Run AC with a toggle switch?

[1998_K1500_Sub]

The high side pressure switch needs to be there in hot weather with a heat soaked interior. When the inside of the vehicle is starting out over 120°F and sometimes as much as 150°F, it drives the head pressure stupid high even with the windows down.

The high underhood heat soak is a related, additional factor when starting out.

Related but slightly different topic: The 1995 S-series pickups and Blazers (and possibly other years) have a delay that prevents the AC compressor from engaging for (from memory) 15s after engine start. Keep in mind, the 1995 used an R4 compressor and R134a, which I think was only done for a few years 1992(?)-1995. I have always wondered why GM went to the bother of adding the delay. Today, now, I think I finally have a clue: They may have had a heat soak issue on that series (think: AZ temps) and so included that delay to give the engine fan some time to pull air through the condenser and engine bay and cool things down a bit before engaging the compressor, in particular so that the R4 didn't suffer the extreme high-side pressures. I know I've read, someplace, that the R4 "didn't like" high pressures... maybe its sealing problems were exacerbated under such conditions. I'll add that the 1995 K1500's (one of which my father owned), R4 w/ 134a, did not have this delay.

Another different topic: I used that Sanden #4261 on my Suburban, instead of the "spec'd" Sanden #4440, simply because it had the smaller pulley (112mm, 4.41") than the #4440 (130mm, 5.12"). I wanted the increased pumping volume / engine RPM that it provided at low RPM driving. Consequently, with the 8" diameter crank pulley, I tuned the ECU AC disable to 3000 engine RPM (a little low, but I never drive long with the engine over 3000RPM anyway).

@L31MaxExpress, Sanden's site says the #4261 pulley is 112mm - 4.41". I made a mistake in my earlier post in this thread about the #4440 pulley diameter; I'll go back and add a note to it with a correction.

 

[L31MaxExpress]

The high underhood heat soak is a related, additional factor when starting out.

Related but slightly different topic: The 1995 S-series pickups and Blazers (and possibly other years) have a delay that prevents the AC compressor from engaging for (from memory) 15s after engine start. Keep in mind, the 1995 used an R4 compressor and R134a, which I think was only done for a few years 1992(?)-1995. I have always wondered why GM went to the bother of adding the delay. Today, now, I think I finally have a clue: They may have had a heat soak issue on that series (think: AZ temps) and so included that delay to give the engine fan some time to pull air through the condenser and engine bay and cool things down a bit before engaging the compressor, in particular so that the R4 didn't suffer the extreme high-side pressures. I know I've read, someplace, that the R4 "didn't like" high pressures... maybe its sealing problems were exacerbated under such conditions. I'll add that the 1995 K1500's (one of which my father owned), R4 w/ 134a, did not have this delay.

Another different topic: I used that Sanden #4261 on my Suburban, instead of the "spec'd" Sanden #4440, simply because it had the smaller pulley (112mm, 4.41") than the #4440 (130mm, 5.12"). I wanted the increased pumping volume / engine RPM that it provided at low RPM driving. Consequently, with the 8" diameter crank pulley, I tuned the ECU AC disable to 3000 engine RPM (a little low, but I never drive long with the engine over 3000RPM anyway).

@L31MaxExpress, Sanden's site says the #4261 pulley is 112mm - 4.41". I made a mistake in my earlier post in this thread about the #4440 pulley diameter; I'll go back and add a note to it with a correction.

You are correct on the pulley. I just used your math and rolled with it. Mine is still set at 4,500 crank.

 

[letitsnow]

Well - this is the first step to eventually getting the AC installed/working on my k2500 with a toggle switch...

I am learning how to check temps and charge my s10 with these.

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When I first hooked these up, I had about 25 psi on the low side/100 on the high. The ac worked, but wasn't super cool. After making a couple of rookie mistakes, I got the s10 charged to 30/200psi. The air was cold. I unhooked everything, and the high side schrader valve was leaking. I took a magnifying glass and looked at the valve closely, seeing where it unscrewed, ran to autozone and got a replacement for $11. Recharged (as all of my first charge had leaked out of course) up to 33/215 this time. All good. Now to see if it holds a charge....

I learned quite a bit today. The low side switch made the compressor cycle at 46/22. It only did that until I put more juice in, but it was neat to watch it function. I never got the psi high enough to watch the high side switch function - chickened out.

