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Old 22nd February 2008, 16:36   #1
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Default M-800 A/C cools only above 2500 rpm

Guys one simple but complicated doubt.

Car : M-800
Mods: Free flow Exhaust & other stuff
Compressor : Sanden
Model : SD 7



My a/c was done recently after a long gap,

Cooling was great it went down upto 7.9 degrees at the service centre,

But later on, driving under city conditions the cooling seems to be lesser.

I drive the car at 2500 rpm the a/c starts cooling.

Earlier this was not the same, i presume? i never had headers than.

Thermostat is not a problem.

Condenser and the Compressor is serviced by a pro.

No leaks any where, pressure tested for 30 mins.

Solution required on this.
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Old 22nd February 2008, 18:14   #2
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i havent come across this issue in my dad's m800 ('98 Carb). what about the blower settings? have you turned the knob to cool air portion (blue part)? what about the airflow direction knob? is it on fresh-air mode? what about coolant level? what about the condition of the radiator?

i didnt get what you mean by - it starts cooling @ 2500rpm.

i think FFE has nothing to do with it(??) the headers and pipes are located at the front and shouldnt affect cooling.
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Old 22nd February 2008, 18:25   #3
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You seem to be low on the refrigerant gas.
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Old 22nd February 2008, 18:25   #4
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Blower settings correct.

Knob at cool air position.

Fresh Air Mode.

Radiator serviced 25000km back.

When my rpm meter shows a constant 2500rpm the cooling is good.
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Old 22nd February 2008, 18:28   #5
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Refrigerant gas just filled today morining.

Top up done by a pro.

Someone from Bangalore know Shaji A/c Works near that Mount Carmel road.?
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Old 22nd February 2008, 18:39   #6
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Default i aint an expert:

Quote:
Originally Posted by PAVAN KADAM View Post

Fresh Air Mode - set it to re-circulating mode and see the difference

Radiator serviced 25000km back - time for the next service IMO

When my rpm meter shows a constant 2500rpm the cooling is good - the radiator fan speed will be high IMO - better cooling
my answers are in bold - please see - i am not at all sure about the last point.
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Old 22nd February 2008, 19:43   #7
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Slightly OT : Whats the idling rpm for M800?

Was it running fine before ?

Is it better only at 2500 rpm or above it as well i.e. not good below 2500 but good above it ?

Try recirculating mode.
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Old 23rd February 2008, 10:55   #8
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Is the AC comp kicking in at idle with raised RPM? Does the AC radiator fan come ON at idle?

If yes, does it cool initially and then suddenly goes low. If so try switching off the AC comp alone and leave fan running for a while, then switch ON again. If AC is cooling then, the phenomenon is icing and you need to keep a manual thermostat to cut the comp off.
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Old 23rd February 2008, 11:32   #9
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Thanks for your inputs guys,

My setting is in Recirculating mode

M-800 idling is at 750 rpm

Idling with a/c on is 1250 rpm

Radiator running fine no need to service as its running fine, all the fins cleaned.

Thermostat is a problem as per my R&D,I've shorted the thermostat switch.

But the a/c totally stopped working, the compressor is not kicking now.

I think i need to take it back to the a/c mechanic and get this checked.

Some thing wierd happening with this a/c, lets hope for the best.
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Old 23rd February 2008, 11:36   #10
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Planet rocker

There's no speedo reading for the radiator servicing.

The radiator fan runs at a constant speed, there's no way in which the radiator fan increase its speed at higher engine rpms.

At higher rpms the compressor runs at faster speeds and not the radiator fan.

Anyways thanks for your inputs,

Taking the car back to the a/c mechanic.

Will keep u guys updated.
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Old 23rd February 2008, 11:43   #11
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Pavan, check the fuse also, i also suspect the thermostat and will recommend the knob type variable thermostat against fixed ones, since it will allow you to +/- the cut off temp. Its cheaper also

Talk to your AC mech for details.

And oops if its topped kicking in then it can be gas leak, bypass the pressure switch to see if comp kick in, again if you are not sure how to ask the mech.

Last edited by Jaggu : 23rd February 2008 at 11:45.
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Old 23rd February 2008, 11:49   #12
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I have the knob type thermostat fixed long time ago.

Must check about the fuse you are mentioning.

Better i have a check with the a/c mech.
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Old 23rd February 2008, 17:50   #13
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Quote:
Originally Posted by PAVAN KADAM View Post

M-800 idling is at 750 rpm

Idling with a/c on is 1250 rpm
Its 750 without AC
and 850 with AC.
1250 is too high.
And i too think its the fuse.AC mechanic by pass the fuse and check the AC.If something is wrong with the Fuse with the by pass the AC compressor will kick in otherwise not.

Last edited by humyum : 23rd February 2008 at 17:54.
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Old 24th February 2008, 18:18   #14
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Hate to say it, but it looks like your compressor is kaput. I thought the same before my opinion on gas level, but wanted to give that a try.
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Old 24th February 2008, 23:15   #15
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Default A/c Cooling

HI, PAVAN you have mentioned that your a/c sysytem was not operative for some time so i hope you have replaced the receiver drier (bottle like stuff) as moisture could have gone in. I allso require to know a few things first. since yours is a sanden unit and not the o.e Subros unit is your radiator fan 80watts or 120watts. Non a/c cars come with 80watts ,eventualy after airconditioning it should be upgraded to120watts, this increases the draft considerably and allso results in better cooling. The other point is about the location of the condensor ,in many after market installations the technicians fit the condensor undercarraige with additional fan, in your case since u have metioned fitment of free flow exhaust there is a posibility of the hot exhaust gas directed on the condensor.I would allso like to know the brand of the EVAPORATOR UNIT IN YOUR CAR. Lastly please try to give the low presure reading of the A/Csystem when the a/c is on at around 1100RPM with windows roled up after about 5min it should be around 30-35 psi
Quote:
Originally Posted by PAVAN KADAM View Post
Guys one simple but complicated doubt.

Car : M-800
Mods: Free flow Exhaust & other stuff
Compressor : Sanden
Model : SD 7



My a/c was done recently after a long gap,

Cooling was great it went down upto 7.9 degrees at the service centre,

But later on, driving under city conditions the cooling seems to be lesser.

I drive the car at 2500 rpm the a/c starts cooling.

Earlier this was not the same, i presume? i never had headers than.

Thermostat is not a problem.

Condenser and the Compressor is serviced by a pro.

No leaks any where, pressure tested for 30 mins.

Solution required on this.
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