Technical Turning on A/C cuts engine at idle

[tonyb0902]

Immediately after Dealer fitted new thermostat & housing, the engine cuts out at idle as soon as A/C is turned on. Cleaned throttle body - no change.
Fitted new Idle Speed Control Valve/Stepper Motor - no change.
Carried out learning procedure - no change.
Engine runs fine otherwise.
About to clean throttle body again but this time taking it off manifold so as to access the engine side of throttle plate.
Any ideas?

 

[the green vanper]

Hello,

It'd be interesting to see the errors.

On higher revs does the A/C switches on normally?

 

[koalar]

Is it just the the AC that causes a problem

If you say wind the windows up and down or put the rear heated window on and off a few times

It's easy to mess up the throttle body by flooding it with carb cleaner as per many videos on YouTube, if it gets onto the position sensor they will fail days,weeks,,months or years down the line

On your scantool what are the idle actuator steps

 

[tonyb0902]

Hi,
All other applied electrical loads result in the Idle Speed Stepper Motor working correctly, no issues at all. When the A/C is turned on, the engine dies immediately as soon as the A/C Clutch actuates.
The A/C Compressor is free to rotate with no indication of abnormal restriction, no belt squeal/noise etc.
We took car in to have the thermostat changed and all was fine but the technician rang me immediately after fitting the thermostat and reported the issue.
The thermostat had not operated properly for 2-3 years with the engine never reaching operating temperature. Fuel consumption has dropped to around 30 mpg (from 55 mpg). Unfortunately I had been unwell and could not sort it out myself. I wonder if the excess furling had hidden this issue for some time.
All ideas welcome, just going to get an OBD Scanner.

 

[tonyb0902]

Hello,

It'd be interesting to see the errors.

On higher revs does the A/C switches on normally?

Yes, all otherwise is fine.

 

[koalar]

Am I reading this right

Fuel consumption has dropped to around 30 mpg (from 55 mpg).

Since the thermostat has changed you are using nearly twice the fuel

Does it feels sluggish,compared to normal

 

[tonyb0902]

Am I reading this right



Since the thermostat has changed you are using nearly twice the fuel

Does it feels sluggish,compared to normal

No. Before thermostat was changed 30 mpg, since 55 mpg
Runs fine

 

[koalar]

I don't immediately see any connection between the thermostat change and stalling when the Aircon is a activated, but not when any other electrical device is actived

In the scan tool, graph the requested rpm and actual rpm

When the Aircon is activated does the requested rise

Do the actual fall a bit before it cuts out

What is it idling at

Not sure where to start, take a photo with the air box off from the thermostat side, let's see what which lay out of component are on this engine fiat change things slightly around 2009

 

[tonyb0902]

I don't immediately see any connection between the thermostat change and stalling when the Aircon is a activated, but not when any other electrical device is actived

In the scan tool, graph the requested rpm and actual rpm

When the Aircon is activated does the requested rise

Do the actual fall a bit before it cuts out

What is it idling at

Not sure where to start, take a photo with the air box off from the thermostat side, let's see what which lay out of component are on this engine fiat change things slightly around 2009

Hi
Engine idles smoothly at 800 rpm.
The engine controls responds perfectly to all other applied electrical loads - rpm momentary blips upwards then settles back to 800 rpm.
Activate A/C and engine cuts instantly.
A/C Compressor Clutch freely rotates and when actuated only applies minimal added drag.
There could be a reason why changing thermostat caused change - thermostat been defective and deteriorating for three years. The ECU may have tried to accommodate that situation by fueling. When thermostat changed it may be out of acceptable range - just an idea?
Waiting for scan tool - enroute from China!
Best regards

 

[jrkitching]

the Aircon is a activated, but not when any other electrical device is actived

The aircon compressor isn't an electrical load; it's a mechanical one, and a pretty hefty one at that; an instantaneous demand of another 4-5 HP from the engine.

