Power FC and AC
 

I have a 1993 Touring Model and RP in Dallas just installed a new engine in it. With it, I had them put in a Power FC, and everything seemed to be fine when I drove it home, except for the Air Conditioning. The Power FC has the new software, version 5.0. I was told there wasn't an AC problem with this version, but I guess that's wrong. The thermostat behind the glove compartment has been bypassed, and so has the thermostat on the coolant line coming off of the condenser. The only thermostat that hasn't been bypassed is the one that is actually in the compressor. I have bypassed the power FC controlles for the compressor, and acutally got the compressor to run, but then it doesn't idle well, or at all, and the AC is intermittent. It surges between 300 and 1100 rpm at idle, and the AC will work fine for one minute, then blow hot/humid air for about a minute, then back to cool air.. etc.. It wouldn't do anything at all before bypassing the two thermostats though. After bypassing the thermostat, I decided to try to get the power fc to controll the AC again as that would fix the idle by adding in the AC idleing mode availabe with the power FC. Even after bypassing the two thermostats, the compressor will not start while the power FC is hooked up at all. This is getting extremely frustrating, as it is just about the last of my problems with the car. Any ideas would be very helpfull.

-Quinn Carman
1993 Mazda RX7-Touring
Mazdaspeed Short Shift Kit
Blitz Front Mount Intercooler
Toyo Radiator
Apexi Power FC with Commander
Greddy power extreme exhaust
Bonez downpipe and midpipe
Milled out wastegates
RE Amemaya Intake

Ah the lovely AC problem on the PowerFC. Well if bypassing the PowerFC does not work, then you have to be sure you have the correct amount of R134 or R12 in your system otherwise the pressure switch will cut off the AC. The next problem is when an AC system that works 100% correct is getting the the engine to up its power under the heavier AC load. The current fix being looked into by Chuck W. is a modification to the electrical load box to boost the idle rpm when the AC is kicked on. There is no means to do this when you bypass the PowerFC so something must be added to do this function.

There is only one thermo switch for the AC and that is the one behind the glove box. It's main
function is to prevent freezing in the evaporator
coil. The switch up near the dryer is for low or high pressure. This is to protect the compressor
from high pressure or loss of freon.

If you have bypassed your PFC as described in my previously posted AC bypass fix, and your AC is still erradict than you have REAL AC problems not PFC problems.

I set my idles as: A-E 850, E/L 850, and A/C 950.
Then I fine tune the idle with the air adjusting/bleed screw to cause the idle to be on the edge of the limits the PFC can handle. This causes the revs to drop very slowly when letting off the throttle. Like from about 1100 down to 850 without any load such as light or AC.
With load it drops normally to about 850.

This adjustment is not something I can really explain in words. It takes "BEING ONE" with and
"UNDERSTANDING" you particlar car. It is a ZEN
thing!

Got it!
 

Found the problem! The "experts" at the AC place had put 2 psi too much, and causing the condenser to switch off. Talk about finicky! Oh well, it works great now. And I figured out how to get the Power FC bypassed while keeping the third AC idle function. Just take the violet wire and crimp it to the other two wires that you have crimped together for the bypass. It will allow the Power FC to sense the AC is on, but still allows the bypass to function as it should. My car is now working great.. now onto the alignment issues.. :) Thank you guys for all your help!
-Quinn Carman

Hmmmm
 

It was working great.. AC runs for a while, then starts blowing humid air. I think the compressor is cycling off. It then blows coolish air, but it's quite humid. You can actually see it coming out of the central air vents. I wonder if I need a new drier, it is kinda old. This is getting very annoying. Oh well, thanks in advance for any advice you guys might have!
-Quinn

Mine did something similar when I first started using the AC this summer. Then it went away after my low freon was filler. From my testing results, I think my thermo switch in the evaporator coil was sticking open after it got cold. Maybe it got too cold and took too long to warm back up so the circulating air got humid from the ice. Low freon can cause this problem.

Since you had too much freon, then had it reduced; maybe your switch is going bad. It takes too long to shut the AC off which causes freezing. The air citculates around this ice melting it and absorbing moisture.

Just a wild speculation.

Power FC glitch with AC
 

I'm confused, and don't want A/C problems when my Power FC goes in.

I'm having a ported built, with a few bolt-ons added. Everyone has told me that the Power FC is the best choice for ported motors, uncorked exhaust, and upgraded intake and ICs.

Now I'm reading about this A/C glitch with the Power FC.

Is this something that can fixed by the person installing my Power FC?

I haven't a clue with regard to red, blue, violet wiring. You guys sound like the bomb squad doing a defuse job :)

FWIW, I'm hoping to purchase the Power FC from Jason of the Rx7Store.Net

I have a 94 PEG with the A/C recall (little black box near the ECU). I've never had a problem with the PowerFC and A/C.

Just thought I'd share that it doesn't affect all cars.

-Scott

OH good. I feel better now :) Yes that thermostat switch went out on my A/C two summers ago.

I just unplugged my ECU and plugged in the Power FC, no snipping any wires, etc, etc. Everything works fine, A/C included..

Which version of the Power FC did you get?

I just removed my AC condensor and all plumbing associated with it but it left in all the wiring and everything for the AC, am I going to run into any problems not having those sensors plugged in or would that only happen if I were to try and put the AC on?
short:will my car run fine without any PFC/sensor/wires manipulation with the above stated?

probably a dumb one but...
Paranoia...

My a/c seems to only work when on fan setting 1, settings 2,3,4 do not work at all-as per checking the switch on/off thingy while monitoring with the power fc- it is the newest version

Does anybody have any ideas- everything worked fine exactly, before isntalling the pfc, but could this be related to the thermo switch in/behind the glovebox?

Mmmmm... Hopefully the latest? I remember seein a 5.0 or 5.08 whenever I turn it on.. Can check @ lunchtime when I go out to my car.

R1 and PowerFCs are the well known problem. I found there is too much voltage drop in the wires and if I run a new wire from the thermoswitch directly to the computer the problem is still not bad. The main problem is that the stock ECU will trigger at 3V and below. When the AC is off the voltage is around 12V and with it on fan1 about 1.4V, fan2 1.8V, fan3 2.4V, and fan4 2.1V which explains why fan3 almost never works, fan1 is ok, fan2 & fan4 are so-so. The voltage needed to trip the Apex is right around 2V instead of 3V. I've been meaning to make a circuit to convert, but seeing how it is winter time I haven't seen the need.

Mine's 5.08.

i have a 93 touring and i just intsalled the PFC my a/c worked fine before this but now it only works on setting 1. 2,3,4 do not work at all they blow humid air just like "race 1" said is there a fix for this?
Note: I NEED a/c i live in Miami

My new engine to ECU wiring harness solved my PFC A/C problem. So I removed my bypass.

Attached is my bypass.

Chuck: Well if this is the case, then the only thing I can add is that the ECU isn't being grounded well enough through the harness. The grounds that are affected via the ECU to engine harness are pins 4A, 4B, & 4C which are two wires ... B & B/W. I'm going to go T-tap them and run them to chasis ground and see if that helps.

So do you think the car is running better with a new harness?

When Mazda did the cooling system recall and installed the black fan mod box, they also installed a jumper cable between the ECU, engine and chassis harness.

The new harness does not use this jumper, as it is directly wired to the black box. All along we knew the PFC had a grounding problem, this partially fixes it as A/C fan speed 3 will still mess up once and a while.

The new harness was installed because the old one had too many broken connectors , and wire corroding
even where it was covered.

This way I know for sure all sensors, etc., have good connections.

I thought you replaced that harness like 3 years ago?