'90 coupe overheating

[ice man]

My '90 Reatta coupe began overheating when the AC was on. I checked the fans and the one on the drivers side seemed to be only running on low speed when coolant was above normal. At first I thought it was the fan relay, so I switched the horn  and fan relays and the fan went to high speed and the horn blew?? Now it appears that when the AC is on the fan goes to low speed. Does this make any sense as to what could be wrong? The car is in Florida and I'm in the Buffalo NY area now but leaving soon. I have an '89 parts car here and could take parts down if I knew what may be the problem and what to take. I almost gave Paggett a call last winter while there to get his input, but that's no longer an option.

Any ideas on the problem ?

[Barney Eaton]

As you probably know the fans are controlled by the engine computer.    It get engine temp input and controls the fans.

From a cold start,  there is no fan function until the engine gets to a predetermined temp and then one fan turns on at half speed (believe it is the fan on the engine side) 

If you turn on the A/C the fan in front of the condenser turns on at half speed.     Everything stays in that condition until engine temp gets to around 230  and the computer 

then switches the fans to full speed until the coolant temp drops.     Your problem may not even be a problem if everything is working as above.   

I am attaching a wiring schematic..... it may be for 1990 but I believe '89, 90,  and '91 are all wired the same. 

As a side note....... padgett reprogramed a chip for me several years ago so my fans come on to full speed at a lower temp....  around 215 and the main difference is they make more 

noise but the temp gage does not kick up a couple of notches.  

[2seater]

I have looked at that diagram for years and I cannot see any way the puller fan can run on low speed unless the pusher fan is also running? Maybe I am missing something.

 

If "A" is grounded the pusher fan grounds through the puller fan via relay C and both fans run at low speed in series type operation.

If "B" is grounded alone, the puller fan gets 12v directly and the fan runs on high speed alone.

If "A & B" are grounded, the puller still receives 12v direct and the ground for the pusher is redirected to direct ground via relay C and both fans run at high speed in parallel operation.

[Karlw144]

Your comment starts with overheating with the a/c on. My understanding is that both fans should run on low speed whenever a/c is on. Then as required as a result of increasing coolant temperature, first one fan and then the other should switch to hi speed. By replacing the one low speed relay and the two hi speed relays (all under hood in the control box on the left inner fender) I was able to get the fans on my 90 convertible working correctly. At times one or two bars past top center on the temperature gauge is ok, at least that’s where it peaks on mine, then the hi speed on the fans brings the temperature back to normal. I don’t consider any of this as overheating, just the way it’s designed to work.  But, then again, I could be totally confused🤔🤔.

karl

[ice man]

Karl:

Your description very much mimics the problem I experienced, only my coolant temp was pegging the gauge when standing at a light. After moving again, the temp did come down some and I made it home without being stranded. I opened the hood and as the temperature increased, the fan on the drivers side was again on low speed. As I mentioned in my first post, I swapped the relay from the horn to the fan that wasn't running at high speed and the fan ran on high. The horn also worked after the swap, so I'm thinking the problem is with one of the other relays. I'm pulling all the relays from my parts car and even the ECM and taking them back to Florida with me. Can anyone else recommend parts I should take just in case the relays don't do the trick? It may be some time but I'll post an update as to how I make out.

Thanks to all who posted and helped me understand these cars that are smarter than me.

[EmTee]

Do you have the shop manual?  If like my wife's Allante', there are detailed flow charts outlining the checks to make and resulting repairs.  The relays are a likely culprit and a good place to start, but there are other connections in the system that can cause the observed symptoms.  It's even possible that the fan motor itself has an intermittent issue.  Have you tried powering the fan motor directly through a 20A (or whatever the book says) fuse?  That's one of the Allante' checks I performed when troubleshooting a blower problem.  There could also be a connector or ground issue somewhere in the circuits involved.  The factory shop manual will identify these connections and the location of associated body ground points.

[ice man]

Thanks EmTee for the input. I do have a '90 service manual back in Florida somewhere, but I can't seem to lay my hands on it. I looked for it last winter when this problem started but can't figure out where the hell I put it. I've yanked the ECM and all the relays from my parts car to take back to Florida. I think I may remove and take both fans with me too, as there no use for me here in NY.

[Ronnie]

1 minute ago, ice man said:

I do have a '90 service manual back in Florida somewhere, but I can't seem to lay my hands on it.

Store the service manual somewhere inside the car. When you are broke down on the side of the road you will be glad you did.

[ice man]

It is stored somewhere, I just don't know where? In the car makes too much sense!!!

[Barney Eaton]

Your problem could be just a bad connection at the relay.   Our cars are over 30 years old and most of the connectors throughout the vehicle have never been touched. 

Even in a garage, the cars sees temperature changes,  humidity changes, dirt,and dust.    Whenever I am working on my Reatta and see a connector that might be important, 

I will unplug and replug just to clean the contacts. 

Changing the relay might have simply cleaned the contacts on a good relay.