The ECU should automatically adjust the fueling to compensate for this; I'm thinking this additional fueling isn't happening in the way it should be.

You can simulate a similar load by putting the car into first gear, then gently letting out the clutch without touching the accelerator pedal. The car should pull away; if this stalls the engine, the cause will most likely be the same. Something you can try without needing any tools or software.

 

[tonyb0902]

The aircon compressor isn't an electrical load; it's a mechanical one, and a pretty hefty one at that; an instantaneous demand of another 4-5 HP from the engine.

The ECU should automatically adjust the fueling to compensate for this; I'm thinking this additional fueling isn't happening in the way it should be.

You can simulate a similar load by putting the car into first gear, then gently letting out the clutch without touching the accelerator pedal. The car should pull away; if this stalls the engine, the cause will most likely be the same. Something you can try without needing any tools or software.

Hi
I had checked all the electrical load inputs that affect idle speed control and had satisfied myself that they were all operational (engine runs fine with excellent idle speed control at 800 rpm).
The input from the fan/air conditioning on switch may be suspect - ? (the originator of the command to the ECU to step-up fueling/throttle) or indeed if the ECU is actually receiving the command from the switch and it is not responding (broken wire/lack of continuity/error in coding or command?). All guesses at the moment and your help is gratefully received - thanks.
When the technician told me that he had changed the thermostat and had found the A/C causing this issue, I asked if he had disconnected the ECU to gain access to the thermostat housing (that is normal, it is pretty tight for space) but he said he had not touched any wiring connections (must be a pretty agile guy, more so than my 73 years permits! ). I was looking for a logical route to the issue.
My course of action, when I receive Scanner (in Hong Kong Airport currently) is to try and identify if a signal is being received from the switch and if indeed the ECU is sending a command back to the Idle Speed Stepper Motor.
A little frustrating but interesting nonetheless the less.
Simulating load by using the vehicle loading is all fine, no stalling etc.

 

[tonyb0902]

Hi
I had checked all the electrical load inputs that affect idle speed control and had satisfied myself that they were all operational (engine runs fine with excellent idle speed control at 800 rpm).
The input from the fan/air conditioning on switch may be suspect - ? (the originator of the command to the ECU to step-up fueling/throttle) or indeed if the ECU is actually receiving the command from the switch and it is not responding (broken wire/lack of continuity/error in coding or command?). All guesses at the moment and your help is gratefully received - thanks.
When the technician told me that he had changed the thermostat and had found the A/C causing this issue, I asked if he had disconnected the ECU to gain access to the thermostat housing (that is normal, it is pretty tight for space) but he said he had not touched any wiring connections (must be a pretty agile guy, more so than my 73 years permits! ). I was looking for a logical route to the issue.
My course of action, when I receive Scanner (in Hong Kong Airport currently) is to try and identify if a signal is being received from the switch and if indeed the ECU is sending a command back to the Idle Speed Stepper Motor.
A little frustrating but interesting nonetheless the less.
Simulating load by using the vehicle loading is all fine, no stalling etc.

One added comment. If the A/C Compressor is adding excessive load (more than calibrated) I would expect complaint from the belt but there is none - what would you think?

 

[koalar]

Photo as per post 8
Graph expected and actual rpm as per post 8
800rpm is not right if the engine is up to temp
Without feedback it's likely we continue to go round in circles

The reason I asked about other
Electrical loads is the ac compressor should have its own earth from its case to the bulkhead and I was wondering if the earth lead was disturbed when the thermostat was changed, It would appear not, time to move on

Slight confusing as a relearn was preformed but the scanner in HK

 

[Mike1alike]

I'd say it's possible the AC compressor to be seized, stuck. The compressor pulley rotates freely but it usually just rotates on its own. It locks on to compressor shaft only after you activate the clutch. So did you test if the compressor can rotate or only the pulley? A stuck compressor can turn the engine off.
Also, there could be an electrical shortcut on the compressor's clutch. Try taking the auxiliary belt off, that way mechanics does not interfere when you turn AC on as the belt is not connected to the compressor pulley. And turn the AC on. If the engine still cuts off the problem is definitely electric and probably as I've mentioned, a shortcut that probably causes ECU to cut out.

