Pressure switch necessary on a/c? - Chevelle Tech
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post #1 of 21 (permalink) Old Feb 6th, 20, 10:59 PM Thread Starter
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Brandon
 
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Pressure switch necessary on a/c?

So I'm in the process of replacing condenser, hoses, compressor, evap, txv, etc. Most of the parts are coming from original air. I'm running a factory poa and not delete.

One thing I noticed there is no pressure switch on the original air dryers but vintage air has them as an option. But the vintage air is male threads where the classic is female threads.

Is it necessary to even worry about a low/ high pressure switch?
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post #2 of 21 (permalink) Old Feb 6th, 20, 11:03 PM
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Re: Pressure switch necessary on a/c?

Yes, the low pressure switch prevents compressor burn up in the event of low refrigerant charge or stopped up dryer or inlet screen and the high pressure switch prevents damage to compressor, condenser, and high side lines in the event of pressure being too high.

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post #3 of 21 (permalink) Old Feb 7th, 20, 7:14 AM Thread Starter
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Re: Pressure switch necessary on a/c?

So I'm trying to figure out how to install one. I'm doing basically the original air stage 3 kit minus the poa delete.

Their r134a instructions even say one is recommended but I have yet to find how to do it on their site.

Vintage air sells a drier with a switch but they use male threads on the drier and classic uses female on theirs.

All I have found is the r12 port conversion t with the switch port. Is this my best option?

https://nostalgicac.com/oil-flush-re...port-7-16.html

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post #4 of 21 (permalink) Old Feb 7th, 20, 12:01 PM
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Re: Pressure switch necessary on a/c?

I can't believe that Classic or Vintage doesn't provide pressure cut of switches.
Quote:
This adapter will allow you to add a high low pressure switch and a R-134a high port to a stock R-12 system. The Tee fitting screws onto the factory R-12 high side port converting it to a charge port for R-134a. The adapter requires the removal of the stock valve core, the core can be removed with a valve core removal tool. The kit includes a new plug for the high low pressure switch with 18 inches of wire. The wire get spliced into the compressor coil wire.
The switch operates at the following pressures:
Low pressure cutoff 28 PSI
High pressure cutoff 398 PSI
High pressure on 312 PSI
There are two different ports on the factory R-12 discharge size. This adapter is for the larger size. If your vehicle uses the smaller port you will need part number 119-9905. If you are unsure which part you need use the cap off of the low side to test your vehicle. If the stock R-12 low side caps screws onto the high side this is the correct part. If the high side port is smaller then the low side you will need PN 119-9905.
This confuses me, are they saying that both high and low are included in the same switch and can be connected to the high side or the low side? Never heard of that before if that is what they are saying.

The high side cut off should be on the high side and the low side cut off should be on the low side so you would need two of the adapters.

I think I would talk to Classic air or Vintage air (or both)
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post #5 of 21 (permalink) Old Feb 7th, 20, 1:20 PM Thread Starter
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Brandon
 
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Re: Pressure switch necessary on a/c?

Ok, I was able to get this figured out.

They said because Im using the factory POA valve there are no ports I can attach the sensor too. They however had a inline adapter that screws onto the end of the hose.

https://www.originalair.com/ac-high-...tch-kit-o-ring

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post #6 of 21 (permalink) Old Feb 7th, 20, 2:26 PM
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Re: Pressure switch necessary on a/c?

Well, that's a new one on me (sensing low pressure on the high side) but it does make sense.

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post #7 of 21 (permalink) Old Feb 7th, 20, 2:41 PM
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Re: Pressure switch necessary on a/c?

Dean (or anyone else)


Didn't OEM A-6 compressors combined with POA valves utilize an overtemp switch on the back side of the compressor instead of a low pressure switch?
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post #8 of 21 (permalink) Old Feb 7th, 20, 2:46 PM
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Re: Pressure switch necessary on a/c?

Quote:
Originally Posted by dream66 View Post
Dean (or anyone else)


Didn't OEM A-6 compressors combined with POA valves utilize an overtemp switch on the back side of the compressor instead of a low pressure switch?
I believe that was a high pressure pop off

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post #9 of 21 (permalink) Old Feb 7th, 20, 5:39 PM
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Re: Pressure switch necessary on a/c?

HI
Blow out plugs
compressor and receiver driers can have them

Pressure switches
Can be used in 2 ways
1/ binary[high/low] can be used as a safety installed in the high side typically in receiver drier . This protects the system from complete failure and running no gas ie major leak low press. or condenser airflow blockage high press.
The alternate mounting is on a R12 service port

2/ the other type is where u have an orifice tube [no Tx valve ] The system can have a low press sw. on the suction/low pressure line /accumulator . Should have a seperate high side switch as well
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post #10 of 21 (permalink) Old Feb 7th, 20, 11:04 PM
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Re: Pressure switch necessary on a/c?

Quote:
Originally Posted by dream66 View Post
Dean (or anyone else)


Didn't OEM A-6 compressors combined with POA valves utilize an overtemp switch on the back side of the compressor instead of a low pressure switch?



If I recall, that is/was a superheat switch with accompanying fuse in the driver side inner fender
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post #11 of 21 (permalink) Old Feb 7th, 20, 11:41 PM
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Re: Pressure switch necessary on a/c?

Quote:
Originally Posted by LeoP View Post
If I recall, that is/was a superheat switch with accompanying fuse in the driver side inner fender
The fuse you are talking about was on later models but I don't remember the year. They were never on our Chevelles.

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post #12 of 21 (permalink) Old Feb 8th, 20, 2:09 AM
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Re: Pressure switch necessary on a/c?

Quote:
Originally Posted by LeoP View Post
If I recall, that is/was a superheat switch with accompanying fuse in the driver side inner fender
Quote:
Originally Posted by Dean View Post
The fuse you are talking about was on later models but I don't remember the year. They were never on our Chevelles.
1972 Chevelle and most other Chevys of that year.

72 A6 compressor had the superheat switch mounted on the backside and the thermal limiter switch was on the fender.
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post #13 of 21 (permalink) Old Feb 8th, 20, 2:25 AM
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Re: Pressure switch necessary on a/c?

That's what I have on my 72 Olds Cutlass
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post #14 of 21 (permalink) Old Feb 8th, 20, 11:07 AM
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Re: Pressure switch necessary on a/c?

My 68 that has a factory ac system does not have a pressure switch. Never did. The only protective switch in 68 was a low temp switch to shut down the compressor when it gets near to 32F ambient. It couldn't hurt to wire one in but 68 and probably earlier years didn't use them.
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post #15 of 21 (permalink) Old Feb 9th, 20, 1:33 AM
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Re: Pressure switch necessary on a/c?

hi
In various GM cars with an orifice tube and accumulator , the super heat switch is a pressure switch senses ultra low pressures when the evaporator is full of cold low pressure liquid and sending excess liquid back to the compressor . The design is a safety aspect for the compressor . If the system is working properly the safety switch should not be used .

In the 90`s even some GM cars were retrofitted with such devices .

Biggest issue with those is some factory accumulator / POA / orifice type aircons were designed really badly by GM ..
Although not every model .

A thermal switch is an overheating compressor disconnect and /or operates a warning light/ac light flashes . GM pls many other brands use this idea
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