AC compressor work on 1&2 not not 3&4?
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Joined: Oct 2018
Posts: 63
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From: Arlington, tx
AC compressor work on 1&2 not not 3&4?
I have read about the the PFC ground relay mod, and the diode mod from the CCU harness.
But I'm still a bit unclear, about which mod to go with, have anyone encounter this issue before?
Car: 1994 Fd, Blitz FMIC, Power FC, recently convert from R12 to R134a. nothing extreme.
Problem details: Just had R134a converted from R12. AC work perfect, outlet temp is roughly 37F on speed 1&2. But it does have a constant hissing noise from inside the car.
However my mechanic shop told me something is weird because the AC compressor on work on speed 1&2, when you turn it over to 3 the AC compressor cut off.
Speed 1: compressor on, AC led light on, blower on speed 1 (Blow cold)
Speed 2: compressor on, AC led light on, blower on speed 2 (Blow cold)
Speed 3: compressor OFF, AC led light on, blower on speed 3 (Blow regular temp)
Speed 4: compressor OFF, AC led light on, blower on speed 4 (Blow regular temp)
On my way home, I stop by the gas station. With the car off for approximately 5 minutes. During my drive home I noticed, the AC was not cold...
So I pull over to a side street, to mess around with the AC button, and the AC speed ****.. seem like the AC compressor was kick on or off.
Burst out with frustration.. I decide to turn off the car and turn it back on.. and bamm AC work again this time on all 4 spd..
Currently I'm guessing there got to be some short of electric issue dealing with the Power FC.
Could anyone share any thoughts?
But I'm still a bit unclear, about which mod to go with, have anyone encounter this issue before?
Car: 1994 Fd, Blitz FMIC, Power FC, recently convert from R12 to R134a. nothing extreme.
Problem details: Just had R134a converted from R12. AC work perfect, outlet temp is roughly 37F on speed 1&2. But it does have a constant hissing noise from inside the car.
However my mechanic shop told me something is weird because the AC compressor on work on speed 1&2, when you turn it over to 3 the AC compressor cut off.
Speed 1: compressor on, AC led light on, blower on speed 1 (Blow cold)
Speed 2: compressor on, AC led light on, blower on speed 2 (Blow cold)
Speed 3: compressor OFF, AC led light on, blower on speed 3 (Blow regular temp)
Speed 4: compressor OFF, AC led light on, blower on speed 4 (Blow regular temp)
On my way home, I stop by the gas station. With the car off for approximately 5 minutes. During my drive home I noticed, the AC was not cold...
So I pull over to a side street, to mess around with the AC button, and the AC speed ****.. seem like the AC compressor was kick on or off.
Burst out with frustration.. I decide to turn off the car and turn it back on.. and bamm AC work again this time on all 4 spd..
Currently I'm guessing there got to be some short of electric issue dealing with the Power FC.
Could anyone share any thoughts?
The root cause is probably bad contacts on the fan speed switch. The PFC is more sensitive to the poor connection than the stock ECU for some reason. The relay mod is a work around. From what I can tell that mod takes the switch I/O signal and basically amplifies it using a relay.
I have a new switch to go in mine this summer and will report the results. Had to wait a month for MSM to get it in from Japan, so they may be hard to get a hold of. If you look at the switch/sensor function section of your commander you should be able to see which fan setting the AC stays on with. I would use that speed until you do the new switch or relay mod to avoid wearing the compressor clutch.
It makes sense from an electrical standpoint that the lower speed switch contacts would hold out longer. The higher fan speeds have less resistance in the circuit, so the switch contacts see more current.
I have a new switch to go in mine this summer and will report the results. Had to wait a month for MSM to get it in from Japan, so they may be hard to get a hold of. If you look at the switch/sensor function section of your commander you should be able to see which fan setting the AC stays on with. I would use that speed until you do the new switch or relay mod to avoid wearing the compressor clutch.
It makes sense from an electrical standpoint that the lower speed switch contacts would hold out longer. The higher fan speeds have less resistance in the circuit, so the switch contacts see more current.
Last edited by alexdimen; Jul 3, 2019 at 09:25 AM.
Thread Starter
Full Member
Joined: Oct 2018
Posts: 63
Likes: 2
From: Arlington, tx
The root cause is probably bad contacts on the fan speed switch. The PFC is more sensitive to the poor connection than the stock ECU for some reason. The relay mod is a work around. From what I can tell that mod takes the switch I/O signal and basically amplifies it using a relay.
I have a new switch to go in mine this summer and will report the results. Had to wait a month for MSM to get it in from Japan, so they may be hard to get a hold of. If you look at the switch/sensor function section of your commander you should be able to see which fan setting the AC stays on with. I would use that speed until you do the new switch or relay mod to avoid wearing the compressor clutch.
It makes sense from an electrical standpoint that the lower speed switch contacts would hold out longer. The higher fan speeds have less resistance in the circuit, so the switch contacts see more current.
I have a new switch to go in mine this summer and will report the results. Had to wait a month for MSM to get it in from Japan, so they may be hard to get a hold of. If you look at the switch/sensor function section of your commander you should be able to see which fan setting the AC stays on with. I would use that speed until you do the new switch or relay mod to avoid wearing the compressor clutch.
It makes sense from an electrical standpoint that the lower speed switch contacts would hold out longer. The higher fan speeds have less resistance in the circuit, so the switch contacts see more current.
Thank for replying!
By the way what is that MSM you’re referring to?
If I’m understanding this correctly, the compressor clutch is powered by a 12v? For me I’m guessing there is an issue with the Power FC where the signal isn’t always there/working correctly/weak signal.
So the “replay mods” is just a replay that take the original compressor clutch signal (instead using it for the clutch, it use for opening/closing the relay, which should require less amp to open/close)
This relay supply a direct voltage to the ac compressor!?
Thank you
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