The best electric fan install with a trinary switch

[1998_K1500_Sub]

Here's a comment about another means of controlling an electric fan.

As I think is well known, my 1998 Suburban and I suspect all 1996 and later, the high-pressure switch (~450 PSI, from memory) near the high-side service port has two functions AFAIK when activated (both described in the GM service manual):

- the ECU forces the system into recirc mode, and

- If equipped with the aux cooling fan on the condenser / radiator, the ECU turns the fan on.

These operations can be demonstrated by removing the switch's connector and shorting the terminals with a jumper.

By replacing that high-pressure switch with one which operates at a lower pressure (e.g., 180-220 PSI), the aux cooling fan can effectively be turned on when the AC compressor engages. This isn't a bad option if one doesn't object to the forced engaging of recirc which would also occur.

Methods for enabling ECU control of an aux fan, if not already present on the vehicle, are known.

Others might have better ideas, as well. I like what you've done but I would like to avoid the plumbing changes.

 

[kylenautique]

While I really like what you're trying to do in this fan retrofit, this step sounds troublesome.

It's known that PAG and liquid R134a are miscible.

Allowing the system to blow-down after removing the service port, even for a brief while, is going to carry some oil out of the system... more, if liquid R134 finds its way to the opening, because of the oil miscibility. Replenishing that oil is a guessing game since there's no reliable way (IMHO) to determine how much may have been blown out.

Too, any R134 exiting the port during this "fitting remove / replace" operation could be a frostbite concern if one's hands / eyes / face aren't protected, particularly if liquid R134 were present.

I don't want to be a Chicken Little but... I don't think this is a good idea.

If I had to do the same thing, I would probably take the truck to an AC shop, have them evacuate the system and then backfill with shot of R134a to bring the system pressure to 0 PSI or maybe a few PSI above zero, then swap the fittings under zero or very low pressure, and *then* recharge the system. It's more money but it eliminates the concerns I noted earlier.

I totally appreciate the concern. When I did this, I decided after the fact to recharge my system. I have all the tools to do it properly. I have lots of experience retrofitting a/c units on older rigs, so Its not my first rodeo. Expanding on why I went this route for the setup is this… You could buy a new hose and weld in a port for the trinary switch. Only downside if you ever have to replace it, you have to have the port welded on again. This setup keeps everything OEM replaceable. Vintage air sells the weldable port, so if anyone wants to do this and not modify the service port, all you need to do is weld a port onto the high pressure hose for the trinary switch.

I’ve been running this setup since July and I drive my truck a TON. No issues.

 

[kylenautique]

Here's a comment about another means of controlling an electric fan.

As I think is well known, my 1998 Suburban and I suspect all 1996 and later, the high-pressure switch (~450 PSI, from memory) near the high-side service port has two functions AFAIK when activated (both described in the GM service manual):

- the ECU forces the system into recirc mode, and

- If equipped with the aux cooling fan on the condenser / radiator, the ECU turns the fan on.

These operations can be demonstrated by removing the switch's connector and shorting the terminals with a jumper.

By replacing that high-pressure switch with one which operates at a lower pressure (e.g., 180-220 PSI), the aux cooling fan can effectively be turned on when the AC compressor engages. This isn't a bad option if one doesn't object to the forced engaging of recirc which would also occur.

Methods for enabling ECU control of an aux fan, if not already present on the vehicle, are known.

Others might have better ideas, as well. I like what you've done but I would like to avoid the plumbing changes.

Here is the issue with this. The ecm can control the fans for engine temp. You can use the compressor to trigger the fans. Only problem is that every time the compressor kicks on, the fans will kick on and that is a large shock on the power system Which will make your lights dim for a brief moment. My way uses pressure only as a trigger. I tried adapting the trinary switch into the high pressure port, but I was not able to find a good way to adapt it. You could weld on a port on the high pressure side line for the trinary switch, but that makes your hose unique and not easily replaceable for the system to work. Doing this mod is really no different than converting a older rig from R12 to R134.

 

[kylenautique]

The 0411 ecm has pressure controls for fan control with a/c. The black box ecm only controls engine temp fan control. I don’t have a 0411 ECM so I didn’t look very hard into this. You might be able to control the a/c fan control with the 0411. If anyone has information to add on this, I’d be interested to hear. With a stock black box ecm, you really need a trinary switch to run the A/c fan control properly.

 

[mattillac]

Speaking of ac pressure, when using the PCM cooling fan option (to run main cooling fans) in a 98 and newer (mine is 99), why not rely on the ac pressure switches already in place and the default PCM ac settings ?

The descriptions make it seem as though the PCM would command the cooling fan ON somewhere between 300-360 psi and OFF at 250. The ac system would supposedly be protected by the high pressure cutoff switch which activates somewhere between 410-450 psi.

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Like, are those pressures to high for safe and/or efficient ac operation ?

 

[351FUN]

Unfortunately this only works for those of us that have A/C, I did mine a bit different and it is an independently wired setup.

It's unnecessary for us without AC, as there isn't a compressor draw at the same time the fans kick in.