Air Con: 70: - '98 S70 Bizarre A/C Issue ;-0

M Miller · Jan 13th, 2008, 04:31

Hi Folks;

I'm an A/C tech and have been working on a '98 S70 :-(

The evap was replaced, the compressor (due to mileage), accumulator, orifice tube etc.

System has exact amount of oil & refrigerant. The system was evacuated to 750 microns and checked for leaks under both vacuum and pressure. It's hermetically sealed and blows ice cubes. All controls work perfectly - in short - it's better then new - literally.

The problem is this - the compressor clutch will not engage when you drive the car. The A/C only works when the vehicle is at idle. I believe this to be a pre-existing condition but can't figure out what would cause it other then possibly a pooched ECC module.

We looked at two thermistors located at the very front of the vehicle in the lower grills. Both are now 100% clean with no corrosion-induced resistance. Also, both thermistors specced out the same given the ambient - we know they are good.

Any ideas why that clutch only engages at idle? Also, the clutch gap is spot on and it's a 100% new OEM unit that works perfectly. Methinks we've got some kind of wierd electrical issue here ....

Georgey dee · Jan 13th, 2008, 11:18

Could it be because of the temperature. The system is protected by a thermometer and will not engage below 0 degs.

Clan · Jan 13th, 2008, 11:38

Have you checked with a test light that there is a good feed to the clutch when the engine is driving and compressor not working ? Does the clutch disengage when you rev the engine?

The Engine ECU is in control of the Compressor not the climate module directly . it operates the compressir relay when it gets a request from the climate module and as it monitors the AC pressures only when the pressures are right . Perhaps the pressure is too high? ie. wrong gas ? R134a is the gas . Wrong compressor with too high a capacity ? You said it was not a volvo specification compresssor ...

M Miller · Jan 13th, 2008, 21:19

Hi guys;

Many thanks for the replies!

The ambient temperature up here (at time of testing) was 8c. According to Mitchell the system won't engage at 0 or below. The instrument cluster shows the ambient temperature and was also reading 8c - it's accurate as we cleaned and tested those two thermistors so ambient temperature should not be an issue.

With regards to the compressor operating in the shop - we haven't yet tested to see if it will operate if the RPM is higher (such as 2,000 RPM). That's on our list of things to check - thank you for bringing it up - it's a valid point.

With regards to the compressor - it's a 100% new Volvo part. Not used, not reman, not another brand - it's new Volvo.

R134a is the refrigerant used - specifically 26.4 ounces. The system is hermetically sealed - it's as new or better.

The issue must be electrical or ECC or something along those lines. As soon as I get a chance we'll test for compressor operation at above idle in the shop and will post back the results.

Thank you both for your replies - they are shedding light on aspects of the job and causing us to think in new ways

Chris_Rogers · Jan 13th, 2008, 22:07

The use of a Volvo scan tool would help, the AC pressure, as seen by the engine ECU, and AC request from ECC can be displayed as live data.

You could also monitor the AC pressure transducer output & the DC input to the compressor using a multimeter.
You may find that to AC is shut off at higher pressure/RPM by the engine ECU.

28.8 oz = 816 grams which is a little on the high side, from memory the fill wieght should be 750 grams. However I doubt the difference is significant.

M Miller · Jan 14th, 2008, 03:31

Hi Chris;

With regards to the charge spec - I actually used 26.4 ounces which is the factory spec.

Today we swapped the A/C relay for another unit from a known functional vehicle and encountered the same issue - A/C works at idle and not on the road.

We also tried running the engine at 2,000 RPM in park to see if that would cause it to act up - no difference - the A/C works perfectly in the shop (or at a light).

I don't have a Volvo scan tool - will a modern Snap-on unit also show the HVAC system?

Is there a special 'reset' procedure for these vehicles?

Alec Dawe · Jan 14th, 2008, 08:05

Could this be a mechanical problem rather than an AC problem
I believe that the magnetic clutches on the compressor can go out of adjustment, and somewhere on the forum is a set of instructions on how to adjust the clutch gaps to get everything working again.
Not sure if this would give the symptoms you describe, but might be worth a hunt and a check of the clutch?

M Miller · Jan 14th, 2008, 08:06

Good point - I considered that originally and checked the clutch gap - it's spot on :-(

Alec Dawe · Jan 14th, 2008, 08:11

How about the cabin temperature sensor. I believe that the little grille to this can get blocked, fooling the air con into thinking everything is good?

jeremycolley · Jan 14th, 2008, 13:48

Hi - this article might help

http://au.geocities.com/ozbrick850/aircon-keithP.html

Does the compressor cut out when the revs are increased above idle or when the car is in motion?

A quick scan of this article reveals that the compressor is shut down at WOT - unlikely, but could the TPS be throwing an incorrect reading above idle (whilst not triggering a number of other syptoms or faults)..?

Jeremy

Jan 13th, 2008, 04:31	#1
M Miller New Member Last Online: Feb 5th, 2008 03:25 Join Date: Jan 2008 Location: Parksville	'98 S70 Bizarre A/C Issue ;-0 Hi Folks; I'm an A/C tech and have been working on a '98 S70 :-( The evap was replaced, the compressor (due to mileage), accumulator, orifice tube etc. System has exact amount of oil & refrigerant. The system was evacuated to 750 microns and checked for leaks under both vacuum and pressure. It's hermetically sealed and blows ice cubes. All controls work perfectly - in short - it's better then new - literally. The problem is this - the compressor clutch will not engage when you drive the car. The A/C only works when the vehicle is at idle. I believe this to be a pre-existing condition but can't figure out what would cause it other then possibly a pooched ECC module. We looked at two thermistors located at the very front of the vehicle in the lower grills. Both are now 100% clean with no corrosion-induced resistance. Also, both thermistors specced out the same given the ambient - we know they are good. Any ideas why that clutch only engages at idle? Also, the clutch gap is spot on and it's a 100% new OEM unit that works perfectly. Methinks we've got some kind of wierd electrical issue here ....

