Hi,

1980 240D here.

Is there a way to test my ac pressure switch without removing it?
I don't want to lose my refrigerant.

I can only get my ac compressor to engage when I jump the leads.
All fuses and relays have been tested and are in working order.

I believe I have either lost all of my refrigerant or my pressure switch is bad.

Thanks.

Gauges would be needed...if the pressures are good when the switch is jumped then it would be safe to deem the switch bad. If the pressures are bad the refrigerant is lost/low.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Do I check the refrigerant pressure with the car running, and the ac on?

Or do I need to jump the leads of the pressure switch first and then check the refrigerant pressure with the car running and the ac on?

I know that if the refrigerant pressure is low the compressor won't engage, and if the pressure switch is bad the compressor won't engage either.

I am thinking that if the refrigerant pressure is good, it is probably going to be a bad switch.

Going to have someone check the pressure with a gauge tomorrow.

Refrigerant pressures need to be checked with the compressor engaged and running so in this case the switch will need to be jumped.

If there isn't refrigerant don't continue to run the compressor with the switch bypassed as refrigerant is what moves the oil in the system.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

First, you need to verify refrigerant pressure is at the correct vapor pressure for the ambient temp you are in.

An R12 or R134 vapor pressure chart will give you a target pressure to test for.

IF, AND ONLY IF, pressure is equal or above the chart for the ambient temp, it is safe to jump the pressure switch.

Zero other reason to jump the switch.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

There are normally 2 pressure switches installed in the receiver drier, one for the freon detection, one for the aux fan activation. I don't own a 240D so I am not sure whether the aux fan pressure sw is there.

Without running the car, measure the switches with a multimeter. The low pressure sw ( freon ) should be closed. The high pressure sw ( aux fan ) should be open. If both are open then it indicates no or low freon or faulty low pressure sw. You then need a pressure gauge to measure the freon pressure. The quiescent freon pressure is about 70psi. The freon switch closes at 2 bar or 29psi. If the gauge shows more than 29psi then the freon switch should close.

I hope this helps.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Thanks.

I checked the switch that activates the fan and there was no beep from my meter (open?)
Then I checked the pressure switch, and I got the same thing, no beep.
So, I leaked all of my refrigerant or a faulty pressure switch.

I am hoping for a bad switch. I just had all of the o-rings replaced and the system pressure checked, vacuumed and filled with oil and refrigerant 6 months ago. And it was working beautifully until recently.

Will get the pressure checked soon by a professional, but either way, it will need to be recharged? I am thinking once the pressure switch is removed you lose the refrigerant.

Do you know how to calibrate ( check ) you meter for continuity? If you touch the chassis, does it bleep? If it does then the switches are open circuit.

Pressure switch seldom go bad. So it is likely freon is low or almost empty. Get professional help and tell him to check for pressure and leak.

BTW: when you wrote you jump the leads, what do you mean? You jumped the compressor to make it run or you jump the low pressure switch? When you jumped the 'leads', how long? Normally jumping the leads, compressor leads, is okay if you are confident freon is ok. If you jump the low pressure switch then it is for a short time only or else the compressor could be damaged.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

A pro will be able to capture the refrigerant if there is any remaining. They can change the switch, evacuate the system to boil out moisture and recharge. Unless the receiver dryer is new, I'd replace it.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

If you seek professional help and found to be low or no freon then remind them to pressurize the system to look for leak. If they don't then you will be back to here 6 months later. Good luck.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

X2, a pro should pressure test the system with nitrogen. Holding a vacuum is to boil out moisture and if it holds a vacuum well that is a good sign; BUT, it isn't a substitute for a pressure test.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thank you.

I only ran the compressor for 2 or 3 seconds by jumping the leads to the pressure switch.

I had the system pressure checked and it was good 6 months ago. All of the o-rings were replaced. I will need to find the leak. Maybe the o-ring of the pressure switch, that one was not changed.

Does anyone know of a stop leak that can be used with enviro safe or frosty cool refrigerant if I decide to go that route?

All snake oil is always temporary, no one knows how temporary is temporary. It is better to locate the leak and fix it. OTOH, it is not expensive to give it a shot. Unlikely to cause any harm.

Any leak has a tell tale sign, like a oily patch. If you suspect leak around the low pressure sensor then you may notice a wet oily patch near the receiver drier. Most likely is the compressor shaft o-ring or the condenser. If the leak is the evaporator inside the car then you are screwed. Very difficult/expensive to replace. I think I have spilled my gut. Good luck.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Thanks.
Is getting to the evaporator in the car very time consuming? Is that what makes it a difficult repair?