Laminar

I'm working through the wiring diagrams now to make sure I have my ducks in a row. From the PCM I see:

- 1AN - R/L - 0-5V ECT temperature feed from PCM to the A/C amplifier (ECT (A/C unit))
- 1I - G/B - ground switch output to activate A/C relay to engage A/C clutch (A/C relay)
- 1AU - LG/R - ground switch input A/C request from A/C amplifier through NC refrigerant pressure switch contact (closed between 30-341psi) (AC Control)
- 1J - R/B - ground switch input through NO refrigerant pressure switch contact (closed above 232psi, open below 161psi) (AC Load)

The relay control and A/C request are clear, but I have questions on the other two.

How does the A/C amplifier take ECT into account? I can see it preventing the compressor from running based on ambient air temps, but why would it care about coolant temps?

I'm assuming the PCM uses the 1J terminal to monitor pressure and cycle the compressor off when high side pressure gets over 232psi and back on once it falls under 161psi.

Am I missing anything here?

SparklingFresca

I believe the compressor runs whenever the defroster runs or the floor/defroster combo runs but the indicator light is not on. This would likely be some side loop logic to not cool down the cabin in this mode, but to remove moisture from the defrost cycle. I am not sure of the parameters or logic beyond this point, but I am pretty sure all cars act this way.

Laminar

That makes sense - I'm just wondering if I'm missing out on anything if the A/C amplifier doesn't have an ECT signal. I'm browsing the factory manual and nothing is sticking out at me.

Stubbs

iTrader: (1)

It depends on which AC system you have.
For the Full Auto AC system(found on the higher spec)
Take a look at the 2009 Service Highlights https://foxed.ca/rx7manual/manuals/M...ght%202009.pdf HVAC info starts on Pg. 176. It walks through the control schemes and components starting on Pg. 184.
The short answer is the AC Amp uses the ECT to vary the position the blend door to match the requested temperature in full auto mode. It has to know what the coolant temp passing through the heater core is in order to supply the correct amount of heated air to blend with the cold air coming from the evaporator to output the requested cabin air temp. It also will delay the blower fan when the coolant temp is below a certain value to avoid blasting cold air on startup on a cold day.

For the Manual AC System(found in base models)
I suspect it's similar to the S1, but with a bit more control. I haven't found the exact purpose for the ECT in this system. In my swap I do not have an ECT signal going to the AC Amp and it operates normally.
It may be used to fine tune the blend door actuation based on coolant temp and the position of the temperature switch.
Another potential would be for emissions. A cold engine has slightly higher emissions, limiting how much the blend door opens when the engine is cold reduces the heat pulled by the heater core and the engine comes to operating temp slightly faster.
It might also be used for a last ditch engine protection mode. If the coolant temp rises above a certain value it may shut off the AC compressor and open the heater blend door to try to dump engine heat through the heater core.
I haven't found any documentation confirming any of this though.

Laminar

Ahhh! That's connecting some dots now. I was so fixated on A/C I forgot that the amplifier controls heat as well.

I have the manual A/C setup but I've considered converting to auto. I know the blower in my truck stays low until the ECT reads around 140 and then it will ramp up the blower speed. Thank you!

Laminar

Thinking about this some more, the A/C amp interprets a lower ECT signal voltage as a higher coolant temperature. If I tied that value to ground, it would see 0V and assume max coolant temperature. Assuming there's not some kind of smarts looking for an illegal value that would throw a fault, the only downside is that I might get incorrect blower speeds or blend door positions during engine warmup. Normal running behavior should be unaffected.

Stubbs

iTrader: (1)

Do you have the Full Auto AC system or Manual?
I don't think grounding the ECT pin is necessary and it's rarely a good idea to short pins to ground.
On a Full Auto AC Amp it will react the same whether the pin is shorted to grounded or disconnected.
Look on Pg. 180(07-02-3) of the PDF I linked previously. The AC Amp sets failsafe values if it detects a value out of range. If it detects an ECT value that indicates an open(pin disconnected) or short(pin grounded) then the AC Amp uses a default value of 176ºF.

It's unclear what the Manual AC Amp does in this situation, but it probably has the same failsafe operation.

Laminar

My car came with manual but I have everything to convert it to Auto. I just have to decide how much I want to hurt myself.