1999 2000 Windstar A/C not kicking radiator cooling fans on

[LTDzak]

1999 Windstar, 160 K miles on body and AC, 40 K on transplanted 03 engine.

Went to charge up the air conditioner the other morning and realized that the cooling fan was not coming on. The static pressure was pretty low, 60 psi or so before opening it to the R134a can. Disconnected everything and went for a ride to fully warm the engine/trans. Idled it in the driveway waiting for the fans to come on (no AC) and they didn't - key here is I only waited 4 or 5 minutes.

I got a new low speed fan relay from Ford. While putting it in I pulled the drivers headlight and looked at the dropping resistor, it looked ok (you have to look in the turn signal hole it is a white elongated U shape). I did not pull the fender liner to put a DVOM on it but it seems functional as you'll see.

With the new low speed relay and engine cold I started it up and went to max AC. No fans came on. I had seen a thread or two mentioning the high pressure side AC switch and how it had different failure modes. I decided to disconnect the high pressure switch. and viola the fans came on as soon as I put the AC on - first on low for about 30 seconds and then on full high. Having found the culprit (or so I thought) I reconnect it. Now with the engine running and AC off the fans run continuously on high. Great, easy fix just replace the high pressure refrigerant switch, right?

$109 later (whether you go to NAPA, or dealer -20, cheaper on evilbay) I had a new switch and a new O ring. This is the 6F9Z-19D594-AA switch that superseded the original F6CZ-19D594-CB part, at least according to fordpartsgiant.com and an interchange on one of the rockauto options (also appeared to cross on NAPA's online system). Oddly looking it up at the dealership for a 1999 Windstar did not show it cross over but am seeing more of this on older models - they just don't bother updating the computer system for older Fords - way to encourage customer loyalty Ford..

Put the new switch and O ring in and started it up - no cooling fans with the AC on. Went for a 5 mile ride to warm the engine up. Let it idle in the driveway for almost 10 minutes and finally the low speed fan kicked on for a short while.

Thinking about it, perhaps the high pressure switch kills the fans during AC if it doesn't see enough pressure. Put half a can in it, then disconnected the high switch to get the fan to run on high and added a second full can. It is still short on freon but high side is up over 100 and not short cycling too crazily. Reconnected the high switch and still no fan operation at all with max AC and the button lit.

Am trying to find my code reader to see if there is some code that needs clearing (no check engine light). Hopefully it’s not the PCM because those are around 200. Any ideas on what else to check here? Absent any will try to fully charge the AC via the disconnect trick.

Sorry for the novel, did not want to leave out any pertinent detail. Here are some related threads with some great posts by 12ounce and others on similar situations:

http://www.automotiveforums.com/t932...always_on.html

http://www.automotiveforums.com/vbul...=732240&page=2

[LTDzak]

One other item to mention,recently had the interior bezel etc. off to replace the blend door actuator

On edit, checked for diagnostic trouble codes (DTC) with the reader, key on engine off, nothing stored.

[scubacat]

A/C systems show weird symptoms when not charged to spec. I'd definitely charge it to the correct level before worrying about any of the symptoms. The switch you're talking about is called a "pressure transducer". If the system is at a lower charge, it may not have enough pressure to trigger it and cut on the fan. Obviously I'm no expert and that's just a theory, but regardless, I wouldn't worry about anything at all without first establishing a proper freon charge.

[scubacat]

FYI, the switch is about $60 on rockauto. (There is a $24 option, but somehow I don't trust that one. It's probably fine though.) They call it a "Refrigerant Pressure Switch".

[LTDzak]

Yes, the issue was the AC pressure being too low. I disconnected the pressure switch (which ran the fans on high), got the system fully charged and then reconnected it - works properly now although only low fan comes on after engaging the AC.

The rockauto switch for 60 is ideal if you have time to wait for shipping, I didn't, all the local stores wanted 110-120.