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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3567
Experience:  Qualified Mercedes Benz Diagnostic Technician - 20+ years experience - Workshop Foreman for Mercedes
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2001 MB C240 a/c no cooling at idle rpm; cools at 40 mph.

Customer Question

2001 MB C240 a/c no cooling at idle rpm; cools at 40 mph.
JA: How many miles are on the car? What size is the engine?
Customer: 96k 6cyl (engine cooling fan working good)
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: system evacuated and recharged; good pressures
JA: Anything else you think the mechanic should know?
Customer: same problem year ago. mechanic changed compressor didnt work afterward.
Submitted: 4 months ago.
Category: Mercedes
Expert:  Kalamykid replied 4 months ago.

Do you have the car with you now? Do you have time to check few things?

Expert:  Kalamykid replied 4 months ago.

The first thing you need to check will be the electric fan for the radiator. If the fan does not come on on high, with the ac on, then the condenser will not be cooling off.

Customer: replied 4 months ago.
I will have to respond later when the vehicle nearby.
Expert:  Kalamykid replied 4 months ago.

OK. Just let me know when you would like to have look at it.

Expert:  Kalamykid replied 4 months ago.

ok

Customer: replied 3 months ago.
Medical delays. Segmented dialog may be necessary. Radiator fan is operating with a/c turned on.
Customer: replied 3 months ago.
Medical delays. Segmented dialog may be necessary. Radiator fan is operating with a/c turned on.
Expert:  Kalamykid replied 3 months ago.

Just let me know when you can get back to work on this problem.

Customer: replied 3 months ago.
I have time now; however, being at the computer, I'm not near the auto. Which also
means that our dialog may be temporarily delayed should I need to inspect the car
to provide answers to your query.
The radiator fan is working while the a/c is on.
Expert:  Kalamykid replied 3 months ago.

Do you have a set of ac gauges? We will need to know what the high and low side pressure readings are.

Customer: replied 3 months ago.
No. Twice, somewhat recently the system has been checked (by "professionals") for leaks, evacuated, refilled, and re-tested,
Before the last such action: 1. the pressures indicated no leaks since the first mehcanic's work, and 2. the radiator fan was replaced because the mechanic said the fan was weak. So a new fan was installedbefore the evacuation and refilling: of course with same inoperative a/c result. However, after the last (2nd mechanic's) work, the system responded
slightly different. On a trip of about 40 miles, the unit was cooling well even upon stopping, and then in slow traffic continued to cool through acceleration and maintained higher road speed. Then later, it ceased to function at low road speed. And
now,again, it doesn't work at idle or low road speed, and requires higher than 40 mph speed to operate. So, since there was no indication of leak between the first and second mechanic's work, I have reason to believe that the system is properly filled.
Expert:  Kalamykid replied 3 months ago.

If the high side pressure gets to high the system can DUMP freon out. For this reason we need to know what the high and low side readings are. These reading will also tell me why the system is not cooling at idle.

Customer: replied 3 months ago.
On Monday 15th I will check with last mechanic to hopefully provide accurate data from his work and then respond to you.
Expert:  Kalamykid replied 3 months ago.

I need to know what the readings are at idle and at 2000 rpms please.

Customer: replied 3 months ago.
Delayed response because I am undergoing 7 week of radiation, and ensuing issues. Thanks
for your patience and help.
Both previous mechanics have no recorded data for 2000 rpm readings. One responded that
the readings for both high and low pressure were within acceptable limits.
Day before yesterday the a/c began cooling at low vehicle speed and continued through higher speeds.
Should I be able to obtain psi readings at 2000 rpm, what would be reasonable? Or, without obtaining
those readings, what might be an alternate step?
Expert:  Kalamykid replied 3 months ago.

Will it still cool at low speeds? Will it cool at idle?

Customer: replied 3 months ago.
Not cooling at low speed. Cools starting at 50-60 mph.
With erratic, but seldom cooling at low speeds, would pressure readings help define the source problem?
Is there an internal construction, such as within the coolant tubing be a possible source; or, perhaps and
loose/partially broken electrical wire or internal control switch?
Twice the unit has cooled at low speed; on both occasions the ambient temperature was in the low 80's.
Is that significant?
Expert:  Kalamykid replied 3 months ago.

Yes the high and low side readings are very important to be able to see why the system is not working correctly. Can you get a set of a/c gauges please so we can find and fix this problem? I promise it will be worth it, and I can walk you through all the steps to fix this.

Customer: replied 3 months ago.
I will pursue getting the readings. Thanks
Expert:  Kalamykid replied 3 months ago.

If you get a set of gauges we will be able to work together. The set of gauges will cost you less then $40.00 and there are more then 10 readings needed to pin down the problem.

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