Jan 13th, 2008, 11:18	#2
Georgey dee Premier Member Last Online: Feb 14th, 2024 18:36 Join Date: Dec 2005 Location: Norwich View Photos By: Georgey dee	Could it be because of the temperature. The system is protected by a thermometer and will not engage below 0 degs. __________________ HAD; 440 GLT(Loved it), 850 GLT auto(Loved it), S70 2.5T(Nothing but problems!), 850R auto(Loved it!!), S60 D5 SE (Nothing but problems!) GOT; S60 D5 SE Lux Auto RAF Marham Track Day Co-Ord'

Jan 13th, 2008, 11:38	#3
Clan Experienced Member Last Online: Today 11:14 Join Date: Jun 2007 Location: L/H side	Have you checked with a test light that there is a good feed to the clutch when the engine is driving and compressor not working ? Does the clutch disengage when you rev the engine? The Engine ECU is in control of the Compressor not the climate module directly . it operates the compressir relay when it gets a request from the climate module and as it monitors the AC pressures only when the pressures are right . Perhaps the pressure is too high? ie. wrong gas ? R134a is the gas . Wrong compressor with too high a capacity ? You said it was not a volvo specification compresssor ... __________________ My comments are only based on my opinions and vast experience .

Jan 14th, 2008, 08:05	#7
Alec Dawe Former Support Team Last Online: Jan 26th, 2024 11:26 Join Date: Jan 2006 Location: Nr Norwich	Could this be a mechanical problem rather than an AC problem I believe that the magnetic clutches on the compressor can go out of adjustment, and somewhere on the forum is a set of instructions on how to adjust the clutch gaps to get everything working again. Not sure if this would give the symptoms you describe, but might be worth a hunt and a check of the clutch? __________________ Alec. (My other car is a WD 2-10-0)

Jan 14th, 2008, 08:11	#9
Alec Dawe Former Support Team Last Online: Jan 26th, 2024 11:26 Join Date: Jan 2006 Location: Nr Norwich	How about the cabin temperature sensor. I believe that the little grille to this can get blocked, fooling the air con into thinking everything is good? __________________ Alec. (My other car is a WD 2-10-0)

Jan 13th, 2008, 21:19	#4
M Miller New Member Last Online: Feb 5th, 2008 03:25 Join Date: Jan 2008 Location: Parksville	Hi guys; Many thanks for the replies! The ambient temperature up here (at time of testing) was 8c. According to Mitchell the system won't engage at 0 or below. The instrument cluster shows the ambient temperature and was also reading 8c - it's accurate as we cleaned and tested those two thermistors so ambient temperature should not be an issue. With regards to the compressor operating in the shop - we haven't yet tested to see if it will operate if the RPM is higher (such as 2,000 RPM). That's on our list of things to check - thank you for bringing it up - it's a valid point. With regards to the compressor - it's a 100% new Volvo part. Not used, not reman, not another brand - it's new Volvo. R134a is the refrigerant used - specifically 26.4 ounces. The system is hermetically sealed - it's as new or better. The issue must be electrical or ECC or something along those lines. As soon as I get a chance we'll test for compressor operation at above idle in the shop and will post back the results. Thank you both for your replies - they are shedding light on aspects of the job and causing us to think in new ways

Jan 13th, 2008, 22:07	#5
Chris_Rogers VOC Member Last Online: Apr 10th, 2017 16:55 Join Date: Jan 1970 Location: South Kent Coast	The use of a Volvo scan tool would help, the AC pressure, as seen by the engine ECU, and AC request from ECC can be displayed as live data. You could also monitor the AC pressure transducer output & the DC input to the compressor using a multimeter. You may find that to AC is shut off at higher pressure/RPM by the engine ECU. 28.8 oz = 816 grams which is a little on the high side, from memory the fill wieght should be 750 grams. However I doubt the difference is significant.

Jan 14th, 2008, 03:31	#6
M Miller New Member Last Online: Feb 5th, 2008 03:25 Join Date: Jan 2008 Location: Parksville	Hi Chris; With regards to the charge spec - I actually used 26.4 ounces which is the factory spec. Today we swapped the A/C relay for another unit from a known functional vehicle and encountered the same issue - A/C works at idle and not on the road. We also tried running the engine at 2,000 RPM in park to see if that would cause it to act up - no difference - the A/C works perfectly in the shop (or at a light). I don't have a Volvo scan tool - will a modern Snap-on unit also show the HVAC system? Is there a special 'reset' procedure for these vehicles?

Jan 14th, 2008, 08:06	#8
M Miller New Member Last Online: Feb 5th, 2008 03:25 Join Date: Jan 2008 Location: Parksville	Good point - I considered that originally and checked the clutch gap - it's spot on :-(

Jan 14th, 2008, 13:48	#10
jeremycolley Senior Member Last Online: Apr 18th, 2024 23:48 Join Date: May 2007 Location: Norwich	Air Con article Hi - this article might help http://au.geocities.com/ozbrick850/aircon-keithP.html Does the compressor cut out when the revs are increased above idle or when the car is in motion? A quick scan of this article reveals that the compressor is shut down at WOT - unlikely, but could the TPS be throwing an incorrect reading above idle (whilst not triggering a number of other syptoms or faults)..? Jeremy

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