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Still looking idea on WOT relay. Cuts power to A/C compressor, controlled by PCM

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  • Lincoln Master
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Wide open throttle signal goes to PCM from the TPS, throttle position sensor. mounted on throtle body

Throttle Position Sensor The throttle position (TP) sensor (Figure 39) is a rotary potentiometer or Hall-effect sensor that provides a signal to the PCM that is linearly proportional to the throttle plate/shaft position. The sensor housing has a three-blade electrical connector that may be gold plated. The gold plating increases corrosion resistance on terminals and increases connector durability. The TP sensor is mounted on the throttle body. As the TP sensor is rotated by the throttle shaft, four operating conditions are determined by the PCM from the TP. Those conditions are closed throttle (includes idle or deceleration), part throttle (includes cruise or moderate acceleration), wide open throttle (includes maximum acceleration or de-choke on crank), and throttle angle rate.

Posted on Jul 02, 2009


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SOURCE: WOT cutout relay, always on, A/C compressor wont engage

replace th relay, this is a common problem

Posted on Jun 29, 2009

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Does a 2004 jeep grand cherokee have and fuel cut off switch?

No shutoff switch they will have an electric relay.

Dec 15, 2016 | Jeep Cars & Trucks

1 Answer

Compressor clutch engages when I jump the relay, and I already bought a new relay. What could be preventing the compressor from recording power.

The compressor from recording power ? First off what make , model an year vehicle ? When you jump the pins where the relay plugs into , By the way that should be pin's 30 & 87 .look on the bottom of the relay .Besides 30 & 87 you will also see pin's 85 & 86 ! 85 ,86 are the control side . When you push the A/C button on the control head ,depending on make , model an year vehicle , the control head sends a turn on request to the BCM - body control module or right to the PCM - engine computer .The PCM will then energize the compressor clutch relay ! Is there control from PCM ? Before the the relay will be energized the PCM looks for a signal from high an low pressure cut out switches . Your best bet would be to take your vehicle to a qualified repair shop .

Aug 05, 2016 | Cars & Trucks

1 Answer

Where is the AC fuse on a 2005 Ford escape located

A/C fuse ? Compressor clutch not coming on ? HVAC control panel ? When you push that A/C button ,that is an input to the PCM - engine computer . The PCM then energizes the A/C clutch relay turning on the compressor clutch . The odds of this being a fuse problem is astronomical . But check fuse F14 15amp in under hood fuse box . Check A/C clutch relay also ! Check power an control of relay ,do you know what this is ? Go on you tube an check out video on test a relay .

Apr 03, 2016 | Ford Cars & Trucks

1 Answer

Why my Suzuki sx4 ac compressor not working?

manual A/C system or the fully auto system? option?

lots and lots of reasons, i can list them all , im the electric guy.
08 SX4 , (USA spec car)
answer 1: get it serviced? not an options? do say? we cant guess
what your question is, why, ? see #1 below for users DIY.
so is the compressor dead , on engine.

  1. a/c fuses blown to any A/C device, includes blower, in heater.
  2. A/C relays bad.
  3. High/low pressure switch tripped open (loop issues (Freon(tm)
  4. AC amp (logic box) sees errors, on any of 6 inputs.
  5. they all worked before, all cars, but not now for cause.
now the step 4 elaborations..
the AMP cuts the compressor fan and clutch for many reasons,
most not for your cause. but is important all.
why,. because those wires there can fail, or even fall off.
on the 2008 the AMP is now BCM/PCM/HVAC control module
the first step is after fuse checking is the do a full OBD2 one
SCAN on the PCM port. see if there are DTC errors. (do that now)
logic fails. BCM controls the front fan (cond) or PCM does on manual AC option.
  • blower voltage dead. (Blow logic failed)
  • engine overheated (or sensor lies) "wires fell off?"
  • engine overloaded, a/c cuts at crank, and wide open throttle.
  • hi/lo switch cuts out, protecting loop from DAMAGE.
  • lots of sensors can fail here, scan it?
  • outside air temp, too cold to run A/C? (auto system)
  • evap core icing up sensor, shows too cold, near 32f.
  • The manual system uses PCM to operated the 2 main AC relays as a slave to the AC brain box. but is BCM on fancy auto system.
  • not scanning the PCM/BCM now, you will FAIL.
The manual system is below. seen in the FSM book.
the tests are easy do you want me to gue$$ or TEST.


Feb 28, 2015 | 2008 Suzuki SX4

1 Answer

Wiring diagram

are the A/C fuses good? what transmission, auto or stick?
the first check is , does the compressor, cultch, engage
and spin the actual compressor main shaft at full speed.
yes, then loop is bad. (freon loop) (fan good)
No, then below is wrong. (electrical)
did you check pressures yet?
if not , then the hi/low limit switch may be open killing the compressor
so it dont self destruct, never bypass this limit switch.
the High low switch if open kills DC power to the A/C main relay. coil.
coil yellow wire must be at 12vdc or the loop has wrong pressures.!
dig,. it refuses to destroy its self. so kills the relay.

all posts, USA.
does the A/C lamp on dash turn on? if not the blower is dead.!
on the 94,(i dont have 93 drawings)
you can get better drawings for 94 at, any time.
yellow wire is hot. (clutch dead)

the next point of failure is the car has throttle pedal switch
that is closed all time but wot, wide open throttle cuts AC.
so this switch can fail and cut A/c (USE A VOLTMETER) opens.
the clutch has its own relay, that is controlled by
the A/C amp module (better name A/C logic module)
it cuts A/C for many reasons.
we use a voltmeter at the AMP mod..

inputs that can stop A/C compressor, are:
1: engine overheat sensor bad. 0v , goes to 12v at 235F engine temp.
pin 9.
2: pin11, not 12v means dash lamp out
3: pin 5, transmission cut, or throttle pedal cut out (WOT).
4: pin 4 and 10 , evap core iced up cut, thermister sensor.
5: pin 8, lost 12vdc power.

