Taurus Car Club of America : Ford Taurus Forum banner
1 - 10 of 10 Posts

·
Registered
Joined
·
147 Posts
Discussion Starter · #1 ·
OK, here is the back ground. My AC does not work well unless I am driving down the interstate at speed. In stop and go traffic, it barely keeps up.

I pulled the car in the garage to check the pressures and I noticed the pressures would climb really high (300 psi on high side) and then they would start to lower. This was while I had the pressure switch shorted to keep the compressor running.

I noticed the cooling fans were not running all the time. When the high side pressure got to about 300, the fans (both) would kick on and then the high side (and low side) pressures would drop RAPIDLY. At the same time, the air out of the AC Vents would start to lower.

Then when the pressure (high side) dropped to about 220, the cooling fans would turn off. At that point, both the high and low side pressures would start to rise and so would the temp out of the AC vents.

I was able to get some diagrams for the electrical side of the fans, relays, etc... and I finally got the time to start poking around.

It turns out, the fans never turn on in slow speed. I am assuming that they should turn on in slow speed when I turn on the AC. Something is triggering the high speed fans to eventually turn on. I am assuming the ECM is seeing some engine temperature and turning them on (un-related to AC system).

I have verified the high speed relay and fan operation by jumpering across the two terminals for the high speed fan. When I do that, both fans turn on.

When I do the same thing for the slow speed relay, nothing happens. That struck me as odd, since there are TWO fans. Could BOTH be broken.

By the way, there is separate high and low speed windings on the fans.

I also did a continuity check on the wire from the relay down to the plug that goes into the fan and verified the wire is good for both fans.

The only thing I can think that would cause this is for BOTH fans to have an open in the slow speed windings. The fans use the same ground for both the high and slow speed windings.

That is where I would like a sanity/reality check from you guys. Is there something else I could be missing here?

I guess one slow speed fan failed at some point (and I did not notice) then the 2nd one failed recently and that is when I noticed the AC not working as well.

Thanks for any pointers.

Ken
 

·
Premium Member
Joined
·
14,126 Posts
I think the AC only uses the high speed fans. There is a dropping resistor in the passenger side fender well under the liner. This is what reduces the voltage for the low speed.
 

·
Registered
Joined
·
147 Posts
Discussion Starter · #4 ·
That's a different schematic from what I have in my car. I have 3 wires that go to each fan. One from the low speed relay, one from the high speed relay and the 3rd is the ground.

I think the difference in fan speed for my setup is just a different set of windings in the fan motor.

I hope to get one of the fans pulled out tonight so I can see if there is anything else to it.

I picked up a replacement fan today from Advanced auto.

I will check into the status of the control signals to the relays and see when there is a "turn on" signal for each relay compared to what the AC setting is.
 

·
Registered
Joined
·
147 Posts
Discussion Starter · #6 ·
yes it does appear there are two windings for the '99.
Yep, that's the diagram I have been using and it seems to match what I have under the hood.

My house is on the market and we have a showing tomorrow, so I haven't had the chance to get back under the hood. :angry: Looks like another week of sweating to and from work.
 

·
Registered
Joined
·
147 Posts
Discussion Starter · #7 ·
Problem Solved

OK, I am posting an update so anyone else that has similar problems can possibly benefit from my experience.

I tried to purchase both fans locally. It seemed the part stores only carried the Drivers side fan for some reason (Dorman part # 620-106). The passenger side part number is 620-105.

So, I figured having one side working in slow was better than neither side working, so I set out to just replace the driver's side fan.

I was hoping that the fans would be symmetrical somehow, but the fan shroud is shaped in a way that the two will not swap.

I had to remove the relay box that is above the driver's side fan. I also took off the wire that connects to that box coming from the alternator, so I could swing that box out of the way to get more clearance. There is only a single 8mm bolt holding the fan in place. The bottom fits into a could slots. The button release for the wiring harness is somewhat hard to get to. Definitely have the engine cooled off or wear gloves and work quickly.

I checked continuity on the slow side winding for the driver's side fan, and it was indeed an open.

I put the replacement fan back in and plugged in the harness. I then jumpered across the load side where the slow speed relay goes. I was hoping the new fan turned on, verifying that I actually fixed PART of the problem. To my surprise, BOTH fans turned on.

I am guessing the wiring diagram that I had gotten is not correct for how the two fans are wired. I am guessing the way it gets slow speed is by putting the two fans in SERIES, so each fan effectively has 1/2 the normal voltage. I am also guessing there must be a problem with the driver's side failing and not the passenger one. That must be why all the local part stores carried the driver side fan but the passenger side one was "special order".

Going to the question about whether the AC causes the fans to turn on in SLOW or FAST... I just verified that both fans turn on in SLOW speed when you turn on the AC. Then, at some point the computer sees the engine temp getting too high and turns on the fans in fast (that's all that happened before for me).

I verified the slow speed fan operation with AC by checking them with the AC both on and off, and then when the AC was on (fans running) I pulled the slow speed relay and they went off (verifying it was slow speed and not fast speed).

Sure glad to have this resolved. I have been dealing with less than optimal AC in my car for over a year. I kept thinking it was a leak (charge always seemed OK) or something more terminal like the compressor going bad.

Oh, the fan was about $60 from Amazon.com, or $129 at the local stores (Pepboys, Autozone, Advanced Auto).
 

·
Premium Member
Joined
·
14,126 Posts
If the fans are wired in series then there should be continuity between two of the three wires. One would be ground to ground and the other would be the low speed.

You can easily just replace the motors and not worry about which shroud you have. There is only a large thin quick nut that holds the blade on. Then the motor comes out. Same motor fits both sides.
 

·
Registered
Joined
·
147 Posts
Discussion Starter · #9 ·
The replacement motors cost the same as the whole assembly, and they had different part numbers for the passenger and driver side fans.

I never did a continuity check between the two fans connected. I had the driver side fan on on the garage floor, check across the two pins and it was an open (about 3 ohms for high speed connection). So, I know that fan was definitely bad.

It just really shocked me (pleasantly) that the fan I did not replace started working once the other one was replaced.
 

·
Premium Member
Joined
·
14,126 Posts
I was thinking of used motors. I meant check the contiunity of the harness.
 
1 - 10 of 10 Posts
Top