A/c shuts down after buzzing noise but noise continues. Heater booster pump?

[Nightdriver]

It's seems my heater blower A/C problem is getting worse the ac now randomly shuts down all together. And will restart when it wants. The buzzing noise seems to be coming from the engine compartment not from the blower heater fan. A heater booster pump is now the suspected culprit as the noise and vibrations seems to be coming from here.

 

[lexman8]

Is it just the aircon that's switching off or the whole climate system? If it's just the aircon going off, then that could be caused by a number of issues such as a faulty sensor or low refrigerant pressure. A faulty electric circulation pump on the heater system would not, on its own, cause the aircon to switch off.

The electric circulation pump is located just in front of the rearmost engine bulkhead, near the wiper mechanism. If your car has the REST function you can check if the buzzing is coming from the electric pump by switching off the engine and engaging REST. This will cause the electric pump to switch on. With the engine off you should be able to easily hear if the buzzing is coming from the electric pump.

 

[Nightdriver]

Is it just the aircon that's switching off or the whole climate system? If it's just the aircon going off, then that could be caused by a number of issues such as a faulty sensor or low refrigerant pressure. A faulty electric circulation pump on the heater system would not, on its own, cause the aircon to switch off.

The electric circulation pump is located just in front of the rearmost engine bulkhead, near the wiper mechanism. If your car has the REST function you can check if the buzzing is coming from the electric pump by switching off the engine and engaging REST. This will cause the electric pump to switch on. With the engine off you should be able to easily hear if the buzzing is coming from the electric pump.

The buzzing is deffinately coming from the electric pump as you say. But what do you think is switching off the AC. It's just the Av heater/fan that goes off then will start again, I noticed it goes off when idle at lights eğ but 2 ill eventually start again, the electric pump does not go off when AC does. Strange?

 

[Nightdriver]

The buzzing is deffinately coming from the electric pump as you say. But what do you think is switching off the AC. It's just the Av heater/fan that goes off then will start again, I noticed it goes off when idle at lights eğ but 2 ill eventually start again, the electric pump does not go off when AC does. Strange?

"Low refrigerant pressure" not sure but I do notice moisture on the outside öf windscreen when AC is cold.
P's the pump is silent when set at coldest point.

 

[lexman8]

On max cooling there's no need for the electric pump in the heating circuit so it might get switched off.

I'm unclear as to whether the problem is the aircon (i.e. cooling) going off or just the cabin blower fan?

When the engine is idling and electrical demand is high the voltage can drop if there is a problem with the battery, alternator or charging circuitry. If this happens, the blower fan, along with other non-essential consumers, will be switched off when the low voltage is detected. This is to ensure that essential circuits such as ABS or ignition remain operating. Normally, a warning will appear briefly on the dash display saying something like 'Consumers not available'. It only appears for a couple of seconds. Since you say the blower seems to go off when idling but then comes back on, perhaps the problem is voltage related. Is the battery in good condition and fully charged?

So there could be 2 separate problems: the electric pump (this isn't absolutely essential to the working of the climate system other than for the REST function) and the cabin blower fan. Moisture on the outside of the screen suggests the actual aircon is working.

 

[Nightdriver]

On max cooling there's no need for the electric pump in the heating circuit so it might get switched off. I'm unclear as to whether the problem is the aircon (i.e. cooling) going off or just the cabin blower fan? When the engine is idling and electrical demand is high the voltage can drop if there is a problem with the battery, alternator or charging circuitry. If this happens, the blower fan, along with other non-essential consumers, will be switched off when the low voltage is detected. This is to ensure that essential circuits such as ABS or ignition remain operating. Normally, a warning will appear briefly on the dash display saying something like 'Consumers not available'. It only appears for a couple of seconds. Since you say the blower seems to go off when idling but then comes back on, perhaps the problem is voltage related. Is the battery in good condition and fully charged? So there could be 2 separate problems: the electric pump (this isn't absolutely essential to the working of the climate system other than for the REST function) and the cabin blower fan. Moisture on the outside of the screen suggests the actual aircon is working.

Took out the blower to give it a clean and check regulator for water damage but looks new and all seems to be working find. The electrical pump seems to be working as I can hear it and can feel it working when I touch it. However I now suspect the change-over valve (or shut off valve) below windscreen. I'm guessing hot water is not going through to the inside of the car to allow blower to blow it in. Will flush it out when I take it off in case of lime scale or debris build up from what I gather it is not an expensive part to replace. My battery is new, alternator 12 months old and water pump is new as is my main cooling fan.

