Car AC Diagnosis of Various Symptoms Dedicated Thread

[wasim625]

So errmm talked about the above isue with my mechanic (he is a mechanic and not a full time AC wala) he say my ride has combine AC thermoswitch and engine coolant temperature sensor. The clutch disengaged because that was top peak heat outside at that time engine was too hot and as my both switched are combined the clutch for the compressor was not engaging. Later on when the temp. Came down it started to engage normal.

My question::
Why engine temp is important for AC clutch to operate or not to operate. It would have made sense if he told me about Cabin temp. Sensor was not allowing the clutch to engage.

2: if my engine temp was too high for AC clutch to engage then why the Heat Needle was between the optimum engine temp. Range it should be above optimum temp. by that theory.

[afnan.bashir]

Yes But On Pressure Gauge You Have To Exactly Do It In Order Not To Overcharge....It Can Also Increase Suction And Will Also Make U See Your Extreme Head pressure

If You Charge By Weight...You Can Just Charge Slowly But Revving Is Recommended .....Its MUST If You DOn't Know Quanity To Charge And Totally Depending On Manifold Gauge Set Readings

Still why do we check head pressure at 1500 rpm. Not while charging but why is head pressure at idle low. Question is that is there some mechanism that regulates pressure at various rpms for example of you drive car at 1500 rpm the compressor put 200 psi but if you floor the throttle and it goes to 600 rpm then what compressor puts 400 psi? of course there is pressure switch for a purpose

[afnan.bashir]

So,
Today i noticed at peak 2 p.m my car's AC stopped working. It was like clutch was not all the way engaging. It engages at IDLE rpm and when i press accelerator it disengages and never engages back. This problem is there when car is stopped.
Once car is on highway running at any speed the AC behaves normal.
To me that looked like the condensor was unable to dissipate heat from the refrigerant and which ended up less cooling effect inside the cabin. Moreover, i couldn't get why the clutch was only engaging at idle RPM any RPM above idle disengage the clutch. It is normal by the way but the problem is once it disengages it engages back on its own will lol i mean any time it likes to. What i think is it should disengage and then engage back to start cooling but at that time 2 p.m it wasnt.
Later at 5 pm it was again behaving normally like nothing happened LOL

I believe your system is oversharged. Disengage can be cause by pressure switch.

[afnan.bashir]

So errmm talked about the above isue with my mechanic (he is a mechanic and not a full time AC wala) he say my ride has combine AC thermoswitch and engine coolant temperature sensor. The clutch disengaged because that was top peak heat outside at that time engine was too hot and as my both switched are combined the clutch for the compressor was not engaging. Later on when the temp. Came down it started to engage normal.

My question::
Why engine temp is important for AC clutch to operate or not to operate. It would have made sense if he told me about Cabin temp. Sensor was not allowing the clutch to engage.

2: if my engine temp was too high for AC clutch to engage then why the Heat Needle was between the optimum engine temp. Range it should be above optimum temp. by that theory.

Well i think he is wrong. Coolant Temp Sensor is seperate and there is a sensor on high side that is seperate for cutoffs. Thermostat switch is at evapourator core it cant be outside. Which car you have

[wasim625]

Well i think he is wrong. Coolant Temp Sensor is seperate and there is a sensor on high side that is seperate for cutoffs. Thermostat switch is at evapourator core it cant be outside. Which car you have

I think that too.
The car is Hyundai Santro.

Apart from the mechanic's word. How will you interpret above problem?

[uxair.saeed]

salam guys I have a weird issue of gas leakage in Civic 2002. It happened through different points like o-ring of condenser, low pressure valve i.e located on small diameter pipe, dryer etc. A/C mechanic assumed that there is some sort of blockage in system so he suggested me to replace the condenser and dryer so i did. but this issue is not resolve and gas is again leaked through that valve. He permanently closed this miserable valve by soldering it and charged new gas But it did't last for two days and again leaked. Now that guy conclude that the cooling coil as well as gas lines are might be block and they should be replace at earliest. :o so please guide me

[SER_GTR]

Still why do we check head pressure at 1500 rpm. Not while charging but why is head pressure at idle low. Question is that is there some mechanism that regulates pressure at various rpms for example of you drive car at 1500 rpm the compressor put 200 psi but if you floor the throttle and it goes to 600 rpm then what compressor puts 400 psi? of course there is pressure switch for a purpose

There A Limit To This.....What You Need To Check Is Get Some RPMS To Compressor So All Ref. In System Circulates And Then You See A Head pressure....This Is Where It Normally Tells You If H.P Is Rising Or Not.....

With RPM's Kicking....You Check System Integrity As You Drive Normal....On Idle...Compressor Is Not Upto Its Maxx Nor System...

In Order To Check System Completely You Need To Raise RPM And Check It....!

[wasim625]

Any of the experts on my issue please?

