Ac issues

[87GrandMarq]

I have 2 16’’ fans I’ll be mounting. There is a bracket that is in the center but it doesn’t interfere with the larger fans. I’ve already mocked one up the last time I messed with the ac.

It would be nice to have the ecu control them but I think I’m going to install them with a relay triggered by the ac clutch. I’m thinking I’ll need a 3g swap at the same time so I’ll need to get some things for that too.


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[87gtVIC]

but I think I’m going to install them with a relay triggered by the ac clutch.

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This is what I have in mind if I end up doing this.

[sly]

It would be nice to have the ecu control them but I think I’m going to install them with a relay triggered by the ac clutch.

This is what I was planning on and the electric fan I replaced the mechanical fan with would be using the PCM. Aux fans on AC clutch. I would tap the line before the low side pressure sensor so if I wanted to use AC ON as a fan trigger on a track day or something, I could just pull the connector off the low side sensor.

[87gtVIC]

This is what I was planning on and the electric fan I replaced the mechanical fan with would be using the PCM. Aux fans on AC clutch. I would tap the line before the low side pressure sensor so if I wanted to use AC ON as a fan trigger on a track day or something, I could just pull the connector off the low side sensor.

Noted.

[gadget73]

if the PCM has fan control capability I'd use that honestly. It should turn the fans on with the AC since there is an input from the AC compressor trigger to the PCM.

Failing that, a 2 speed setup that uses a resistor is easier to deal with, especially if you add a time delay in there so it starts on low first. Much less inrush current if it starts through the resistor and runs for say 2 seconds before bypassing the resistor for full speed. Less likely to roast relays doing it that way.

[sly]

Failing that, a 2 speed setup that uses a resistor is easier to deal with, especially if you add a time delay in there so it starts on low first. Much less inrush current if it starts through the resistor and runs for say 2 seconds before bypassing the resistor for full speed. Less likely to roast relays doing it that way.

This is the way mine is set up now. High trigger goes through a low first delay circuit I built myself with a 555 timer. Using the whale relays. Works well, but I have no control over adjusting temperature switching. The AC trigger goes to the low speed relay only. Would simplify a lot of wiring to just wire that mess up to the PCM. I would have to switch to common power instead of common ground on the relay coils though. My setup is high side switched while the PCM uses low side switching.

[Kodachrome Wolf]

I have 2 16’’ fans I’ll be mounting. There is a bracket that is in the center but it doesn’t interfere with the larger fans. I’ve already mocked one up the last time I messed with the ac.

It would be nice to have the ecu control them but I think I’m going to install them with a relay triggered by the ac clutch. I’m thinking I’ll need a 3g swap at the same time so I’ll need to get some things for that too.


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FWIW, I used the low pressure switch feed wire to trigger a relay to kick on my fan whenever I use the A/C. One wire is hot whenever you put the lever in an A/C mode, and it shuts off when it’s in any selection that doesn’t require it. I’d not recommend the A/C clutch wires as a trigger since it cycles.

[87GrandMarq]

But the compressor is on in every mode except vent anyway. I guess having it triggered that way could put a strain on things because it would be cooling the condensor which would be cycling the clutch (which is always on right now) which would probably not be good for the relay. I guess since it cools fine while driving just put a switch on it to use while idling. Eventually have it to where it’s triggered by a temp probe set to keep the condensor under a certain temp. Hmm decisions, decisions.


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[sly]

you only need to trigger the aux fans when the compressor is on, which makes that the easiest way to trigger them and if you take the signal from before the low pressure switch, it will be on at all times the system is requesting the compressor to run and not just while the compressor is running. This actually puts less strain on the relays and fans as there is less start/stop cycles. Using a temperature probe obviously will work as well, but may increase cycling of the fan depending on the set temp. Temperature monitoring is more important with the radiator. The condenser needs pressure monitoring. There's no danger in running the switched setup for the condenser, but a laggy temp sensor may allow it to get to too high of a pressure if there's no air flow. This isn't an issue with a mechanical fan as there's almost always good airflow. It's really just to augment what's currently there anyhow to get better cooling on those extra hot days so adding a "low temp cut out" to the relay control to the aux fan would probably be the best bet. On hot days, that would always be on, but on cold days, there's no need for the aux fans to run.

[87GrandMarq]

So then my original idea would be ok?


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[sly]

Yeah.

[87GrandMarq]

When screwing around with my radio earlier today I noticed the compressor was cycling, which it never does. The ambient temps were lower than before so I thought maybe that’s what it was but then the temp climbed after 10 minutes or so. I got out and watched the compressor cycle, which it stopped cycling and stayed on, and noticed that the lines to the evaporator were frozen. So it was a matter of adjusting the pressure switch. I tightened it slightly twice and it stopped freezing and stayed below 50* while idling so I took it for a short spin then let it sit and idle since that’s when it likes to warm up. It stayed in the low 40’s. I need to wait for a hot day and drive it all day to really test it but it appears that I may have found the culprit. Perhaps it’s been freezing this whole time. I guess I’ll know hopefully soon. I’d like to start dailying it again to keep all the miles off my P71 and Mustang.




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[gadget73]

sounds like the low side pressure cutout was too low if there was that much ice on the line. The lower the pressure, the colder it gets. The big risk of overly cold evaporators is the water stops draining and turns into ice. Once that happens you get no airflow through it, so the temperature goes up. The other big problem is that if liquid gets back into the compressor it will be destroyed. Liquid does not compress. R134a cutout should be in the 20-25 psi range. Too low and it freezes, too high and it just doesn't get cold. R12 was in the 25-30 range.

[87GrandMarq]

I wonder if it was set too high out of the box then when you told me to adjust it I went too low. I’ll update this once I start driving this one again.


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[gadget73]

possible, or it was at the right pressure but flaky until it was adjusted. I've had these switches not function properly before.