 

[tonyb0902]

One added comment. If the A/C Compressor is adding excessive load (more than calibrated) I would expect complaint from the belt but there is none - what would you think?

I'd say it's possible the AC compressor to be seized, stuck. The compressor pulley rotates freely but it usually just rotates on its own. It locks on to compressor shaft only after you activate the clutch. So did you test if the compressor can rotate or only the pulley? A stuck compressor can turn the engine off.
Also, there could be an electrical shortcut on the compressor's clutch. Try taking the auxiliary belt off, that way mechanics does not interfere when you turn AC on as the belt is not connected to the compressor pulley. And turn the AC on. If the engine still cuts off the problem is definitely electric and probably as I've mentioned, a shortcut that probably causes ECU to cut out.

Hi Mike,
As a newcomer to this forum and indeed this way of investigating issues, I am really impressed and grateful. I have three contributors, all great. Thank you.
You may have seen the “thought train” sofar. I cannot proceed with the electronic analysis which is awaiting the delivery of an OBD2 Scanner (hopefully next week).
In the meantime I have focussed on the hardware, the Compressor and Clutch. The engine cuts out as soon as the Compressor Clutch engages, doubtless due the increased load. There is no belt squeal or harsh noises of engagement at this point. Increasing the rpm after re-starting the engine and increasing throttle results in no added noise as the Clutch “bites” (?). A/C works fine at this point, reducing rpm by lifting foot off throttle just results in the engine dying immediately.
I am still considering that the A/C Compressor is adding excessive load but not enough to cause belt squeal or other symptoms. Your thoughts will be well received.
How do I engage the Compressor Clutch with the engine off (but with ignition on) so as to try the load through the Pulley/Clutch Assembly? So far I have only checked the non energised clutch situation/load. With engine not running but with ignition otherwise in run position the Compressor Clutch does not actuate - is that normal?
Have not yet tried removing drive belt.

 

[The Panda Nut]

I would look in mes and see if it recognizes the car has air con. Proxi alignment and re learn the learned functions first. If the air con is ok check the alternator is turning freely. If notvaxfault here its fuelling or a,wiring issue maybe ecu not understanding the air con is switching on

 

[Mike1alike]

@tonyb0902 by what you are saying, the compressor is not seized, that is good.

With engine not running but with ignition otherwise in run position the Compressor Clutch does not actuate - is that normal?

I don't know, I will try that tomorrow on my Punto and report how it goes.
To test how 'free' the compressor is revolving I'd say you do take the belt down and try revolving it by this screw. It's 10 mm on mine, I'm expecting yours is the same. Put a key on it an revolve it clockwise.


I never tried this before. I will do it tomorrow and will tell how it goes.

By your description sounds like it's something like excessive load and ECU not being able to manage it. It could be electrical resistance from oxidized contacts. First on that line is the main ground cable.

 

[koalar]

Raise the rev to 2000 rpm ISH

Engage the aircon

Does it still cut out or the belt squeal

Has the Aircon actually worked recently

We don't know what we are dealing with, does it have the two ignition coils on the right side of the cylinder head or one block under the air filter, 2009 is right at the cut over period

Is the car flyby wire throttle or cable and so on, I'd be surprised if 1.2 with Aircon at 2009 was cable, you don't say whether it's a 1.1 very rare or a 1.2

One picture would make it so much simpler

 

[tonyb0902]

Raise the rev to 2000 rpm ISH

Engage the aircon

Does it still cut out or the belt squeal

Has the Aircon actually worked recently

We don't know what we are dealing with, does it have the two ignition coils on the right side of the cylinder head or one block under the air filter, 2009 is right at the cut over period

