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Discussion Starter #1
Hi TCCA,

The A/C on my 1993 Taurus stopped working last week. Fyi - the A/C system was replaced last year (everything except the OEM evaporator and condenser coils).

Since the A/C had been working fine for me on a trip to the store, and suddenly did not work when I came back out of the store, I threw out the idea that the A/C system had lost it's charge in a matter of 5 minutes just sitting there.

I tired the usual troubleshooting technique of pulling the electrical connector off of the evaporator dryer, turning the engine ignition switch on, and the bridging the connector: The A/C clutch did not "click" on as it should have.

This breakdown reminded me of the time that the fuel pump in the trunk stopped working a couple years ago. That ended up being from a failed RCM (ie. Relay Control Module). So this time I made an educated guess that the RCM had failed again, but this time for the A/C clutch circuit that it services.

Last time I needed a new RCM, I bought one from AutoZone for ~$80US and it lasted only a day. I then got one form NAPA which only lasted a day. I had to bite the bullet and got one wholesale from Ford for $110US. That one has lasted about two years before it failed. This time I was lucky enough to find one on eBay, bid on it and got it for $30US delivered. I thought I was very lucky. I installed it this morning and the A/C clutch is instantly back on line.

I wanted to see what failed in old RCM, so I drilled out two rivets, and I could see that the smallest relay (ie. a little black cube) was burnt an bulging out on one side (see pics in the links below). Hence the A/C clutch problem. I was still able to read the manufacturer's name and part numbers on the relay. I Googled this:

omron "G8SN-UA-007116"

That returns two very informative how-to links:
http://www.feoa.net/modules.php?name=Forum...ic&p=401224
and
http://www.2carpros.com/forum/2-vt39929.ht...sc&start=10

The upshot is that you can fix the A/C relay problem for less that $5 at Radio Shack with P/N 275-005. I will be fixing the old RCM and keeping it in the trunk for a spare. Believe me, that failed fuel pump scenario is not fun.

I'm getting tired of replacing these so I've come up with an idea that I'm going to try this week. I'm betting that the main reason these RCMs fail is due to thermal breakdown of the relays. Look at it this way, these RCMs get so hot that Ford mounted them in the front of the car on top of the radiator to try to catch some wind. I have a 2" X 4 1/2" heatsink with a fan that was used for Pentium II computer CPUs. Thermal epoxy is expensive, so I ordered two 1" X 6" strips of thermal tape from eBay for $3US delivered. See the pic below for a mock-up of what this contraption is going to look like. I'm not sure how long that fan will last out in the elements (but they're pretty inexpensive). Also - I'm going to have to either leave off the plastic cover that covers the top of the radiator, or, cut a square hole in that cover for room for the heat sink to stick up out of.

Hope that helps someone. And as always, your comments or suggestions are welcome.

Regards,
Brcobrem
 

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Discussion Starter #3
QUOTE (Qwertz9586 @ Mar 12 2009, 04:49 PM) index.php?act=findpost&pid=707989
Interesting idea, but the hood might not close with that thing on the CCRM.[/b]
Hi Qwertz9586,

I still have that plastic shield that fits over the radiator/RCM removed. It's the big flat black piece that has all the belt routing and emissions diagrams on it. I'd like to have that back on there because it makes a nice place to place tools when working under the hood.

Yes, I agree, if it's going to hit the hood (when closed) I'll have to consider other options. I'm anticipating having to cut a 2" X 5" square hole in that plastic shield for the heat sink to stick up through. I'll make sure it's going to fit before cutting the plastic. I've already taken some photos of the existing diagrams to put a copy in the glove box.

Let you know how it goes. Waiting for "thermal tape" to arrive from eBay. That's how I'd going to mount the heatsink on top of the RCM (way cheaper that thermal epoxy).

Btw, below is a pic of the RCM opened and the new (blue) relay awaiting installation.

Later . . .
Brcobrem
 

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Discussion Starter #4
Hi TCCA,

I finished the rebuild of the RCM with a new A/C relay. I also attached the heat sink I mentioned previously.

I have a solder sucking solder gun (ie. it has a vacuum bulb that you squeeze to suck up liquid solder). Even with this very hot tool, it took some time to get the solder removed from the old relay pins enough to get it pulled off the board. You might want to have your local electronics person do this for you. It wouldn't take them more than 10-15 minutes if you had the RCM cover removed and new relay in hand. So figure $20 total for the job.

I did finally receive the thermal heat tape from eBay. I decided not to use it because it is very thin (ie. not a foam tape) and the bottom of the heat sink is perfectly flat, but the top of the RCM is not, so it wobbled, which is not acceptable.

