davesan1

iTrader: (4)

I've read the many posts on how the fans operate. on my '93 RX, my fans never appear to run at low speed. The first time they switch on is round about 108 degrees C, which I believe is when the Thermoswitch operates, (relay 3). They come on then at fairly high speed - I assume it is at least medium speed, as it should be. However, according to the service manual, they should come on at low speed at around 105 degrees C via the Thermosensor and the ECU route, (relays 2 & 4). I guess one possible culprit is the Thermosensor itself not starting to operate at a low enough temperature, but then I would expect other engine-related symptoms due to the other ECU uses of the Thermosensor input. Alternatively there could be a connector or loose wire issue. I do not suspect the fans themselves because it is unlikely that both fans would fail the same way on the low speed winding, (inputs B and C). The relays seem OK, (they all close correctly and make a short circuit through the contacts).

So that's where I am, and I'm about to dig into it deeper. However, before I start, advice from anyone who has had the same problem would be most appreciated, especially if there is some sort of common failure mode, connector often coming loose, etc, etc.

By the way, I am aware of the of the "C-version" THERMOSWITCH swap out fix. I have the part and will shortly install it. As I see it, by and large this conceptually should "override" the ECU-driven low speed mode by activating medium speed at less than 100 dgrees C. However, according to the service manual, the medium speed operation mode caused by the Thermoswitch also requires that relays 2 and 4 be operating via the Thermosensor/ECU route, i.e. as for the low speed mode. Thus if my low speed mode is not operating, the medium speed mode will not operate either, (see F-144, operation table)! Got to admit I'm a bit confused here. It seems that the Thermoswitch is intended to provide the final "ultimate safety" mode in case of potential overheating, and should therefore ideally not rely on other failure-possible areas to operate, (ECU output, etc).

Note that I see the use of the term "Engine Coolant Temperature Switch" in the F section of the manual, (F-144). I assume that this is the same as the Thermoswitch. To make sure that my overall understanding is correct, would somebody also please confirm the following is true:

There are 3 water temperature sensors:
1) Thermoswitch-This is an ON/OFF switch going ON at 108 degrees C and over, (approx 98 degrees on the C version). It is used to activate the fans to medium speed.
2) Thermosensor. This has an "analog" type operation, having varying resistance as the temperature changes. It is used by the ECU for engine control functions and also to switch on the low speed fan mode at 105 degrees.
3) Another sensor, (on the main body of the engine). Analog sensor, as above. Used to operate the stock temperature gauge

Thanks for your help

Dave

davesan1

iTrader: (4)

Bump! Calling all fan experts - I know you;re out there!

Thanks

KevinK2

"according to the service manual, the medium speed operation mode caused by the Thermoswitch also requires that relays 2 and 4 be operating via the Thermosensor/ECU route, i.e. as for the low speed mode. Thus if my low speed mode is not operating, the medium speed mode will not operate either, (see F-144,..."

This "conditional" med speed logic, per the circuit diagram, is true on some models, but most FD's will give you a lower med speed fan by slapping in the FC switch. (this may be due to the harness change and new fan controler added as a faactory TSB). A lot easier than probing the the relay cluster to see what's going on. The simple test is to ground the thermoswitch wire with engine cold, ign-on. If fans come on, no "low speed conditional" clause)

(I always wondered how the ecu could kick in a fan exactly 3 deg sooner than the switch, given the resistance vs temperature tolerances listed in the manual)

adam c

iTrader: (2)

You may want to check your fan relays to make sure they are all plugged in properly. Sometimes the plugs get old, and they come apart. The relays are located near the top of the passenger side front strut tower.

Kento

As has been noted by others, you have a fan relay problem. Unfortunately due to their location (on top of the passenger fender well), it's very easy for problems to occur with wiring, contamination, heat degradation, etc. Also, as DaveW stated, the reason that your medium fan speed operation still works is most likely due to the factory TSB update fan controller unit and wiring harness.

While installing an FC thermoswitch will give you earlier medium fan speed, I'd still diagnose the problems with your fan relays. That way, you'll still get low fan speed at an early stage to perhaps ward off the need for medium speed.

davesan1

iTrader: (4)

Thanks for your help everyone.

I checked all the relays again and, indeed, one was loose, (not latched into its socket). Not sure whether this is the cause or not. Will check it out today. BTW, anyone know which position each of the relays 1 , 2, 3, 4 is in, (position in the group of 4, so I can tell what the suspect loose relay was/is supposed to do)? Could not see this in the manual.

KevinK2 - Ref the grounding of the thermoswitch wire, where is the best place to get to it? I can't even see the thermoswitch in situ, it's well down behind pipes, etc. Does it go elsewhere where it is easily accessible so I can short it to ground?

I assume the factory TSB has been done, although I've never heard the fans run after ignition off. Should the TSB # be on the door? All I can see is Campaign # SSP39. (could be 55P39)." My list says campaign # 60504 for the fan fix. Any other easy way to
tell if the fan fix has been done?

Thanks again

Dave

KevinK2

from FAQ section -->Fans

http://www.scuderiaciriani.com/rx7/fan_mod.html

the test wire by the fan module (see link) is easily acessed, and will ground the 226F thermoswitch.

check "voodoo" link in faq too for relay orientation.

Kento

I wouldn't take that as gospel, however, as it's very easy for some mechanic who previously worked on that area to replace them in different order. I discovered mine were switched around on the bracket (previous owner).