[Xulfiqar]

Still why do we check head pressure at 1500 rpm. Not while charging but why is head pressure at idle low. Question is that is there some mechanism that regulates pressure at various rpms for example of you drive car at 1500 rpm the compressor put 200 psi but if you floor the throttle and it goes to 600 rpm then what compressor puts 400 psi? of course there is pressure switch for a purpose

the compressor itself has valve plates in it to control the intake volume, thats why you dont see a forever rising high side pressure, OTOH, new model compressors come with a volume control valve in the intake port, this valve allows bleedoff of the vapour to reduce compressor load and also head pressure. Testing such compressor with gauges can really make you scratch your head as the gauges start to act incredibly stupid if that valve is not functioning correctly.

Whilst charging its best to use a stick to raise the rpm to 1500 to ensure good suction of the refrigerant into the unit, once all the volume is injected then wait for about 10 minutes to let the unit stabilise and then retest. - Make sure the load on the evaporator is at max - open all doors, open the ventilator and set the blower to max and heater completely off.

then put a drum fan in front of the car to cool the condenser (not water).

[abdullah.sheikh.1848]

Any help regarding my issue???

[Xulfiqar]

So errmm talked about the above isue with my mechanic (he is a mechanic and not a full time AC wala) he say my ride has combine AC thermoswitch and engine coolant temperature sensor. The clutch disengaged because that was top peak heat outside at that time engine was too hot and as my both switched are combined the clutch for the compressor was not engaging. Later on when the temp. Came down it started to engage normal.

My question::
Why engine temp is important for AC clutch to operate or not to operate. It would have made sense if he told me about Cabin temp. Sensor was not allowing the clutch to engage.

2: if my engine temp was too high for AC clutch to engage then why the Heat Needle was between the optimum engine temp. Range it should be above optimum temp. by that theory.

your car has mitsubishi wiring, the AC is wired through the ECU, it has a factory cut off system at quick acceleration. It should re-engage at low load again, If its not then check the system run pressures, it also kills the A/C should the liquid line temperature get out of control.

It also will cut out the AC if the compressor pulley rpm is not stable (loose belt or wide clutch gap)

[wasim625]

your car has mitsubishi wiring, the AC is wired through the ECU, it has a factory cut off system at quick acceleration. It should re-engage at low load again, If its not then check the system run pressures, it also kills the A/C should the liquid line temperature get out of control.

It also will cut out the AC if the compressor pulley rpm is not stable (loose belt or wide clutch gap)

Bhai it does cut off at quick acceleration and engages back but at that time i-e 2 p.m peak heat it wasnt engaging back.

It engages back randomly and when ever it engages i could feel the air getting cold.

Every thing went normal an hour and half later when weather temp dropped a bit.

What could have been the issue that time?

(From your post i guess it could be irregular/unstable high line temp. as it was heat outside) your final verdict please.

[Xulfiqar]

as afnan said - I think too the system is going out of control, check the condenser fins for debris and also check the volume of the refrigerant.

[wasim625]

as afnan said - I think too the system is going out of control, check the condenser fins for debris and also check the volume of the refrigerant.

Ok. I'll pull R134a ambient Temp. Vs Pressure Chart and hook the guages to check what going on in there and report back.

[afnan.bashir]

Hello everyone. I recently got my ac serviced and gas refilled. Its working very well, even in the afternoon with the temp higher than 42c its extremely chilly, but the issue is its not cooling on idle and when the ac is on the rpm gets unstable and goes very low and the car vibrates bcz of a shaky rpm and with the ac on the car gets a really heavy. The car is a 2000 model Honda civic vti oriel. Help would be really appreciated

I am sure your system was done traditional way. Low cooling on idle can be caused by either a low refrigerant or weak compressor. If you feel load and idle drop with no cooling on idle then this means your compressor is weak. You need to do high side and low side pressure readings. Hold your car at 1500 RPM and note the pressure and ambient temperature. I am writing a diy on AC stuff charge it according to that procedure.

[Xulfiqar]

there is another problem to address..

lack of oil charge in the units, usual ac mechanics in Pakistan think that the whole unit only holds 2 tablespoons of oil. Its wrong. low oil can cause rapid wearout of the compressor.

Low charge also can kill some compressors as oil does not travel fast enough back to the compressor, e.g. sanden compressors have an oil sump in them and almost always have an oil reserve to work with, the newer scroll units and the variable intake compressors solely rely on refrigerant to carry the oil.

[wasim625]

@xulfiqar
Bhai what do you think:
- does AC clutch dis engages if engine coolant temp is out of control? Is it even dependant on ECT?

• my mechanics shows me a wire in suzuki cultus at says this is AC compressor temp wire. Compressor senses engine temp by the wire. Is it possible?

[anc]

Would it help increase the cooling of AC if we block the Heater pipes?

Would someone please shed some light on this

[Xulfiqar]

@Xulfiqar
Bhai what do you think:
- does AC clutch dis engages if engine coolant temp is out of control? Is it even dependant on ECT?

- my mechanics shows me a wire in suzuki cultus at says this is AC compressor temp wire. Compressor senses engine temp by the wire. Is it possible?

That wire is the overheat cutoff switch - he is correct to show you that. That wire in the suzuki system is very simple, on denso style system its a 2 wire switch that opens up when the coolant is very hot, on sanden style its clamped to the water pump intake pipe.

[Xulfiqar]

Would someone please shed some light on this

no it wont, the heater is only active if you select the heat position on the control panel.