AC low pressure switch

463 Views 8 Replies 4 Participants Last post by Bob Lincoln, 3 mo ago

wheelsport

Discussion Starter · 3 mo ago

I replaced the condensor on my 2010 Sebring. After doing a pump down, I have a small leak. I want to install some freon and sealer. However, since the system is empty, the compressor won't start when I try to do it. The switch can be by passed but I can't find the switch. The low side connector is in the middle of the line no where near the switch.

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Bob Lincoln

· #2 · 3 mo ago

PLEASE DO NOT USE A SEALER OR STOP LEAK OF ANY KIND.
If you have a leak, find the leak and fix it. Often it's just a metal gasket or O-ring not seated properly, or that connection not tightened enough. If it's an evaporator, condenser or hose, it will have to be replaced. Sealers WILL clog the system. That's how they work, they produce a clog. But you cannot control the location and extent of that clog, nor whether it will hold under pressure. So you can wipe out a system that could potentially have been repaired by proper means.
Draw a vacuum and put 1/2 can of freon that contains UV dye in, and then look for leaks with a UV penlight and protective goggles, and also listen carefully. Then fix the leak, draw the vacuum and recharge properly.

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ImperialCrown

· #3 · 3 mo ago

There is no low pressure switch. What manual are you using?
The 2010 JS uses an A/C pressure transducer in the high-side line. It can be read with a scan tool.
Find & fix the leak first.

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wheelsport

Discussion Starter · #4 · 3 mo ago

In order to put dye in the system, the compressor needs to turn on. I need to by pass the switch to allow it to turn on. In order to do that I need to find the switch. A lot of manufacturers place the switch near the evaporator or the low pressure inlet.. The evaporator on my car is under the radiator tank. I can't see a switch there. Where is it?

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Bob Lincoln

· #5 · 3 mo ago

wheelsport said:
In order to put dye in the system, the compressor needs to turn on. I need to by pass the switch to allow it to turn on. In order to do that I need to find the switch. A lot of manufacturers place the switch near the evaporator or the low pressure inlet.. The evaporator on my car is under the radiator tank. I can't see a switch there. Where is it?

You do not need to bypass the cutout switch. Just add enough freon with dye included to trip the compressor into turning on. It typically only takes about 1/2 can (6 oz) of freon.

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AllanC

· #6 · 3 mo ago

wheelsport said:
. . . .In order to put dye in the system, the compressor needs to turn on. I need to by pass the switch to allow it to turn on. In order to do that I need to find the switch. A lot of manufacturers place the switch near the evaporator or the low pressure inlet.. . . . .

Years ago Chrysler engineers put an A / C low pressure switch near or on the suction line outlet at the evaporator. Some had this binary (ON / OFF) switch attached to the expansion valve.

As ImperialCrown mentioned in post #4 there is no low / suction side A / C pressure cutoff switch. This vehicle uses a discharge side pressure transducer. It sends a varying voltage signal to the PCM / powertrain control module that indicates system pressure. An increase in refrigerant discharge pressure from the transducer signals the PCM to increase the pulse width of the signal sent to the wobble plate in the A / C compressor. The plate moves and increases the displacement output of the compressor and this gives more refrigerant flow and thus cooling at the evaporator.

The pressure transducer is not a binary switch. Using a jumper wire will not turn on the compressor. If the discharge side pressure transducer senses pressure in the system below 29 psi this signals the PCM to disable compressor operation.

As Bob L mentioned in post #5 and after pulling a vacuum on the system, connect container of R134a refrigerant to the system. Open the suction / low side valve on the manifold gauge set and let refrigerant flow into the system. You will not be able to empty the entire 12 oz container but should get pressure over 29 psi and the compressor will start to function.

Note that this vehicle uses a variable displacement compressor. There is no traditional clutch pulley. Anytime the engine is running the A / C compressor shaft is turning. You can tell the compressor is working as you should see a difference between the suction and discharge pressure. Hopefully you are using a manifold gauge set and monitoring both suction and discharge pressure.

. . . .The evaporator on my car is under the radiator tank. I can't see a switch there. Where is it? . . . .

Evaporator is located in the HVAC plenum box in the interior of the vehicle. It would not be under the radiator tank. The A / C condenser is located in front of the engine cooling system radiator and behind the grille.

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ImperialCrown

· #7 · 3 mo ago

The factory uses dye in their OEM A/C fill. If the refrigerant (PAG) oil has a greenish tinge to it, it probably has UV dye already in it.

Auto parts stores may also have a 'sniffer' for loan to find leaks.

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wheelsport

Discussion Starter · #8 · 3 mo ago

Thank you all for the help! I followed BobL's advise and added 1 can of R-134 before the copmpressor tripped. 39 degees of cold air

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Bob Lincoln

· #9 · 3 mo ago

Now try to track down the leak with a UV light and UV-protective eyeglasses, or a rented "sniffer" that detects refrigerant leaks. Sometimes you can find traces of oil residue if lucky.

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