 

[L31MaxExpress]

Well - this is the first step to eventually getting the AC installed/working on my k2500 with a toggle switch...

I am learning how to check temps and charge my s10 with these.

You must be registered for see images attach

When I first hooked these up, I had about 25 psi on the low side/100 on the high. The ac worked, but wasn't super cool. After making a couple of rookie mistakes, I got the s10 charged to 30/200psi. The air was cold. I unhooked everything, and the high side schrader valve was leaking. I took a magnifying glass and looked at the valve closely, seeing where it unscrewed, ran to autozone and got a replacement for $11. Recharged (as all of my first charge had leaked out of course) up to 33/215 this time. All good. Now to see if it holds a charge....

I learned quite a bit today. The low side switch made the compressor cycle at 46/22. It only did that until I put more juice in, but it was neat to watch it function. I never got the psi high enough to watch the high side switch function - chickened out.

Sounds about right for a single evaporator. Mine runs a bit higher on the pressure but it is a dual evaporator system charged with R152a and it was 102°F at the time. At idle, got it down to 41°F in the left vent, 38°F in the center vent and the rear was about 40°F. After 10 minutes it was extremely cool inside.

Once you are driving down the road with good airflow across the condenser the compressor will cycle on that 22 psi cutoff.

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[1998_K1500_Sub]

I learned quite a bit today.

Congratulations!

The low side switch made the compressor cycle at 46/22.

Sounds typical.

I never got the psi high enough to watch the high side switch function - chickened out.

If you want to see that high-side switch operate, just put a piece of cardboard (e.g., from a case of pop... thin and flexible) in front of the condenser while the AC is on / compressor running. The high-side pressures will jump immediately. If they get to 500psi without some sort of response, e.g., compressor shut-off, don't persist; remove the cardboard and let the pressures drop.

 

[letitsnow]

If you want to see that high-side switch operate, just put a piece of cardboard (e.g., from a case of pop... thin and flexible) in front of the condenser while the AC is on / compressor running. The high-side pressures will jump immediately. If they get to 500psi without some sort of response, e.g., compressor shut-off, don't persist; remove the cardboard and let the pressures drop.

Thanks.

I'll pass (for now) on the cardboard test. Anything with 500 psi on a truck this old scares me!

 

[1998_K1500_Sub]

Thanks.

I'll pass (for now) on the cardboard test. Anything with 500 psi on a truck this old scares me!

Yeah, I don't blame you But at least "now you know".

I did it once on a Toyota because I needed to check the HP switch operation.

You might want to get yourself a refrigerant scale. Charging by weight let's know how much refrigerant you actually have in the system (which you likely know, but...). I found mine on eBay.

 

[letitsnow]

My s10 AC has been working great. I am now more confident that I can make AC work in my k2500, so I ordered parts from rock auto. I was going to wait until this coming winter to order, but with people talking about the excessive heat and climate change, I worry that these part prices will rise soon.

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[letitsnow]

Today I installed everything. All went well. I ran a power wire through a 10 amp fuse, then to the toggle switch, from there to the green wire on the compressor. I then ran wire from the black wire on the compressor to the high pressure switch, then from there to the low pressure switch, then from there to ground on the firewall.

I put in 32 ounces of r134a and I now have A/C!

I will have to use it for a while before I consider this a success. I expect there to be some teething problems.

A couple of observations:

1. I bought both pressure switches and one line as "genuine gm". One had a made in china sticker, one a made in mexico, the other a made in taiwan sticker.

2. This sticker was on the compressor wrapper.

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[L31MaxExpress]

Today I installed everything. All went well. I ran a power wire through a 10 amp fuse, then to the toggle switch, from there to the green wire on the compressor. I then ran wire from the black wire on the compressor to the high pressure switch, then from there to the low pressure switch, then from there to ground on the firewall.

I put in 32 ounces of r134a and I now have A/C!

I will have to use it for a while before I consider this a success. I expect there to be some teething problems.

A couple of observations:

1. I bought both pressure switches and one line as "genuine gm". One had a made in china sticker, one a made in mexico, the other a made in taiwan sticker.

2. This sticker was on the compressor wrapper.

You must be registered for see images attach

Glad you added some switches. Hopefully ends up working reliably for you.