I know . . . I know . . . this has been posted and reposted and then reprimanded for being solved, but I can't figure out my problem.

My 1990 honda accord EX (2 door manual transmission) has been giving me head and back aches. The reason for the issue, the coolant fans just don't engage when they should.

I've been troubleshooting this ALL weekend and made almost no headway. I'll try to post in order of things I've done:

1. Jumper for the connector on the cooling fan switch in T-stat housing (green connector with white/green and black wires running to it. This initially worked to engage the fans. GREAT! I don't have a fan motor problem. . . I figured.
2. Heat up car to normal operating temperature (used IR thermometer on the t-stat to gauge coolant temperature.) Fans never engaged.
3. Found the shop manual and followed the troubleshooting steps: (see pages from accord 1990 - 1993)


4. This led me to believe I needed a new relay. I tried switching the power window relay with the cooling fan relay, but it didn't do any good. I could still roll down windows and still got no fans engaging. You can see my path in red. I also considered pursuing the next section, but I don't know what 2 pin diode 15-50 is talking about half way down, and I couldn't determine whether my car is KY or KQ (what do these even mean?) and struggled to find any sign of the cooling fan timer. I've looked under the dash, but it's REALLY cramped down there. Unless the cooling fan timer is up behind the cruise control box under the driver side dash. But the picture I have doesn't match my expected colors of wires and such given the manual. I took the picture below. The red square is the cruise control box, and the red circle is what I'm thinking might be the cooling fan timer? I'm still not sure if my car has one of those, since the steps above suggest that only Kq and KY should troubleshoot it.


5. Run a ground from valve cover to the engine bay (I noticed it was missing and thought maybe it would help. . .plus some forum suggested grounding as a potential issue.)
6. I decided to revisit the green connector with a jumper and this time the fans wouldn't engage! What?!
7. Jumper on the cooling fan relay again terminals 2 and 4, again the fans worked.
8. Decided to test the green relay connector on the T-stat fan switch. Determined that one terminal on the connector had a little over 12 volts and the other appeared to have continuity with only a little resistance to the nearby ground.
9. Checked continuity of the fan switch once the T-stat external temperature was 180+ and there was no continuity. This makes me think maybe the t-stat or the fan switch needs to be done, but I'm concerned since jumpering the green connector no longer kicks the fans on! So even if I DID have continuity on the fan switch, the fan still wouldn't run.
10. My AC doesn't work, no freon in the system since there's a massive leak. But I DID do the test with the AC button on and then used a jumper on the AC pressure switch and got positive results! Meaning that I could make the car turn on the fans by convincing it that the freon was appropriately filled and that the fans needed to kick on. Again, evidence that the fans are in good shape.

11. So I stood around trying several different things and testing the T-stat temp, trying to jumper the green cable after making adjustments in the wiring harness, or at different temperatures, then suddenly, the fans kicked on. Probably only for 10~15 seconds, (both fans) and then they stopped! What on earth? So I kept watching while talking to my neighbor and the next time the fans kicked on, I unplugged the green connector on the t-stat fan switch and the fans kept going! Only for the 10~15 seconds again. The next time it kicked on, I disconnected the AC pressure switch (thinking maybe the car was tricking itself into turning on for AC purposes, same result, the fans kept blowing for around the same time. Lastly, the next time it kicked on, I pulled the cooling fan relay out. That shut the fans off in a hurry. But when I plugged the relay back in, they continued to run for around 10~15 seconds.


Note: I think the coolant temperature sending unit is bad since my temp guage lies flat most of the time. I can get it to move up to the right temp by pounding lightly (sometimes not so lightly) on the dash above the gauge. When the gauge is working, the sending unit has appropriate continuity, when the guage is flat, the continuity is out of whack.

I cannot figure out what's turning on my fans and why they won't turn on when they should for normal operating temperature/ when I jump the wires in the green connector and make it THINK that it's at temperature.

This car has 312k miles on it. So I know that ANYTHING could be broken. I also don't know whether some of these things could be contributing to the problems I mentioned. I'm ordering the sending unit from Rock Auto right away, and I think I'll pull and test the t-stat in the next couple days.

Any ideas are welcome, and if my logic is flawed, please let me know. I'm certainly amateur at this, though I try to be thorough.

Thanks in advance!

 

If you can jumper the fan switch at the thermostat assembly in the back of the engine and the fans work, but they don't work normally then only two things are happening, either the fan switch is bad or the connectors therein are bad, or there is an air pocket at the thermostat housing that needs to be relieved by cracking open the bleeder bolt for a few seconds to relieve all the air.

 

Thanks for the reply. Initially I COULD jumper the connector for the fan switch and the fans would run, but now when I jumper that connector, nothing happens.I'm going to try to bleed the system a bit more, I did a half job of bleeding it at one point, but I only bled it at idle and even then not very much.

I guess what baffles me is that the connector at the fan switch DID work, and now doesn't, and the jumper at the relay still does. Then further, I can't figure out why the fans are turning on briefly when the t-stat is ~210.

 

Well, I have to eat crow.

I think I was jumping the wrong switch! The water return from the engine going into the top of the radiator has a switch on it, and I thought that was the t-stat housing. Stupid. I now realize that switch A comes from the lower radiator hose and the t-stat is back by the bleeding nipple. I bled the system thoroughly, but didn't seem to get much air coming out. I also jumped the connector on that sensor and found that the fans kicked on with no problem! I'm now fairly certain it's just that fan switch that needs to be replaced. I'm guessing that the water return switch (switch B) was initiating the fans for the random 15 seconds or so.

I'll update once I get the new part in.

 

Well, I replaced the cooling fan switch tonight. I decided out of curiosity to test the old one with the boiling water method. I found that the part I pulled off seems to be working right. (Once the water gets to ~200 degrees F, the switch appears to register continuity.

Could it be that during the cold Utah winter, my car just doesn't need to kick on the fans almost ever? I feel really stupid if I just spent all weekend troubleshooting something that wasn't really an issue, but that's what I think happened.