Author Topic: Discharge pressure cutout switch  (Read 2493 times)

Offline runnergeorge

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Discharge pressure cutout switch
« on: July 16, 2020, 09:46:18 PM »
Hey everyone! I got a 75 Cheyenne 350 that I’m installing new AC into from classic auto air. The kit I bought did not come with a new discharge pressure cutout switch so I sourced one from my local auto parts store but when I went to screw it onto the fitting on the accumulator I found out it does not fit! It happens to be too small, I’m thinking it is meant for R12 and not R134? Does anyone have any insights about this, or maybe a place where I can find a switch that fits larger fittings? Thanks guys and gals!

Offline JohnnyPopper

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Re: Discharge pressure cutout switch
« Reply #1 on: July 16, 2020, 09:57:13 PM »
Best bet is to contact classic auto air and ask them why they didn't supply one or advise you on the need to get one that works. Along with a viable part number.

They all work the same, doesn't depend on R12 or R134. When you lose pressure, it keeps the compressor from engaging.
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline VileZambonie

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Re: Discharge pressure cutout switch
« Reply #2 on: July 17, 2020, 10:51:07 AM »
The accumulator is on the suction side i.e. low pressure switch.
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline runnergeorge

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Re: Discharge pressure cutout switch
« Reply #3 on: July 17, 2020, 03:08:01 PM »
Shoot I was hoping just any low pressure switch would work as long as it says it fits my vehicle. Sadly mistaken!

Offline runnergeorge

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Re: Discharge pressure cutout switch
« Reply #4 on: July 17, 2020, 03:29:55 PM »
Update. I spoke with a tech at Original Auto Air and they said that 75 was tricky because depending on where the truck was made it could have a cycling switch attached to the accumulator or a discharge cutout switch. According to the wiring diagrams from this forum my truck came with a pressure cutout switch. Does anyone on here know or can point me in the right direction!? Help!

Offline VileZambonie

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Re: Discharge pressure cutout switch
« Reply #5 on: July 17, 2020, 03:56:30 PM »
It's a low pressure switch that you need so they sold you an aftermarket system with no low pressure switch? That makes little sense. Are you using the factory acuumulator or an aftermarket one? Are you sure you didn't get a receiver drier with your kit? that would be on the high side in the liquid line. Can you post a link to what you bought? Was your truck factory AC equipped?
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                         /  _ _ _\_
              ⌠¯¯¯¯¯'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline JohnnyPopper

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Re: Discharge pressure cutout switch
« Reply #6 on: July 18, 2020, 01:27:56 PM »
Heads up on buying from 'classic air'

Or as bd would say; caveat emptor
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline runnergeorge

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Re: Discharge pressure cutout switch
« Reply #7 on: July 18, 2020, 04:51:31 PM »
Here is the link. https://www.originalair.com/73-76-chevrolet-gmc-c-k-series-truck-134a-rotary-compressor-upgrade-kit-stage-1

My guess for the kit is it’s designed to be an “upgrade” and to use some components already in the engine compartment. And me being new to the game when it comes to older trucks didn’t know I was missing some other pieces. My truck is factory AC equipped. And according to the website the kit I ordered comes with a new accumulator not a receiver drier.

Offline VileZambonie

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Re: Discharge pressure cutout switch
« Reply #8 on: July 19, 2020, 09:49:39 AM »
So it's basically a sanden 508 compressor kit. You can use the factory low pressure switch mounted to the accumulator. If the one you got doesn't fit, try a later model year low pressure switch, like for a 1984.
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              ⌠¯¯¯¯¯'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline MIKE S

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Re: Discharge pressure cutout switch
« Reply #9 on: July 19, 2020, 02:05:09 PM »
Try a Murray 36496 or equivalent. It is an accumulator mounted cycle switch for a 1995 G van. It is adjustable and has an M12x1.50 thread.

Offline runnergeorge

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Re: Discharge pressure cutout switch
« Reply #10 on: July 19, 2020, 11:45:00 PM »
Unfortunately my truck didn’t have the factory switch installed, just the connector that goes from the switch to the temp switch in the air box and the compressor. I decided to order a cycle switch from original auto air after speaking with one of their techs. If it’s doesn’t work then I will be looking for a low pressure switch! Other note, does it matter which terminal the switch is plugged into the temperature switch?

Offline VileZambonie

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Re: Discharge pressure cutout switch
« Reply #11 on: July 20, 2020, 07:13:13 AM »
Ahh you have an early model, which you did say, sorry about the misinformation since it doesn't apply to your truck and I don't know why I didn't pick up on that in the first place. Heat stroke or too much beer or both. So if you are using the original controls and wiring, you have a temperature switch with a sensing bulb in the Evaporator. Make sure this is clean, connected and functioning or the compressor will not turn on. The compressor discharge pressure switch also stops the compressor from running if the pressure is outside of parameters. Try part # 4-Seasons 35757. I'll try to snap some pics since I have some in tact systems.
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                         /  _ _ _\_
              ⌠¯¯¯¯¯'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline VileZambonie

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Re: Discharge pressure cutout switch
« Reply #12 on: July 20, 2020, 07:29:20 AM »




,                           ___ 
                         /  _ _ _\_
              ⌠¯¯¯¯¯'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline MIKE S

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Re: Discharge pressure cutout switch
« Reply #13 on: July 20, 2020, 08:44:08 AM »
I never liked the performance of the thermostat sensing type systems. They seemed to keep the compressor off to long while cycling causing warmer than desirable temperature especially if the system was slightly low on refrigerant. I would change those to a cycle switch system by adding the switch to the accumulator and connecting the wires from thermostat to the cycle switch. They are easily adjustable to the 134 pressures for maximum cooling. I would probably just jump the wires to the high pressure cutoff switch as the later model systems had the same components  without the switch. Unless you have little to no airflow thru the condenser you shouldn’t have a problem. 

Offline runnergeorge

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Re: Discharge pressure cutout switch
« Reply #14 on: August 05, 2020, 02:00:45 PM »
Thank you for the great information! After speaking with an AC tech in my area they determined that it is a cycling switch and luckily they had one! The tech also installed all the hoses and charged the system. Unfortunately, since they did the work which was completed today, my blower motor isn’t coming on like it was when I dropped it off. I’m hoping it’s a blown fuse but I’ll find out when I pick it up. I know this may not be the correct threat for this question, but does anyone have an idea of why the blower motor may not work with everything hooked up?

I’ve replaced the relay, the fan selector switch, and the compressor is new. I also replaced the wire that goes from the compressor to the cycling switch. Maybe I need a to temp switch for the evap core?