A/C refilled, and water temperature seems a bit high - PeachParts Mercedes-Benz Forum

hk20000 · #1 04-07-2007, 02:06 AM

hey guys.

Summer is coming along nicely and I went to refill up my A/C system (it blew only a bit cool before) and it blows cold now... but during the mechanic pumping in the freon I see the water temperature climb to 100C and stays there.

it's kind of scary to look at the gauge although the redline is 120C.....

he was only idling the car and occasionally running the revs up to about 1500rpm to pump the freon around.... the A/C was pumping nothing cold when the water temp is at 100C as well....

I drove it out of the lot and did some quick sprint around hitting 100km/h and the water temp falls back to like 80 or so and the cold air started coming in with A/C put at "LO" and "Auto"

is this normal phenomenon? Another worrying thing is the A/C fan does not run at 100C it starts running quite a few minutes after the water temp is at 100C...... is there anything wrong with my A/C fan thermostat?

car is a 1995 C220 w/ 215000km btw.

stevebfl · #2 04-07-2007, 09:01 AM

The Aux fan comes on due to engine temps somewhere above 100 C for engine temp. It comes on for AC when system pressure gets above about 290psi. Nothing in your description indicates a problem to me.

If your coolant temp is registering higher than you have experienced then it is something to watch out for even if it falls within accepted ranges as it seems to be.

hk20000 · #3 04-07-2007, 11:10 PM

so when I drive the car whether the A/C is on or not seems have great impact to water temp.

no A/C - running car keeps temp at 80C, stopping the car for a while makes it hit about 90C but no more

A/C on - running car temp is at 90C already, stopping the car at the lights will cause the water temp to creep up to 100C and then when you move along with some wind it'll cool back down but only to 90C level.

is A/C that much load to the cooling system???

stevebfl · #4 04-07-2007, 11:27 PM

Do you know how AC works? Using a manipulation of the latent heat of vaporization heat is removed from one heat exchanger (the evaporator in the dash) and moved to the other heat exchanger (the condenser - directly in front of the radiator).

So when the AC is cranking air that is expected to cool the radiator is first ran through a condenser which could possibly be over 300 degrees. Do you suppose that air is a little warmer when it hits the radiator than it would be if no AC action was taking place.

blackmercedes · #5 04-08-2007, 10:56 AM

I know on my 98 C230, when the AC is working hard, it is normal for the coolant temp to be at about 100C or so when sitting in traffic. Has always done that.

So, when you reactivated the AC system, it put increased load on the coolong system, hence you increase in coolant temps.

BTW, and the reason for my post, is I was wondering if you had found the leak of refrigerant for the AC system?

hk20000 · #6 04-08-2007, 04:43 PM

I don't think it's leaking it's 12 years old car with no maintenance records on it it probably just disappeared throughout the years.

I always thought the condenser is behind the radiator not in front? I guess I was wrong.

so the condenser could heat up the air to like 300C?? wow I could fry eggs with that temp....

Does your A/C still manage to blow cold if the water temp is sat at 100C?? Coz my A/C isn't doing much if the water temp is hot....It's working but in a significantly weaker way.

stevebfl · #7 04-08-2007, 04:52 PM

Here in Florida condensers get to 300 + degrees F and I know of no autos with the condenser behind the radiator, definitely no MBs.

hk20000 · #8 04-08-2007, 05:03 PM

ic.

how's your A/C doing with 100C water temp?? Mine isn't too happy about it.

Matt L · #9 04-08-2007, 05:04 PM

Quote:

Originally Posted by hk20000

Does your A/C still manage to blow cold if the water temp is sat at 100C?? Coz my A/C isn't doing much if the water temp is hot....It's working but in a significantly weaker way.
[/LEFT]

If this is when the ambient temperature isn't extremely high, these could be related, and simply mean insufficient airflow through the condenser and radiator. Make sure that the path for the air is clear and not obstructed by debris. Also check the electric fan and the mechanical fan clutch.

Arthur Dalton · #10 04-08-2007, 05:37 PM

As posted earlier, the aux fans have two triggers ..one is coolant temp and the other is a/c high side pressure...if you are slightly short on refrigerant you will not see a condenser air flow fan operate b/c the high side does not attain trigger pressure, but you can still have enough refrig to get cooling.
So, you wind up with some cooling, but a hot cond. due to no air-flow, specially at stop/idle. This translates to a high thermal load across the radiator and an increase in coolant temp range.
A quick test [ gauges should be used for a full test, but this will help you ] is to jumper the high pressure switch at the reciever/drier and see if the cond. fan comes on..if yes, then you have low refregerant/low high side pressure
[ not enough to trigger the fan]
If jumper results in no fan, then you have a fan electrical problem..For openers in this case, I would check the fuse on top of the a/c fan relay..[ behind fuse box, relay compartment]..another common possible is burnt wires at the pre-resistor behind the driver headlamp..both of these should be looked at if you have no fan w/jumper at reciever high pressure sw.
Don't confuse your fan coming on for high coolant temps with a fan coming on for a/c pressure ..they use the same fan, but entirely different sensors/relays/fuses... completely different circuits sharing the same fan motor/s

If you fan is being triggered by high coolant temp, it could be high b/c the a/c fan never comes on...increasing coolant temps

hk20000 · #11 04-08-2007, 05:54 PM

Quote:

Originally Posted by Arthur Dalton

As posted earlier, the aux fans have two triggers ..one is coolant temp and the other is a/c high side pressure...if you are slightly short on refrigerant you will not see a condenser air flow fan operate b/c the high side does not attain trigger pressure, but you can still have enough refrig to get cooling.

