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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 29118
Experience:  Over 15 years experience as a Mercedes dealer technician
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Ac will not blow cold high side and low side are equal

Customer Question

ac will not blow cold high side and low side are equal pressure like compressor is not working
JA: Have you checked the Freon level?
Customer: freon ok
JA: What is the model/year of your Mercedes?
Customer: 2009 gl450
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: checked freon ok hooke gauges up high and low side are equal at 110 psi compressor appears to be spinning but i do not think this compressor has a clutch it spins all the time
JA: Anything else you want the mechanic to know before I connect you?
Customer: i tried the ac on manual and automatic and have it on recirculate
Submitted: 2 months ago.
Category: Mercedes
Expert:  Pete replied 2 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

You are correct the compressor spins at all times.It has an internal clutch/plate that controls pressure and the ac operation.

What needs to be done from here is to have the fault codes read out of the heater/ac control assembly.There should be at least one code set that will help to diagnose and pinpoint this issue here.This has to be done with a fully compatible scan tool that can plug in and can communicate with all computers to see what codes are set.Once this is done the code is then diagnosed to locate and repair this fault then the code cleared out with the scan tool to allow the ac to resume.

On a Mercedes vehicle certain codes that can set due to faults can disable the ac from operating so the codes do need read out of the climate control head to locate this fault.

One common issue is the evaporater temp sensor sending a false signal needing replaced.I have seen this sensor cause this issue before several times.Even if you attempted to replace it to see if it resolves the fault the codes still need cleared out to allow the compressor to operate normally again.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated ( should be a link to click on here or above).You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 2 months ago.
i checked with snap on scanner had 4 codes 9404 9405 9408 9601 erased codes. also removed and checked freon amount and it had 2.68 ounces in it wich was correct recharged system turned ac on tested ac still no cold air it also set no codes and said that ac compressor was running at a 100 % high and low sides are still equal reading 140 looks like to me ac compressor is bad but would like your opinion thanks
Expert:  Pete replied 2 months ago.

O.k.,that is great to hear you did check codes and have gone through these checks/testing above.With no codes set and the control unit says the ac compressor is at 100% this does sound like the compressor itself has failed internally.If there was a circuit fault or sensor fault a code would have set.I have seen the compressor fail in the past before causing this issue here with it needing replaced.

Let me know if you need anything else and feel free to rate my help here or above ( should be a link to click on ) as this is how I receive credit for my time,this can be done at any time and you can still come back here and reply if needed.Your 5 star rating is appreciated

Thanks Pete