mecman

iTrader: (11)

Hi guys,

I need your expertise. My A/C last year stopped working on fan speed 4 but worked on 1-3. This year only 1-2 work. When I move the fan speed up to 3 or 4 the compressor kicks off. I replaced the A/C relay but that did not change anything. The FSM schematic shows a resistor bridge for the fan speeds. Anyone know where that resistor bridge is? Or have any ideas on what might be going on? It works perfectly on fan speeds 1-2 under any driving conditions.

Dale Clark I need your expertise!

HalfSpec

iTrader: (14)

The blower resistor array is at the bottom of the blower motor. It's actually where the 6 pin connector plugs into the blower. The resistor array screws into the bottom of the blower with 2 screws. Since you're referencing the FSM, I'll give you a tip that'll serve you in the future. When you look at the resistor array on page Z-68 on the FSM you'll see that the it's connector name is G-07. To locate G-07 simply turn to the next page and look to the bottom right of the page for G-07

You're problem is an interesting one. The AC signal makes its way though the AC switch and resistor array through the L/Y wire that attaches to the position 1 wire between the switch and the resistor array. To activate the AC system and the compressor that wire has to see ground. The only way positions 3 and 4 wouldn't have a path to ground is if the center resistor were blown... but if it were blown, the blower wouldn't work in positions 1 and 2.

If you're curious exactly how the AC switch signal works through the resistor array take a look at the electrical section here (scroll down):
http://www.norotors.com/index.php?topic=12654.0

1/2 of it is related to LSX swaps, but the other half is a circuit analysis of how the stock AC signal works.

Lane

IRPerformance

iTrader: (41)

That's usually an issue with the pfc not seeing the ground from the climate control panel.

https://www.rx7club.com/power-fc-for...-c-fix-435420/

I use the relay method.

mecman

iTrader: (11)

Thanks HalfSpec! I will look into how to replace that. I appreciate your help.

IRPerformance, thanks for your suggestion too but i have had a PFC for few years and it was only this summer that I had this problem so I cannot understand why my PFC would have a problem with seeing the ground now? Others have mentioned this to me too but I figured since it never had a problem before why would it now?

Mazderati

iTrader: (3)

^ Apparently the problem shows up when the contact points for the fan speed dial become dirty. Which can occur over time. Or something like that.

HalfSpec

iTrader: (14)

Actually, if you have a PFC, I'd take IRPerformance's advice over mine. His suggestion makes sense and is a solid path forward.

The reason it makes sense is that it provides a better signal for the PFC. Like Mazderati alluded to, the stock wiring, switching, and resistor packs are all sources for contact problems. The resistor pack and the switch are especially good culprits. The AC signal requires that both the switch and the resistor pack provide easy paths through, electrically, to work. Add 20 years of switching and 20 year of heat cycles on the resistor pack and you can develop some extra resistance that can affect the PFC or the stock ECU's function.
The PFC diode or relay fix just insures that the AC signal has an easy/efficient path to take.

Lane

bajaman

Still, it is worth checking out the resistors...the ones I've seen bad (on other cars, albeit) are OBVIOUSLY bad...easy to see. They'll have missing wire elements or fused solid elements, etc.

DaleClark

iTrader: (55)

FYI, the fan resistor pack is ONLY for the AC fan blowing air in your face. With that pack bad or messed up, speeds 1-3 result in NO air coming out of the vents, but speed 4 is fine. It has nothing to do with the AC compressor engaging or not.

Your problem sounds like the classic PFC AC issue.

Dale

HalfSpec

iTrader: (14)

I'm sorry but that's incorrect.

While it's true that the blower fan does use the resistor pack to drop its voltage on speeds 1-3, the resistor pack also facilitates a ground route for the AC switch. Why go through the trouble of routing a ground through a resistive element? Well, it's a complicated way to make sure you can't activate your ac compressor or fan relay # 1 without the blower switch being in positions 1-4.

If you look on Z-68 of the FSM you'll see what I'm talking about.

Focus on the AC switch on the lower right. Notice that it's normally open. See the leg that exits out of 1G. That's the path to ground. How? You'll see it make its way to position 1 of the blower switch. When you switch the blower switch, this is how it gets ground.
Position #1 = Direct patch to ground through the switch
Position #2 = Path to ground through the diode then to through the switch
Position #3 = Path to ground through the diode then through the second resistor then through the switch
Position #4 - Path to ground through the diode then through the second and third resistors then through the switch

So that describes a path to ground for positions 1-4. That path to ground, grounds and activates fan relay #1 to get your fans going to cool your condenser when you activate your AC system but it also grounds ECU pin 1E which signals the ECU that AC is being requested which in turn activates the compressor relay via pin 1L.

Lane

PS
I'll also add that this isn't just theoretical circuit analysis. I build AC controller wiring kits for the LSX swap guys whose basis for working hinges on the facts above. It's also the basis for the PFC AC fix in the link IRPerformance posted.

IRPerformance

iTrader: (41)

Wiring in these cars is old. Sometimes they work. Sometimes they don't.