A/C Problem - PeachParts Mercedes-Benz Forum

420benz · #1 09-07-2009, 05:59 PM

Warm air coming out of vents. Clutch does not engage. Mono Valve was rebuilt 3 years ago. Added one can of freon#12 last month,and was working fine. How can i bypass the low pressure switch to rule it out?

#2 09-07-2009, 07:30 PM

You should start by connecting or having connected a set of manifold gauges to see if you have a charge in the system. If you must, all you have to do is short the two connectors at the low pressure switch which will bypass the switch. Do this with the engine off and listen for the click. It could be that the engine must run for the CCU to trigger the connection. If this is the case, only touch the connectors together long enough to ensure that the clutch will work then disconnect them. DO NOT leave them together for any length of time because you may very well be running the compressor with no lubricant circulating.

A safer way to check the low pressure sensor is to simply use an Ohmmeter to see if it is closed. That is definitely the safest way.

420benz · #3 09-07-2009, 08:38 PM

Quote:

Originally Posted by LarryBible

You should start by connecting or having connected a set of manifold gauges to see if you have a charge in the system. If you must, all you have to do is short the two connectors at the low pressure switch which will bypass the switch. Do this with the engine off and listen for the click. It could be that the engine must run for the CCU to trigger the connection. If this is the case, only touch the connectors together long enough to ensure that the clutch will work then disconnect them. DO NOT leave them together for any length of time because you may very well be running the compressor with no lubricant circulating.

A safer way to check the low pressure sensor is to simply use an Ohmmeter to see if it is closed. That is definitely the safest way.

Did that. But without the compressor running,i got a very low reading.The system is charged.It might be time to convert from #12 freon. What would a good conversion cost?

#4 09-08-2009, 06:47 AM

Quote:

Originally Posted by 420 benz

Did that. But without the compressor running,i got a very low reading.The system is charged.It might be time to convert from #12 freon. What would a good conversion cost?

"very low reading" doesn't tell us anything. How much pressure did the gauges show?

420benz · #5 09-08-2009, 11:23 AM

Quote:

Originally Posted by LarryBible

"very low reading" doesn't tell us anything. How much pressure did the gauges show?

Readings:Hi side=85 Low side=88
Jumped wires to the low pressure switch,nothing.Just cannot get that compressor to kick in.

Richard Wooldridge · #6 09-08-2009, 11:41 AM

What that reading means is that it was in the mid 80's when you checked the pressure. Doesn't tell how good the charge is, but it is definitley good enough that the compressor should have started turning. Time to check voltages to the compressor clutch coil. I do not recommend "converting".

420benz · #7 09-08-2009, 11:51 AM

Quote:

Originally Posted by Richard Wooldridge

What that reading means is that it was in the mid 80's when you checked the pressure. Doesn't tell how good the charge is, but it is definitley good enough that the compressor should have started turning. Time to check voltages to the compressor clutch coil. I do not recommend "converting".

Just called local indy,and said the same thing,it may be an electrical problem. If i can get freon leak[if any] then i will keep the freon 12.I have one small can left. That stuff is very expensive.

#8 09-08-2009, 12:30 PM

Richard is offering very good advice. Stay with R12.

R12 is only slightly more expensive than any other refrigerant. Any expense you incur to change to another refrigerant will gobble up any savings that you might enjoy due to less expensive refrigerant.

Check for voltage at the clutch connector going to the compressor. It could be that the clutch itself is bad or needs adjustment.

The pressures you are reading are proper static pressures. Whether it has a few ounces or is full to the brim, those are the pressures to expect without the clutch engaged.

420benz · #9 09-08-2009, 02:47 PM

Quote:

Originally Posted by LarryBible

Richard is offering very good advice. Stay with R12.

R12 is only slightly more expensive than any other refrigerant. Any expense you incur to change to another refrigerant will gobble up any savings that you might enjoy due to less expensive refrigerant.

Check for voltage at the clutch connector going to the compressor. It could be that the clutch itself is bad or needs adjustment.

The pressures you are reading are proper static pressures. Whether it has a few ounces or is full to the brim, those are the pressures to expect without the clutch engaged.

The indy i called was my neighbor and owns MB motors [The indy Benzmac worked for] That is where i met Donny. He also said to stay with R20 i will have him look at it tomorrow. If it is mechanical i have no problems.When you ask me to mess with anything with wires,i am lost.
I will keep you all informed. Thanks