 

[Nightdriver]

Took out the blower to give it a clean and check regulator for water damage but looks new and all seems to be working find. The electrical pump seems to be working as I can hear it and can feel it working when I touch it. However I now suspect the change-over valve (or shut off valve) below windscreen. I'm guessing hot water is not going through to the inside of the car to allow blower to blow it in. Will flush it out when I take it off in case of lime scale or debris build up from what I gather it is not an expensive part to replace. My battery is new, alternator 12 months old and water pump is new as is my main cooling fan.

i am still baffled as to what may be cutting out the ac ie the fan goes off and will restart again some time later and will decide to blow cold instead of hot.

 

[lexman8]

Lack of heat could be caused by a number of things:

• faulty duo valve (that's the one below the windscreen)
• failure of a temperature sensor (there are several of them)
• failure of the climate ECU
• CAN problem

You can check the duo valve by setting the controls for maximum heat and touching the 3 water pipes connected to it. All 3 should be hot.

 

[lexman8]

i am still baffled as to what may be cutting out the ac ie the fan goes off and will restart again some time later and will decide to blow cold instead of hot.

Does the fan work correctly (ie keep running) if you select a manual fan speed?

 

[Nightdriver]

Does the fan work correctly (ie keep running) if you select a manual fan speed?

The fan was working fine at all levels until it cut out at 85c, about 30 minutes later it came back on and was blowing cold. For hours.
Today however the heat is back and it hasn't shut down. I'm happy but puzzled. On touching the valve one pipe is cooler than the others.

 

[lexman8]

When both cabin temperature controls are set to max heat, both outlet pipes on the duo-valve should be the same temperature.

When it's blowing cold, is it on both sides of the car?

 

[Nightdriver]

When both cabin temperature controls are set to max heat, both outlet pipes on the duo-valve should be the same temperature.

When it's blowing cold, is it on both sides of the car?

Ok this is getting strange. I haven't had a chance to flush the system & pipes but all of a sudden after freezing cold för two days the heating is back as if nothing happened. Now I'm confused.
Yes when it was cold it was on both sides of car

 

[lexman8]

Yes when it was cold it was on both sides of car

Could be a sensor problem.

Do you know how to access the climate system diagnostics on your car? Here's how to do it on my CL. Your car may be similar.

Turn the ignition key to position 2 or (preferably) have the engine running and aircon switched on. Set the temperature on both sides of the car to, say, 15C. Then put the climate system into diagnostic mode as follows. If you have a REST button on the climate system press it for >5 secs. If you don't have a REST button press the AUTO button on the driver's side for >5 secs. This should enable diagnostics.

Use the passenger side temperature up/down button to scroll through the parameters that are displayed. Your car's parameters may be different from mine but here's what the first 8 on mine show:

NR.00: In Car Temperature Sensor ACC Pushbutton Control Module Front Compartment
NR.01: In Car Temperature Sensor Overhead Control Panel (OCP)
NR.02: Outside Temperature Sensor
NR.03: Heater Core Temperature Sensor Left Front Compartment
NR.04: Heater Core Temperature Sensor Right Front Compartment
NR.05: Evaporator Core Temperature Sensor Front Compartment
NR.06: Engine Coolant Temperature Sensor
NR.07: Refrigerant (R134A) Pressure Sensor
NR.08: Refrigerant (R134A) Temperature Sensor

All temperatures are in Celsius and pressures in bar. There are nearly 100 parameters in total.

Check to see if the values for the first 3 parameters are what you would expect. Also check parameters NR03 and NR04. The left and right heater cores are fed water from the duo valve and if it's working correctly these should be within a couple of degrees of each other when the left/right cabin temperature settings are the same.

Here's the problem I have.

The heating works for the first 20 mins or so then goes cold. I've traced the problem to the lower temperature sensor in the climate control unit. The sensor there (and the one in the OCP) has a small fan that draws air from the cabin across the sensor so as to give an accurate air temperature reading. The fan on mine has failed so after a while the sensor reports a high temperature to the climate ECU. It then turns the heating off because it thinks the cabin temperature is 30+ degrees.

If your problem is like mine, the car may have to have been running a while before one of the sensors gives a false reading.

 

[lexman8]

See also post #11 here:

http://www.mbclub.co.uk/forums/electronics/181558-climate-issue-air-footwell.html

 

[Nightdriver]

See also post #11 here:

http://www.mbclub.co.uk/forums/electronics/181558-climate-issue-air-footwell.html

That doesn't seem to work on my s320. There may be another combination to check my sensors.
But it now seems to have shut down completely, it's been several hours now. It deff is an electrical issue but where?