The TCM cut out , to pin 5 is just for automatic trans, with TCM shifter electronics, it sends cut when the trans detects overload.
(hills? or tranny goes to limphome mode, {sick})
see amp below.
that is it, for electrics. answer my first questions for better answers.


Mar 31, 2014 | 1994 Geo Metro

1 Answer

The a/c compressor clutch will not engage even when I jump the low pressure switch thats mounted on the top of the accumulator (dryer). Is there another method such as direct from the battery? There are...

The low pressure switch is just a sense input to the PCM - powertrain control module > Grantit , it is needed for the PCM to know the pressure in the system . But the PCM must energize the compressor clutch relay for the compressor to engage . Finding the compressor clutch relay in the under hood fuse / relay box an testing there would be the best place to start . Pull the relay out of the fuse box , look on the bottom ! You should see four set's of number's ,30 & 87 plus 85 & 86 . 30 & 86 should have B+ voltage . Use a multi-meter to test . 85 goes to pin # 1 connector 3 at the PCM . The PCM supply's a ground here to energize the relay if condition's are right . You could jump pin's 30 & 87 an if the compressor clutch coil is good ,the compressor clutch will engage . Video's on youtube showing how to do these test .

Dec 12, 2017 | 2002 Jeep Liberty

2 Answers

I have a 2002 buick lesebre and the ac is not working.. on the back of the pump there is a plug going to the tube and then the tube runs to the ac pump so I pulled that plug and it has power going to it....

{: ) The a/c blower controls is independent of the a/c compressor system. Meaning, the blower can still deliver air even if your compressor system is not working or not cooling.
I assume your blower functions are okay, since you are now focused on probing power to all those connectors near the compressor.
If I imagine it right, the first plug you pulled has three wires on it and it should be the a/c refrigerant pressure sensor. The next plug you said where the a/c clutch is, has two wires on it, and obviously that's the a/c clutch/compressor connector. Just for safety reminders, never apply direct 12v power to any of those plugs that you pulled, especially the pressure sensor, because you may damage the PCM and other components and will only worsen the problem. I'll show you a sample diagram of the compressor controls just to give you an idea. A/C Controls 101:
The red lines indicate the flow of 12v power once the relay is energized. Power from the battery flows thru the A/C CLU fuse at the underhood fuseblock (you can check this fuse if busted) and then flows thru the a/c relay (you may also substitute a similar relay for testing) going to the compressor. This continuos flow happens only when the relay is activated.
The green line indicates the request signal coming from the PCM to energize the relay. The PCM monitors several inputs like the pressure sensor inputs, the a/c control switch on the dashboard, the engine temp, and others. Based on gathered inputs it will decide when to give a request signal to energize the relay that will activate the compressor.
So you see, if one of the inputs do not agree, or if there is a fault on the engine sensors, the a/c controller, or the PCM itself, no 12v power will be present on the a/c clutch connector.
The fuse, relay, and clutch can be easily tested with basic tools like the test light or multimeter. But if the fault comes from the control signals, you will need a more comprehensive diagnostic approach. A scan tool is very effective in diagnosing signal faults.
You may need to check also the refrigerant charge. So goodluck.

Jul 24, 2011 | 1994 Buick LeSabre

3 Answers

Put in a new dash control panel,new pressure switch,full of freon.fuses and relays are good. jumped low pressure switch.still no power to ac clutch. HELP..

YOUR a/c compressor is cut on by the vehicle pcm(computer).pcm sends a signal to a/c relay to energize relay which sends power to compressor. Have you checke dall the fuses with a test light? last dodge i worked on had a blown horn fuse which powered a/c system also. block said nothing about this. here is a diagram999f7d5.gif

May 21, 2010 | 2003 Jeep Liberty

1 Answer

A/C compressor turns on and off even though A/C is switched off

Hello akaobaer...Sounds like you have a pressure switch defective or the system charge (freon) is low...The a/c clutch relay is operated by the Powertrain Control Module. However there are inputs from the low pressure switch (located on the accumulator) and a high pressure cut out switch (located on the discharge line near the compressor) that control whether or not the PCM turns on the clutch relay as well.
If the refrigerant level is low, the PCM low PSI switch will cause the clutch to cycle.
The PCM turns on the relay by grounding the negative side of the relay coil...The low PSI switch should turn on (close) at approx 34 PSI.....and will turn off (open) at 20-22 PSI...May sound complicated but it's really not. Have a qualified HVAC tech. check the system for leaks before recharging it, if needed.
Good luck...i hope this answers your question and will fixya up...

May 19, 2009 | 1999 Jeep Grand Cherokee

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