Thought you all might like some pics:

- The 1st pic shows the new relay soldered in place.
- The 2nd pic shows that you need to leave some air space under the relay.
- The 3rd pic shows that I had to grind off a little bit of the side of the new rivet washer to get it to fit in the corner of the RCM cover. Btw, I removed the old aluminum rivet heads with a hand drill and a sharp 1/2" drill bit.
- The 4th pic shows how the rivet just expands in the base of the RCM (ie. no room for washer in here).
- The 5th pic shows the white heat sink compound spread onto the bottom of an old Pentium II CPU heat sink. The compound is basically zinc metal oxide suspended in silicone (also inexpensive and available at Radio Shack). I'll say I used about as much as the volume of two US quarters stacked two high. So perhaps a 1/32"-1/16" spread on the heat sink.
- The 6th pic shows a side view that illustrates that you have to keep the tie strap's female ends away from the front and bottom of the RCM (or it interferes with the radiator frame or RCM mount)(Btw, I only had 6" tie straps so I had to "chain" them into a longer length).
- The 7th pic shows the RCM bolted down in place.
- The 8th pic shows I used a piece of twist-tie on top of the RCM to make sure that the hood had some clearance when closed. Note that I have permanently removed the plastic "tool bench" cover that used to cover the RCM module (it's now in the trunk because it still shows stuff like the serpentine belt path and emissions hoses hookups).

Hope this helps someone. As usual, I welcome your comments or suggestions.

Regards,
Brcobrem
 

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QUOTE (Brcobrem @ Mar 31 2009, 10:56 AM) index.php?act=findpost&pid=714017
Hi TCCA,I finished the rebuild of the RCM with a new A/C relay. I also attached the heat sink I mentioned previously...I welcome your comments or suggestions.Regards,Brcobrem[/b]
Did you get a chance to test out the new relay(does everything work ok)? I'm considering cracking open my module('93 GL) to see if I can do this, since I'm also having that "fuel pump" issue.
-Chas
 

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Discussion Starter #6
QUOTE (chasmo @ Apr 6 2009, 06:08 PM) index.php?act=findpost&pid=715767
QUOTE (Brcobrem @ Mar 31 2009, 10:56 AM) index.php?act=findpost&pid=714017
Hi TCCA,I finished the rebuild of the RCM with a new A/C relay. I also attached the heat sink I mentioned previously...I welcome your comments or suggestions.Regards,Brcobrem[/b]
Did you get a chance to test out the new relay(does everything work ok)? I'm considering cracking open my module('93 GL) to see if I can do this, since I'm also having that "fuel pump" issue.
-Chas
[/b][/quote]

Hi Chas,

Sorry for the delayed reply. Yes, you are looking at the rebuilt RCM installed and running.

Note that the new blue relay that I installed was specifically for the A/C clutch circuit. I have attached the electrical diagram specific to the 1993 Taurus GL 3.0 Gasoline vehicle. On there you will note the large thin rectangle at the top on the drawing that says "Constant Control Relay Module". That is another name for the RCM (ie. Relay Control Module). Note the little square object called "Fuel Pump / Fuel Gauge Sender".

Looks like you need to determine the exterior connector pin for the Pink/BLK wire, and then (assuming the Inertia Fuel Shutoff Switch has not been tripped by an accident or such), use a simple ohm meter to test for continuity to one pin of the the Inertia relay, then you should find continuity from a different pin out of the Inertial relay that leads to the Fuel Pump relay. That should help you determine which of the black relays are the Fuel Pump relay. If you're lucky, you just simply might notice some burnt surface area, or deformity to the relay from melting, or even the burnt smell of the relay. The A/C clutch relay was like that; it had a bulged-out burnt area on it's nice shiny black surface.

On the top of the relay is an Omron part number (like I mentioned in my original post of 3/12/09). You may get luck by googling like this:
omron "G8SN-UA-007116"
Of course you have to have the the "Fuel Pump / Fuel Gauge Sender" part number, not the A/C Clutch part number that I have used here as an example for you. Don't know if you can contact Omron directly, or, if some an electronics guru could tell you all you need is a standard 12v DC relay with the appropriate size, number of pins and amperage capacity. If you can get the old relay out, you might get lucky by taking it to Radio Shack and seeing what they have that matches up close enough. Also consider that you may just want to take the top off of the RCM, and just take it into Radio Shack and match them up that way (ie. without having to do the de-soldering in advance).

Note that the replacement relay that I soldered in from Radio Shack said 9v DC, and not 12v DC. Even under the higher voltage it's getting, it seems to work just fine and handles the amperage (current draw) ok. Time will tell on that.

Also, I don't expect you to go nuts on this and tie on a heat sink like I did, but you might want to consider not reinstalling that large black plastic shield (ie. I call the "tool bench") that covers the radiator and RCM. Imho, at least the RCM will get better ventilation that way.

Please let me know how it goes for you.

Regards,
Brcobrem

P.S. I was lucky enough to find one brand new (mfg 2004) RCM on eBay that I got for ~$30. It's in the trunk as a spare. Based on past history, I will probaby need to use it some day (ie this is the 3rd RCM this Taurus has seen since birth in 1993). The Ford P/N is F6DZ-12B577-AA .
 

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im also having this "fuel pump issue"... i replaced the fuel pump and filter and it has new plugs n wires...just found out im not gettin any power to the pump and the relay is good. so i traced it back to a blown fuse that keeps blowing on contact almost. the wires trace back to the rcm. my ac hasnt worked and my car makes a pretty bad humming noise. need a new rcm right?
 
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