Air Conditioning and Coolant Temp question

Venompower

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I took the Cobra for a pretty decent drive yesterday, outside temps 86 degrees, and decided on the way back to roll up the windows and turn on the AC. Noticed that my coolant temps which generally sit around 200-205 on a hot day got up to 218. Was nervous about this and shut off the AC and rolled the windows back down. This leads to a few questions...

1. In my main build thread someone mentioned that once the AC is charged, you need to disconnect the battery for like 30 minutes, then reconnect it and let it run 5 minutes no AC and then an additional 5 min with AC on MAX so the PCM can learn to idle with the AC running. I admittedly have not done this since charging the system and if I turn the AC on at idle the rpm's go up and down pretty erratically. Could this coolant temps be caused by the PCM not raising the idle enough, causing the water pump to run slower with the additional load? This happened in town with lots of sitting at stop lights and in traffic?

2. Could this be caused by the system still being on the low side of charged, requiring the compressor to run more frequently that it should?

3. Is this normal and I'm worried for nothing? I researched the coolant temps for the SN95 Cobra and saw a lot of posts saying this is potentially normal especially with AC in stop and go traffic.
 

cobrajeff96

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1) No

2) No

3) Yes

When you get around 230* then it's time to start worrying.

The A/C would not turn on unless the low pressure A/C pressure switch saw adequate charge.

If the idle is erratic, start by diagnosing the Idle Air Control valve, TPS, etc.

The load on the alternator will also inform the PCM about overall system load and the idle will jump accordingly.
 
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Venompower

Venompower

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The idle only gets erratic when the AC is turned on and specifically when the compressor kicks on. The Alternator is brand new, and voltage tests show it working correctly. The TPS measures correctly as well. It's like the PCM is trying to figure out what to do with the extra load.

I'll take it for a drive this week and monitor how high the temps get with AC on, I would ultimately like to see them stabilize even if it's at 220* as I shut the AC off at 216-218*.
 

cobrajeff96

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Yea 220 is A-ok. The 16psi radiator / reservoir cap raises the boiling point of the cooling system. IMO, 220*F is where motors are happiest, you can make more power with a hotter motor.

How erratic is the idle anyways?
 
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Venompower

Venompower

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Yea 220 is A-ok. The 16psi radiator / reservoir cap raises the boiling point of the cooling system. IMO, 220*F is where motors are happiest, you can make more power with a hotter motor.

How erratic is the idle anyways?
You just feel and hear it dip up and down as the compressor cycles on and off.... I was told the steps above were to help the PCM learn to correctly idle. It's probably exasperated by the Procharger and exhaust... whereas in my 4Runner the idle never fluctuates and you could never tell the compressor is on.
 

cobrajeff96

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Old compressor technology as well. And the older the component, the more drag it places on the belt system and thus the motor. It's quite normal for output to surge when a large draw like a compressor comes about. Maybe a vid would help to know if it's excessive or not.
 
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Venompower

Venompower

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Old compressor technology as well. And the older the component, the more drag it places on the belt system and thus the motor. It's quite normal for output to surge when a large draw like a compressor comes about. Maybe a vid would help to know if it's excessive or not.
I'll take a video the next time I move it and post it up.
 

Pallgor

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That’s a tough one. My car coolant is lower with my ac on. I figured because of the second fan. I also switched to a 180 thermostat. My temp was pretty high before I dropped the temperature of my thermostat
 

chithead

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Interesting... just fixed and charged our 98 GT and have noticed this with the hot weather - compressor kicking on really drags the RPMs down, and at idle, A/C is almost non existent. Gets warm, until you're moving again, then the air almost freezes you out of the car. But the engine temp has steadily increased, until it just pegged all the way and boiled over this week. Electric fan has stopped working, and I'm wondering the a bad A/C compressor is the culprit. Ordered a new CCRM, but also a new fan and wiring harness. Thinking about getting a new compressor too while it's all apart down there.
 

chithead

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The blower fan inside the cabin seems to work fine - but does kinda make a noise sometimes, not really a squealing, more like a low howling noise. But the engine cooling fan is what failed.
 

cobrajeff96

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Oh ok, maybe that's it then. The system comes on but soon gets too hot (and overpressurized) and so the A/C high pressure switch trips and kills the system to prevent the A/C compressor from going nuclear and making a huge mess.
 

Maximum95

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This might give you some more peace of mind. In the factory tune on my '95, low speed fan is set to trigger at 213°, high speed fan is set to trigger at 230°. I understand your concern with the temperature, but the motor is definitely designed to run in the 220° range!
 
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Venompower

Venompower

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This might give you some more peace of mind. In the factory tune on my '95, low speed fan is set to trigger at 213°, high speed fan is set to trigger at 230°. I understand your concern with the temperature, but the motor is definitely designed to run in the 220° range!
Does that ring true for all aluminum mod motors? Your 95' has a 302 correct?
 

Maximum95

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Yes my car is a 302. But for the most part, the computer logic is probably similar. As stated above, engines are most efficient around 220°. Manufacturers run engines hotter than we might like, but it helps with emissions systems running efficiently too. Unless your coolant temp is routinely over 230°, I don't think you should worry. I wish I had a real coolant temp gauge on my Mark VIII so I could give you some numbers on it. But I'm sure it runs just as hot.
 

cobrajeff96

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Black Cat Customs can make you new guage cluster overlays so that you can reference the needle to a real team. And Accutach (Mark Olson) did tell me that getting laser accuracy out of the SN95 temp gauge is probably not possible, FWIW. That's the reason I made a mechanical gauge in the engine bay, just in case.

And in my 96 Cobra, the LSpF turns on at 205*F and the high at 210*F. Guess because they figured drivers would be running the piss out of them (and they'd be right in my case!).
 

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Maximum95

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I love that gauge cluster, that's so handy. Thats one thing that bugs about mod motor stuff, the dummy coolant temp. If it's between 180° or 230° the needle just right in the middle.
 

cobrajeff96

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Shouldn't be that way. They are somewhat accurate, not to my liking of course. But the needle should deflect with rises/falls in temp and at least tell a story.
 

Maximum95

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Shouldn't be that way. They are somewhat accurate, not to my liking of course. But the needle should deflect with rises/falls in temp and at least tell a story.
I would have to disagree. I had an '88 Ford truck that would fluctuate as you describe, my '95 GT does as well. It can reflect a wide variety of temperatures. However, all of my mod motor cars are a little more of a dummy gauge. The Mark, Town Car, and '05 Vic that I had would remain in dead in the middle once they warmed up. But, that's just my experience.
 

cobrajeff96

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And that's how it should be. If there's nothing wrong mechanically (thermostat / water pump / coolant flow impedance / etc) or electrically (cooling fan), then your engine temps should stay pretty constant regardless of usage. You should not see wild fluctuations especially in normal driving. Once an engine is warmed up to oeprating temp, there's really no reason (aside from racing) that temps should swing away from where they normally are. But as I said, the temp gauge while you could call it a dummy gauge because it has no actual degree-readings to reference, it does tell a story. Just not a very accurate one.
 

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