1976 C20 AC Pressure Switch

[johnfl]

Hi there, I have a 1976 Chevy C20. Im about to completely restore my AC system as im doing a LS swap. I want to use the factory system so there is no LS computer controlling it.

Im a bit confused by the liquid line. I noticed there is a pressure switch on it. However, when i go to buy a new receiver drier there is a port on there which accommodate the pressure switch? I've also noticed square body trucks seem to have the pressure switch on the receiver drier (from photos im seeing online). Am i missing something? Where should i be mounting the pressure switch. From my research the current location seems to be the factory location.

Someone has disconnected the ac system in the past so its a bit of a mess. However, i know I will have to create new custom lines for my ls swap.

Thanks!

 

[Trucksareforwork]

The systems I’m familiar with only have a low pressure switch that shuts off the compressor when pressure drops too low on the suction side. It is normally on the receiver/dryer as you note. It mounts on a schrader valve.

I’m not familiar with your setup in the picture. Looks like a liquid side (high) pressure switch. Maybe someone else will come along and notice it.

 

[johnfl]

The systems I’m familiar with only have a low pressure switch that shuts off the compressor when pressure drops too low on the suction side. It is normally on the receiver/dryer as you note. It mounts on a schrader valve.

I’m not familiar with your setup in the picture. Looks like a liquid side (high) pressure switch. Maybe someone else will come along and notice it.

Thanks for the reply. I was assuming that switch that I have on my model is a high pressure switch. When I go to buy a switch through rock auto etc the switch is called a 'low pressure switch'.

Funny enough I was looking on youtube and right at 4:15 the gentleman has the same setup as mine.

xc_hide_links_from_guests_guests_error_hide_media

 

[75gmck25]

The stock setup on my ‘75 is a low pressure switch, and I don’t think they ever used a high pressure switch with R12, Freon. High pressure switch was often recommended for an R134a conversion, but I’m not sure it’s really needed. My A/C pressures with R134 are never higher than about mid to upper 200’s, and high pressure cutoffs are usually at 300.

 

[johnfl]

The stock setup on my ‘75 is a low pressure switch, and I don’t think they ever used a high pressure switch with R12, Freon. High pressure switch was often recommended for an R134a conversion, but I’m not sure it’s really needed. My A/C pressures with R134 are never higher than about mid to upper 200’s, and high pressure cutoffs are usually at 300.

Thanks for the reply. So I assume when i buy parts that i purchase a receiver dryer and connect the low pressure switch to that instead? Sorry for the questions. All the research I have done it seems that my model must have had a high pressure switch? I found this liquid line online and its to accommodate my truck. You can see it has the two ports on the line:

https://classicparts.com/1975-80-a-c-liquid-line?srsltid=AfmBOorZOxR8Hm5VEznGY5lzWKC06MF1v48guCD-DE3h93mMc3ip8tvk

Im confused!

 

[edgephoto]

Receiver dryers get installed in the high pressure side of the system. Accumulators are on the low side.

 

[Bextreme04]

Thanks for the reply. So I assume when i buy parts that i purchase a receiver dryer and connect the low pressure switch to that instead? Sorry for the questions. All the research I have done it seems that my model must have had a high pressure switch? I found this liquid line online and its to accommodate my truck. You can see it has the two ports on the line:

https://classicparts.com/1975-80-a-c-liquid-line?srsltid=AfmBOorZOxR8Hm5VEznGY5lzWKC06MF1v48guCD-DE3h93mMc3ip8tvk

Im confused!

The thing in your picture is a thermostatic cycling switch(freeze switch). It cycles the compressor off before the evaporator freezes up. It isn't actually ported onto the high pressure side at all I think.
Heres a pic from the same site.

You must be registered for see images attach

https://classicparts.com/chevy-gmc/...h-thermostatic-type#product.detail.attributes

 

[Trucksareforwork]

Receiver dryers get installed in the high pressure side of the system. Accumulators are on the low side.

Yep I used the wrong terminology. I am no ac tech and had just referred to the silver can as a receiver drier. It’s the ac accumulator! Low pressure side. And it’s where the low pressure switch usually is.

The OP looks to have a switch on the high pressure side. Putting a low pressure switch on the high pressure side is **** on a boar.

 

[Finkaire]

The low pressure cycling switch is located on the accumulator. The pressure switch shown is a high pressure cutoff switch. The switch with the capulator tube coming from it is the thermostat.

 

[johnfl]

The low pressure cycling switch is located on the accumulator. The pressure switch shown is a high pressure cutoff switch. The switch with the capulator tube coming from it is the thermostat.

I understand what your saying. My current accumulator (Original) does not have a low pressure switch though from factory from what i can see. It looks like the only switch that i can see is high pressure in the liquid line. Should the system have both a low and high pressure switch? Forgive my ignorance as im based in Australia so its not easy to look at someone else's setup.

 

[johnfl]

Yep I used the wrong terminology. I am no ac tech and had just referred to the silver can as a receiver drier. It’s the ac accumulator! Low pressure side. And it’s where the low pressure switch usually is.

The OP looks to have a switch on the high pressure side. Putting a low pressure switch on the high pressure side is **** on a boar.

I knew what you meant all along. I was calling it the r/dryer when the name should be the accumulator. I'm still confused if I'm meant to be running a low or high pressure switch. Both or just one switch?

 

[johnfl]

The thing in your picture is a thermostatic cycling switch(freeze switch). It cycles the compressor off before the evaporator freezes up. It isn't actually ported onto the high pressure side at all I think.
Heres a pic from the same site.

You must be registered for see images attach

https://classicparts.com/chevy-gmc/...h-thermostatic-type#product.detail.attributes

Thanks for the reply. I do understand that thermostatic switch is to stop the evaporator from freezing. If people dont have a high pressure switch then does this normally connect to the low pressure switch on other models? sorry if that question seems dumb. Just trying to learn here.

 

[Trucksareforwork]

I knew what you meant all along. I was calling it the r/dryer when the name should be the accumulator. I'm still confused if I'm meant to be running a low or high pressure switch. Both or just one switch?

If it’s the high pressure side, and you put a low pressure switch on it, then the switch will never really do anything. It’s made to open when pressure gets low.

I would think that’s a high pressure switch, meant to open when pressure gets too high. But again, I don’t recognize your setup. In any event you can jumper that switch if you are working on the compressor just to get it cycling.

 

[edgephoto]

Not trying to be the nomenclature police, just wanted you to know there is a difference. I know a/c very well but there are so many different ways to control the pressures and temperatures. If you have a service manual it should explain how the system works.

 

[johnfl]

If it’s the high pressure side, and you put a low pressure switch on it, then the switch will never really do anything. It’s made to open when pressure gets low.

I would think that’s a high pressure switch, meant to open when pressure gets too high. But again, I don’t recognize your setup. In any event you can jumper that switch if you are working on the compressor just to get it cycling.

Thanks, I do understand that I cant put a low pressure switch on the high pressure liquid line. As you inform it has to be a high pressure switch. Im a bit confused because when I go to buy a new accumulator it accommodates a port for the low pressure switch. Even when purchasing a new switch it specifically says 'low pressure'.

Not trying to be the nomenclature police, just wanted you to know there is a difference. I know a/c very well but there are so many different ways to control the pressures and temperatures. If you have a service manual it should explain how the system works.

I had a look through the service manual and unfortunately it mentions the pressure switch once but does not inform if its low or high. It also does not really go into much detail that i could find.