Mechanics

A/C ACCUMULATOR LOW PRESSURE SWITCH

Chevrolet Silverado

1994 V-6 silverado 300,000 miles. 134a
Airconditioning has 50 psi on low side with compressor running and accumulator low pressure switch jumpered out. When switch is connected to accumulator compressor will not run. 12 volts to switch and nothing out. Can the low pressure switch be bad, changed out without pumping down system as noted in this forum? What pressure does the switch open and close at?
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Olddrum1
August 4, 2007.




I am not positive but I am pretty sure that there is a shraeder valve behing the low press switch. The switch just screws onto it, but to be sure stop by a parts store and have them check and see if they have a new accumulator on the shelf. If so ask them to pull and open the box and see if it has a shraider valve installed. If they one at the parts store doesn't have one then you will have to have the system evacuated before changing it out. Good luck.

Gary
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Tiny
Garfield
Aug 4, 2007.
94 Cheverolet Silverado V6 300,000 mile 134a
Does anyone know what the cut out and cut in pressures are for the low pressure switch on the accumulator of a 94 silverado are? What Pressure should one run the freon on low and high side of this vehicle with 134a?

Tiny
Olddrum1
Aug 6, 2007.
I would use the original settings as far as pressure. It will differ depending on the outside temp in front of the condensor. Basically as the temp goes up so will the pressure. Generally a fullly charge ac will have around 70 psi in the system when the ac is off. The suction you are looking at around 35-45 and discharge is going to differ with outside temp, look around 185 psi but it can go a little higher on a hot day but I would not let it get about 200 with the car idling. When you fill the system it will help if you have access to a large fan to put in front of the car while charging. It will lower the temp at the condenser which will help the system take the freon. If you are switching to 134 from 12 and your vehicle doesn't have an extra electric fan installed already I would suggest that you get one. IT will dramatically help they system work better.

Tiny
Garfield
Aug 6, 2007.
The pressures you supplied, are they for R12? R134a has a higher boiling point if I am not mistaken and not as efficient as R12, which would give it slightly higher operating pressure than the R12. I am probably wrong on this, I just did not want to over charge system and slug the compressor with liquid.

Tiny
Olddrum1
Aug 7, 2007.
You are right r-134 does have a higher pressure but the pressures stated should get you in the ballpark. Also remember that you will only need about 70-75% as much 134 as you did R-12. I converted my 91 civic to R-134 about 2 yrs ago. I bought a air vacuum pump from harbor freight for about 20 dollars. It did a good job but I did vacuum the system down for about 5 hours(Honda repair manual recommended doing it for about 12 hours). After I put the system together I left the old dryer(accumulator in your case) while I vacuumed the system down for about 1 hour then closed off my manifold set and left it for 45 minutes to make sure the system was tight and holding a good vacuum. After that I changed the accumulator out and put the new one on and then vacuumed the system for 5 hours more. The vacuum pump will get rid of the air fast but it takes a while to get all the moisture out of the system because it has to flash(convert the moisture into a gas) the moisture into a gas to get it out. Then I put in Artic Freeze R-134A avail at Advance auto parts. Now the system cools down to around 38-42 degrees.

Tiny
Garfield
Aug 7, 2007.

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