AC question

KO1960

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First time poster. This looks like a great site. My daughter has a 1990 GMC Sierra 1500 shortbed, with the 5.7. We have done quite a bit of maintenance and enjoy working on the truck together (I have a garage with lots of tools).

Our latest project is converting the AC to R134a. We purchased a kit from RockAuto which included a R4 compressor, a receiver dryer, condenser, o-rings and pag oil. The first problem encountered was the new condenser that came with the kit had different fittings, so the hoses wouldn't work. The old pressure switch at the back of the existing compressor disintegrated upon removal, so it has to be replaced. The liquid line that goes to the condenser galled up at the condenser and had to be cut out.

So, back to RockAuto. We ordered different hoses to fit the new condenser, an AC clutch switch (AC Delco 152832), which mounts on the receiver dryer, and a liquid line. RockAuto sells (2) different pressure switches for the back of the compressor, one for low pressure, and one for high pressure. They are both 2 wire switches, and the existing connector has only one pin.

Questions: 1. High pressure or low pressure switch? 2. The 2 wire connector - one wire to ground? 3. Anything else that we're missing?

Sorry for the long post. Thanks, Kurt.
 

PlayingWithTBI

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Did you forget the orifice tube that goes in the high pressure line from the condenser to the drier/receiver? Don't forget to flush the system too. If your 90 is the same as my 88 the pressure switch on the back of the compressor is for the fresh air door controlled by the HVAC module. If your HVAC doesn't have a "Max" cooling button then it's like mine.

Here's a thread I started about this system
https://www.gmt400.com/threads/how-does-the-ac-system-work-in-early-obs-models.45355/

Here's how I rewired the high pressure switch in series with the low pressure side
https://www.gmt400.com/threads/what-did-you-do-to-your-gmt400-today.4264/page-2329#post-1054401

HTH
 

KO1960

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Thanks for the reply. The existing orifice tube was installed on the liquid line at the condenser, so that's where we were going to install it on the new setup. Is this not correct? The white switch on the left looks like the old one; although, it was green in color. I had assumed that the compressor mounted switch and the one on the receiver dryer were refrigerant pressure related. I hadn't considered that it might control something else. We did do a good flush as well. I'll have to get back to you on the "Max" button. My daughter is going to send me a pic of the controls. Thanks for the links.

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PlayingWithTBI

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Thanks for the reply. The existing orifice tube was installed on the liquid line at the condenser, so that's where we were going to install it on the new setup. Is this not correct?
That's fine if that's where is was, mine is about 1/2 way between. I was just checking that you did change it since it wasn't mentioned in your OP.
 

KO1960

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Is the low pressure switch that you refer to the one on the receiver dryer? I couldn't tell from the picture.
 

KO1960

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Here’s the heat/ac controls. To duplicate your install, I need a switch with the pressure range you stated. I hate to ask PWT, but can you sketch a quick drawing showing the switches in series? I would appreciate it. Thanks.

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PlayingWithTBI

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I hate to ask PWT, but can you sketch a quick drawing showing the switches in series?
It took me a while, I had to watch the end of the race ending between the Bush brothers, hate em both, but at least a Chevy won! Then I had to refill my To-Kill-Ya drink and walk all the way out to my shop (30') to take a couple pics.

I figured it would be easier to show you how rather than firing up the CAD to generate a schematic...

I have the same HVAC controller you do (thought so)
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1st - you need to get this HP switch kit, you can get it anywhere, just make sure it's blue and comes with the 2-wire harness, green O-ring, and snap ring.
https://www.oreillyauto.com/detail/...4517359/1988/chevrolet/c1500-pickup-rwd?pos=1

2nd - Install it in the back of the compressor where the plug is (snap ring pliers)
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3rd - Cut the OE connector off the wire going to the original 1-wire switch connector and ground it to the T-Stat housing with all your other grounds.
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4th - Wire the new 2-wire HP Switch connector (I had red wire laying around) to the Low Pressure switch at your Drier/Receiver in series. Cut one of the wires, in this case I cut the light green one (makes no difference which), in 2 and splice the HP wires to those leads (I screwed in the pipe that goes from the Drier to the Evaporator to show the LP switch), make sense?
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KO1960

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Sweet! It does make sense now. I have ordered the switch you mentioned. The local parts houses didn't have any in stock. We'll probably get back to it in a couple of weeks, when my daughter isn't working overtime. The only difference that I can see with her truck and yours is the location low pressure switch. Hers is mounted on the receiver dryer itself. It's interesting, and sometimes frustrating, that GM made so many minor tweaks even in the same model year. It's certainly a learning curve. Thank you very much.
 
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