A/C works in the afternoon, but not in the morning...

[GT40XStang9]

Setting: Houston TX

Car: '88 Mustang GT, factory air conditioning, replaced a/c clutch about 1 year ago

Symptoms: Turn on car in morning (7:30am) for 14 minute drive to work, a/c blows, but clutch doesn't engage so it never cools off entire duration of commute. Leave work @ 5:30/6:30pm and a/c cools immediately.

Notes: Low side pressure is at 45psi when a/c is functioning. Vacuum lines all in one piece, no broken distribution trees, etc. If temperature was to blame, the underhood temps should be close the exact same when arriving to work in the morning as leaving for work in afternoon (or driving home). Also, I can pretty much turn on car at any time in the evening and the a/c will work properly.

Possibilities: WOT relay may be culprit, but I have never experienced nor heard of anyone else experiencing this before.

Any ideas/questions? Thanks in advance.

BJW

 

[90mustangGT]

What's the high side reading? How much is in the system?

 

[GT40XStang9]

...high side checked 200psi

 

[90mustangGT]

...high side checked 200psi

Good reading, not engauging, check to see if your clutch is getting power?

 

[PuterAmI]

On Foxes, it is common for the wiring to the WOT relay to melt the insulation. Check and repair. Then, if you are getting voltage to the switch but not past it with 45PSI, replace the switch. I have had the relay wiring make the switch go out intermittently. Also, I have another switch that would make the compressor clutch oscillate.

 

[GT40XStang9]

Update (I know it's been a while):

+12V is getting through the pressure switch, which can also be measured at the WOT relay. The problem is that the +12V is only upstream of the relay (red trigger wire). I get no reading downstream of the relay (orange/light blue trigger wire) which means it won't kick the compressor on.

If I run the car for a while (10-20 minutes) or the weather is hot, the relay functions correctly, power moves through the relay coil and the clutch kicks on. I don't understand how this could happen on both the original Ford relay as well as the newly purchased relay from the autoparts store.

I plan on switching relays with another 5.0 to see if the problem clears. Is there any chance that the relay is seeing +12V but not enough current to charge the coil? If this is the case, it must be because of another issue?

 

[PuterAmI]

I take it that the wires at the relay all looked good?
Is it that you don't have 12V at the relay when cold and do have it when warm?
How good is the signal to trigger it before/after?

I am suspecting that you have a dirty connection or damaged wire.

 

[04sleeper]

I am suspecting that you have a dirty connection or damaged wire.

Here is a picture of what my wiring for my A/C realy plug looked like until I fixed it.
View attachment 504227

 

[GT40XStang9]

12V upstream when warm OR cold.

0V downstream when cold.
12V downstream when warm (A/C works).

89Sleeper, how did you 'fix' the wiring? I guess my only option is going to a pick-n-pull until I find another relay connector w/ decent wiring.

Thanks for the help Gents!

 

[04sleeper]

89Sleeper, how did you 'fix' the wiring? I guess my only option is going to a pick-n-pull until I find another relay connector w/ decent wiring.

Thanks for the help Gents!

No. Actually I cut about 6 to 8 inches off the wire to get back to where it was good. Then I carefully used a small pick to release each terminal inside of the plug, making sure to mark where each wire came from and took a picture of it to give me a reference.

Once I did that I used and old tupperware bowl with some "Purple" degreaser and water and put it in the microwave until it was boiling. Then I dipped the plug into it several times and scrubbed it with some pipe cleaners and a small brush until I got it clean. (Which worked like a charm!)

Then I used my soldering gun and some small screwdrivers and pliers to slavage the old terminals.

Then I soldered the terminals back onto the wiring harness where I had trimmed it back and snapped them back into place on the plug and put some dielectric grease on the connection and plugged in a new relay.

It worked perfect and never gave me trouble after that.

Hope this helps.

Good Luck.

 

[GT40XStang9]

Spliced it, soldered it, insulated it, and put it back together.


...Still doesn't work.

 

[PuterAmI]

Very, very strange. And you are getting a signal from circuit 73 O/LB when cold? Compare it between not working and working to see if there is a difference. Also, can you jumper the WOT relay and have it work when cold?

How about grounds? Have you checked them all?​

 

[GT40XStang9]

Very, very strange. And you are getting a signal from circuit 73 O/LB when cold? Compare it between not working and working to see if there is a difference. Also, can you jumper the WOT relay and have it work when cold?

How about grounds? Have you checked them all?​

I am getting 12V from circuit 361 R and 0V from circuit 73 O/LB when cold.

I am getting 12V from both when warm. Now I'm confused about which direction the signal for the relay is coming from. Does the current come from circuit 71 or 361?

I can jumper the relay to activate the compressor. I'm thinking about wiring a high current manual switch to do this from inside the car.

 

[PuterAmI]

I am getting 12V from circuit 361 R and 0V from circuit 73 O/LB when cold.

I am getting 12V from both when warm. Now I'm confused about which direction the signal for the relay is coming from. Does the current come from circuit 71 or 361?

I can jumper the relay to activate the compressor. I'm thinking about wiring a high current manual switch to do this from inside the car.

I can always check my 88/89 this weekend to see what I see. I am not positive what to expect. I would just have to take a look at my shop manual and see what it says about these circuits and experiment a little.

Since that is the trigger for the relay, I would not think that it needs to be high current. Your high current side would be the other (883 and 347 for the field coil). Of course, by wiring the switch, the only thing you would lose is the WOT cutout. But, most folks don't care about this. I know I didn't on my 84 when I changed out carburetors.

 

[GT40XStang9]

I'm pretty sure that I am the most disgruntled commuter in the Houston metroplex, every morning.

 

[04sleeper]

Hmmmm. Don't give up now. It sounds like you are tracking it down. Might just be something simple like a new switch.

Hope you find it so you are not too disgruntled. Road Rage is not good.

JK/