01 Explorer, carb converted, bypass the PCM with relay to POWER the AC system from interior control. AC now short cycling. Did I misunderstand?

[corerftech]

So you may have read in other posts here and there, I have converted an 01 Explorer, 5.0, with all whistles and bells still functioning, to carb and HEI.

When I mean all of it works, only THEFT is gone. I guess I used the most final method for eliminating PATS, LOL.

So my issue:

Today I completed the wiring for PCM bypass for AC operation.

The PCM received a 12v signal from the console switch to turn on A/C. The PCM the bussed the A/C cutoff switches together with the A/C power relay. Essentially the PCM is the remote control for the A/C system. Its gets to intervene at times when Ford wanted it to during your drive for a variety of reasons, none of which I care about.

So the bypass takes the 12v signal from the console switch, that 12v fires a relay I added. That relay is N.O. and when I turn the knob to A/C, it fires connecting the A/C master relay power to the A/C system. Then the pressure switches solely have control over cycling. Like OLD SCHOOL A/C.

I fired the A/C up today, short cycling constantly. Per the Helms manual, I see NOTHING in the circuit except pressure switches, to interrupt the system.

For more than an instant, I though, shit, I broke an AC line and over the last couple of months of work, I have leaked down! So I put gauges on the system (which I had rebuilt exceptionally well over a year ago) and it is full to the brim and quite happy!

Now the only thing I have changed since EFI removal is adding an Amazon 30A relay which replaces the PCM switching duty. I used the same versio of relay for my Overdrive column switch momentary conversion to low side switching, relay works phenomenally. I have not diagnosed ANYTHING at this time, not metered anything.

I wanted someone to validate the bypass method and my understanding of the PCM interaction with AC on/off control. I have added a few Helms excerpts for reference.

So Cir 361 is high current for lots of items- it drives the A/C system main relay coil. That coil applies power for the compressor clutch. VT wire cir 348 is 12v from the rotary control on the dash to turn AC on/off. 348 goes high, told the PCM to strap Cir 31 to 347. That completes the cutoff and cycle switch path so they can then control the compressor activity and regulate the system w or w/o a PCM.

I replaced the PCM with a relay, period.

Unless there is a bad relay, and there could be I guess, Ill check..... is there anything I am missing on the AC circuit???

I appreciaet your feedback and thank you in advance. I will report tonight re: relay testing.

 

[franklin2]

Find the low pressure switch, unplug the wiring connector and make a little jumper wire and jumper the terminals together in the wiring plug. If the compressor stops cycling, you know it's the switch.

If you find it's the switch, most of these switches are adjustable. If you are confident you have enough refrigerant in the system, look inbetween the terminals of the switch, a lot of them have a little screw in there. You can turn this screw to adjust the switch. Remember where you start from, and turn it a little bit and plug the connector back in. It will either not cycle as much(you went the correct way) or it hardly runs at all(you went the wrong way).

The only danger is if you adjust the switch too far, your evaporator will turn into a block of ice from too much cooling. If it's not very hot outside and or you have the switch on max and the cab is very cool, it will cycle the compressor.

P.S. If for some reason you do not have a lot of airflow over the evaporator coil, it will also tend to cycle. The evap coil does like to get clogged with dirt after years of use, and that will make it cycle.

 

[corerftech]

franklin2, I did just that when I walked outside after posting last. I put gauges on and ran the car. 35-40 and about 180 on high. I tested the relay system, it is launching with 14v available, no issues. Then I decide to bypass the LP switch with a jumper. Ran like a champ, blowing wicked hot air. Shut off and checked static pressure, even both sides at 105.

Needed batteries for the IR flashlight, went to store..... got home....... cant find a leak.

Then I laid down under the car and looked at bottom of my less than 1 year old Four Seasons compressor. A hand grenade had gone off with dye. Holy hell......

Weird that I get pressures consistent with a charge but ........ the fecal bomb that went off says something entirely different. Pissed, nothing that I mangled let go while doing the carb conversion. I disturbed the big line above radiator to clearance (bent the line midspan carefully) but its connection blok on the compressor is clean and free of dye. I figured that was my plac to leak if any...... nothing I distrubed leaked. The middle of the compressor took a huge dump (O-ring?)

Anyway--- thank you for the pointer to the LP switch.

Great part is---- the bypass relay works superb!

 

[franklin2]

180 sounds a little low to me. But it does depend on the ambient temperature as to what pressures you will see. If you trust the pressure switch and don't adjust it, and it's cycling more than usual and not blowing cold air, 99% of the time it's a little low on refrigerant.

If the low side drops below 30 when the compressor is running and then it suddenly cuts off, that is another sign it's a little low on refrigerant.

 

[corerftech]

Turns out the IR flashlight found the giant “exit wound” splatter of dye and oil on the bottom of the compressor. The midline o-ring has let go after I think 18 months on a new four seasons compressor.
Interestingly the gauges show what I mentioned prior but my gosh it created a psychedelic wonder. Would never have found it until I went under car and looked up.
I’ll try to reseal the compressor.