Is the car flyby wire throttle or cable and so on, I'd be surprised if 1.2 with Aircon at 2009 was cable, you don't say whether it's a 1.1 very rare or a 1.2

One picture would make it so much simpler

Hi
To answer your questions in order:
Raising rpm to 2000 (or 1500) - engine does not cut out, no belt squeal or any other sign of the drive belt being in distress.
Air Conditioning is working fine, no issues at all.
Two coils to the right hand side.
Car has throttle cable.
Owned by ourselves since new in 2009.
1200
From the reading I have been doing recently I understand that this was a period of real changes in short periods of time.
The strange coincidence that this issue literally occurred immediately after the Dealer changed the thermostat and housing for me? The technician actually rang me to ask if it was like it before I took car in!
Will take photos and attach

 

[PuntoHowTo]

Thinking this though as logically as I can.

So everything presumably worked ok before the thermostat was changed. AC system wasn't touched and I imagine it would be a really unlucky coincidence that the compressor or AC system developed a fault as a result of the thermostat being changed, given there isn't any interaction between these two systems.

So the car was previously operating with very high fuel consumption, it would be reasonable to conclude then that the car was over fueling and running very inefficiently.

Now there are two ways to regulate the idle on modern cars, an electronic air idle control valve, or more recently an electronic throttle butterfly that is opened and closed to regulate the idle.

As stated, previously everything was working, the car, aircon etc was functioning just with high consumption so it maybe the car was operating with the butterfly open more than is would be normally trying to control fueling with a cold engine.

Weird question perhaps but is the cutting out issue better or worse when the engine is hot/cold. Ie when its cold is it more likely to cut out, when its warm or is it about the same? Just something to think about.

When the car engine is cold, it operates in "open loop" the oxygen sensor needs to be warm to function therefore until it has warmed up idle is usually maintained higher until the oxygen sensor is warm and it can switch to operating in "closed loop" when the oxygen readings dictate the fueling. If the car is running in open loop with a cold engine then I might expect it to work much like before the thermostat was changed and be less likely to stall at idle.
So that might point towards the issue.


I would be inclined to take a Neanderthalic approach to this and rather than thinking that the scanner is going to give you all the answers (if its a cheap one from HongKong the information it gives is going to be limited to just reading out codes)

Instead I would take the air box off, run it on the drive without the airbox, to answer the question 'is the engine getting enough air' if there is a restriction in the air box or filter this might affect idle.

The engine and valves might be badly coked up if its been running badly for some time, so I would then spray a can of carb cleaner into the throttle body while the engine is running (not all in one go, short little bursts) if there is a lot of build up on the valves then they might be restricting airflow.

So once you have sprayed a can of carb cleaner into and left it running for a bit to burn off any residual cleaner turn the car off.
Locate the fuse for the ECU and pull it.
Walk a way and have a cup of tea for an hour.

This should reset the parameters of the ecu to a default setting. no different to turning your computer off and on again when it stops working or crashing.

This will set the cars ECU to a sort of safe mode that will operate the engine, slightly less efficiently but without issue. It then needs time in closed loop, to learn the best way to handle the fueling and idle of the engine, so taking for a long run. (probably put the air box and filter back on)

Other things to check (panda people will have to help me here) is the mass airflow sensor in the airfilter box, is there an intake air temperature sensor on these? are these sensors plugging in and working if the mechanic took the airbox off he might have damaged one of these or not plugged them back in correctly.

I think if you can do these things over the weekend you probably wont need to worry about the code reader and you might well solve your problem. If not you have the added back up of the code reader coming and you can then see if it is throwing up any errors.

I think its unlikely the button or the compressor is causing the issue. and I think 800rpm might be fine as idle with the AC off and ie no load on the engine and a nice warm engine running closed loop but I's expect it to be higher when the engine is cold and operating in open loop.