A/C low pressure switch
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Freshman User
Joined: Apr 2009
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From: Austin Texas
A/C low pressure switch
I am having A/C issues. I have replaced the A/C clutch and the High pressure switch then tried to fill with R134A and we could not get the low pressure above 30. The compressor would cycle off and on but the A/C clutch would not stay engaged. I want to replace the low pressure switch but I am not sure what the part number is. I need to pick one up at AutoZone so that part number would be helpful. I am trying to eliminate all problems before I take it to an A/C shop. I have all the gauges and equipment to fill the system just cant seem to get it working properly. Any extra advice would be helpful. Thanks and have a good day.
Lead Driver
Joined: Jun 2004
Posts: 6,317
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From: Amarillo, TEXAS!
You did evacuate the system to as close to 30 inches of vacuum as you could get it before adding refrigerant, right? If the compressor is cycling, the switch is at least working. It sounds like you didn't get enough refrigerant in it and it's still undercharged. How much refrigerant did you get in it (in ounces)? What are the low and high side pressures when the compressor cuts off and when it kicks back on?
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Freshman User
Joined: Apr 2009
Posts: 29
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From: Austin Texas
High side pressure was at 110 and the low side was getting to 30 and then when the clutch engaged it would drop to 25 or so. I never could get the low side to get above 30 and there was still plenty of 134 in the can.
Lead Driver
Joined: Jun 2004
Posts: 6,317
Likes: 583
From: Amarillo, TEXAS!
No disrespect intended, but you should really take it to an A/C shop and have them evacuate and recharge the system. MVAC systems aren't nearly as simple as the "A/C Pro" commercials on TV try to lead people to believe they are. Moisture and air in a refrigeration system can destroy it from the inside out, and cost you far more than it would have to just get it done right in the first place.
Posting Guru
Joined: Oct 2008
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1. Did you evacuate the system?
2. You can jump the low pressure safety switch with a wire to activate it to allow refrigerant to flow into the system. Also, heat a pot of water to 125*F and place the refrigerant bottle in that while charging the system.
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Freshman User
Joined: Apr 2009
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From: Austin Texas
I am not using A/C pro but you are right. I will just get it by the local A/C shop and get it looked at.
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2nd Gear
Joined: Apr 2024
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No high pressure reading on guages
Hey, I am currently having ac problems on my 93 f150
They compressor clutch is coming on for about 1-2 seconds (I'm assuming low refrigerant) so i tried adding some 134 and its reading about 50 psi on the low side but 0 psi on the high side. How much should the high side read and what could be causing it to not read any pressure
They compressor clutch is coming on for about 1-2 seconds (I'm assuming low refrigerant) so i tried adding some 134 and its reading about 50 psi on the low side but 0 psi on the high side. How much should the high side read and what could be causing it to not read any pressure
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Papa Smurf
Joined: Nov 2009
Posts: 1,080
Likes: 204
From: Woodstock, GA
On two different vehicles I spent a lot of time and $$$ to find out it was a simple little problem. The two wires to compressor from low pressure cut-off switch, wiggle the wires at switch when compressor stops. If compressor starts, then the wiring connector needs to be looked at.
I'd guess since I lay across engine when working on it, I screw up that connector, since I'm laying over it.
I'd guess since I lay across engine when working on it, I screw up that connector, since I'm laying over it.
Laughing Gas
Joined: Aug 2023
Posts: 971
Likes: 359
From: Glendale, AZ
Hey, I am currently having ac problems on my 93 f150
They compressor clutch is coming on for about 1-2 seconds (I'm assuming low refrigerant) so i tried adding some 134 and its reading about 50 psi on the low side but 0 psi on the high side. How much should the high side read and what could be causing it to not read any pressure
They compressor clutch is coming on for about 1-2 seconds (I'm assuming low refrigerant) so i tried adding some 134 and its reading about 50 psi on the low side but 0 psi on the high side. How much should the high side read and what could be causing it to not read any pressure
Laughing Gas
Joined: Jun 2013
Posts: 1,094
Likes: 514
From: Yokosuka Japan
i ended up paying to swap the condenser, the evap all of the lines and replacing most of the system as some jackass had pumped some kind of sealant into it to stop a leak and boyeee did it mess some things up.initially i swapped out the expansion valve and it was totally plugged, then got a little gas in it and it stopped taking gas again. finally took it to an ac repair shop and they had to pull 90% of the system due to the DA PO
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warren561
1987 - 1996 F150 & Larger F-Series Trucks
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Apr 2, 2013 04:31 PM
