how these requests are usually activated and it appears

usually it is activated when grounded. If so it does not not specifically refer to the Lesabre and I should

consider the 2nd request as the ans that will work with the 97 Lesabre. Am I correct about this?

Edited: Tue October 28, 2014 at 4:39 PM by monty101

AC_Doc on Tue October 28, 2014 4:40 PM User is offline

mk378 mentions "negative logic" for the OUTPUTS of the PCM which is correct. Its MUCH easier for the PCM to GROUND a signal than it is for the PCM to source voltage to make something happen.

For theINPUTS to the PCM they could be 5V or 12V. All newer model cars have replaced PCM 12V logic with 5V logic. Your 1997 still uses 12V signals to the PCM. When you turn on the A/C from the positions on the knob or the climate controller signals the PCM the signal to PCM pin62 is +12V to energize the compressor clutch (provide all the other monitoring sensors are correct). The lack of any voltage on PCM Pin62 tells the PCM no A/C request exists.


Sometimes you must accept things at faith value!

monty101 on Fri October 31, 2014 7:51 PM User is offlineView users profile

Been looking at the PCM on this 1997 Lesabre. It has two wiring harness connectors. Which one has the AC Rquest Pin?
I think they are C! and C2 but they aren't labeled. but the pin numbers are idetified on the PCM itself. I am of the opinion
that pin 62 is the correct one. Am I correct about that? Which of the two connectors has the pin 62 I am looking for?
Thanks. I intend to test it by hooking a hot wire up to it that has 12 volts to make sure that it will get the compressor to
come on.

AC_Doc on Sat November 01, 2014 5:20 PM User is offline

I checked another source! Found this which might help you.

The schematics do show two connectors C1 and C2.
A note that Connector C1=80 pin BLU, C2=80 CLEAR

On the A/C schematic page:
The PCM C1 pin62 A/C request input wire color is Lt. Green.

Also, the PCM C1 Pin35 is an output Dk. Grn/Wht wire to the Compressor Relay coil pin 85. Puts Ground on this wire to energize the Compressor Relay and apply power the compressor clutch coil.

The other side of this Compressor Relay coil pin 86 wire pink goes to a +12V Instrument Panel Fuse called "Non OBDII Misc Eng Fuse 7E 10A"

Do you have a website ot throw-away email address contact??


Sometimes you must accept things at faith value!

Edited: Sat November 01, 2014 at 5:29 PM by AC_Doc

GM Tech on Sat November 01, 2014 7:37 PM User is offline

No "lock-out" on this vehicle- the compressor does not "short cycle" it doesn't cycle at all- it is a variable stroke v-5 system- no cycling switch.

I would be sure the ECM is or is not doing its job-- does your inputs to ECM look okay- as in pressure transducer reading above 47 psi-- if you have Auto temp control, is outside temp reading above 40 degf?

I have seen one in my life, that would not give out a neg output to the relay- ended up wiring a low pressure switch to the input leg of relay- to make it like a pre- 1994 model- where they used switches instead of transducers-- worked well. just no cut-out on wide open throttle, or high pressure cut-out- could have wired a HPCO switch though.

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

monty101 on Sun November 02, 2014 5:08 PM User is offlineView users profile

My email address is :

Thanks again

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.