So what is a proper range for the aux fan to be triggered by hot radiator? 100C or even higher? Because I was there when the mechanic is hooking up the freon the fan only started spinning when the water temp gauge is pointing a bit higher than 100 (say 105?) And that's a bit late and discerning.

Quote:

So, you wind up with some cooling, but a hot cond. due to no air-flow, specially at stop/idle. This translates to a high thermal load across the radiator and an increase in coolant temp range.
A quick test [ gauges should be used for a full test, but this will help you ] is to jumper the high pressure switch at the reciever/drier and see if the cond. fan comes on..if yes, then you have low refregerant/low high side pressure [ not enough to trigger the fan]

likely to be caused by low freon level, yes?

Quote:

If jumper results in no fan, then you have a fan electrical problem..For openers in this case, I would check the fuse on top of the a/c fan relay..[ behind fuse box, relay compartment]..another common possible is burnt wires at the pre-resistor behind the driver headlamp..both of these should be looked at if you have no fan w/jumper at reciever high pressure sw.
Don't confuse your fan coming on for high coolant temps with a fan coming on for a/c pressure ..they use the same fan, but entirely different sensors/relays/fuses... completely different circuits sharing the same fan motor/s

The fan does run I'm just a bit concerned about how it is activated as late as 105C coolant temp. Is it also normal that every time u start the car from a long term parking the fan comes on momentarily (for about 20 seconds or so) for self testing?

Quote:

If you fan is being triggered by high coolant temp, it could be high b/c the a/c fan never comes on...increasing coolant temps

that's the major concern here, yes. Why is the fan activated so late if the A/C is off? 105C? That's alarmingly high compared to many cars I have touched.

hk20000 · #12 04-08-2007, 05:56 PM

Quote:

Originally Posted by Matt L

If this is when the ambient temperature isn't extremely high, these could be related, and simply mean insufficient airflow through the condenser and radiator. Make sure that the path for the air is clear and not obstructed by debris. Also check the electric fan and the mechanical fan clutch.

so if the ambient temperature is higher the fan will come on and try to keep the airflow going for better cabin cooling? Is that what you are implying?

Arthur Dalton · #13 04-08-2007, 06:43 PM

Quote:

Originally Posted by hk20000

So what is a proper range for the aux fan to be triggered by hot radiator? 100C or even higher? Because I was there when the mechanic is hooking up the freon the fan only started spinning when the water temp gauge is pointing a bit higher than 100 (say 105?) And that's a bit late and discerning.

Coolant temp cut-in spec is 105C
Many guys lower this by putting a resistor accross the coolant temp sensor.

likely to be caused by low freon level, yes?
Yes..that is why I mentioned the jumper test. I suspect you have no fan for a/c pressure system. Do the test to find out ...

The fan does run I'm just a bit concerned about how it is activated as late as 105C coolant temp. Is it also normal that every time u start the car from a long term parking the fan comes on momentarily (for about 20 seconds or so) for self testing?

that's the major concern here, yes. Why is the fan activated so late if the A/C is off? 105C? That's alarmingly high compared to many cars I have touched.

That is normal spec for that car..remember , the fan is only an aux aid to control extreme thermal taxation of the system..it is not there for normal operation..only when it is needed , as in high ambient temps , towing, stop/idle in traffic, etc. If it is not called for , it just does not come on.. but if your a/c fan is not coming on , then the coolant suffers the burden and that triggers the high fan. These are BOTH only system aids in controlling
temps and pressures when they are being taxed by adverse conditions..you can run an a/c all day long and never see the fan being called for b/c the high-side never gets into a high thermal load condition..see that all the time in Moderate climates..but in Fl, the fans should come on right away b/c of the high ambient temps/conditions ...so, if you have high ambient temps and the system does not get to high side pressure trigger spec, it that can have an effect on the coolant temp.... and this can be caused by a shortage of refrigerant...[enough in there to get the cond hot , but not enough to trigger the high pressure switch] ..so, do the high pressure sw jumper test to see if that fan even works......could be a simple as a fuse .
VERIFY FAN OPERATION......
You may have no problem at all, but I would want to know if fans are working when they should..
..

just-n-time · #14 04-09-2007, 03:04 PM

My concern in this mater is the gauge readings,what are they? It sounds to me as though you may be just a little light on your coolant charge. I say this because of the drop in cool air flow at idle or stopped at a light! JNT

Matt L · #15 04-09-2007, 03:50 PM

Quote:

Originally Posted by hk20000

so if the ambient temperature is higher the fan will come on and try to keep the airflow going for better cabin cooling? Is that what you are implying?

Well, not quite. If it's very hot out and you're stopped with the AC running, 100C is nothing to worry about unless the AC isn't performing properly (but you indicate that it is).

If it's not hot out, 100C is probably (just a bit) too high, and indicates insufficient airflow more probably than anything else.