running hot with AC on only

so i converted my 1997 neon ACR to AC this weekend using all factory parts. retained the origonal ACR radiator, as it was the same size as the AC radiator. also retained the single fan setup, as the factory AC ACR's continued to use that setup.

AC blows cold. everything went fine for about 115 miles. today, i had to pass a moron in a rig on a two lane back road. dropped it into third gear and matted it to pass. backed out about 6k. couple miles down the road, noticed my temp gauge up in the upper third of the range at highweay speeds (60 mph in 5th). shut it down, pulled over, watched the rig gove me the finger. no coolant hit the ground.

figured it was the thermostat. changed that out with a failsafe open after work tonight. didnt chnage anythiong.

the car is only overheating when you put the AC on. it will idle at correct reading for as long as you like, but put the AC on and over the course of a minute the gauge will be into the upper third of the range.

during the swap, car recieved all new belts and hoses, as well as cooling system fluch treatemnt in straight water. car will run hot at either idle or highway speeds. fan operating properly. system building pressure had burped all aor buibbles from cooling system. cleaned out condensor and radiator fins before re install. no oil/water mix

any ideas? doesn seem like an airflow problem, as i dont have the problem with the AC off. id rather diagnose than throw parts at it. as i am not a late model tech (do older cars), im a little at a loss here. in an older car, id figure belt slippage, improper shrouding for mechanical fan, bad gauge, or incorrect air/fuel at idle. with EFI and electric fans, most of these are not an issue i wouldnt think.

so, can anyone shed some light?

michael

Factory A/C systems override the temperature controlled fan and run the fan as long as the compressor is on. Not sure if that is your problem or not.

how could that work? honestly, it would seem to me that the fan running constantly would keep it cooler, not warmer. and teh fan is kicking on with the AC, forgot to mention that.

Excess strain on the engine making it run hot? Either that or the heat from the condenser is heat soaking the radiator. Most vehicles will run hotter with the A/C on.

Do a 60-100 run, pull over, look for leaks.

Does the fan work properly?

I've got an Eagle Talon with A/C. It has two electric fans, one large main fan and a smaller fan on its right. The small fan only runs when the A/C is on. No expert on AC or why it would make the engine run hotter, but I'm guessing the condenser throws heat into the radiator. Most cars I've seen with electric fans and A/C have a switch to automatically kick the fan either on or up once the A/C is activated.

The condenser does throw heat into the radiator - I trick I use to get up to full operating temperature faster actually. It shouldn't create this much difference though, in fact at highway speeds the airflow should be more than enough.

I had the same problem with a 93 Civic I added air to. Couldn't run AC without over heating at idle or highway. 30-45, no problem all day long. I always chalked it up to a smaller no AC factory radiator. Car was t-boned shortly after and never did find the reason.

took the opportunity to clean all debris and dirt from condensor and radiator when i had it apart. my car was a factory heat only car, so i ADDED every part for the AC. factory origonal radiator was AC sixed, si i retained it.

1. still have the under bumper air dam
2. fan works normally without the AC on. on max AC (recirc inside air, full blast cold and fan) the fan and compressor operate continuously.
3. water pump is exhibiting good flow via the eyeball method with the radiator cap off.
4. radiator cap is building pressure
5. coolant bottle not cracked. i actually had taken it out of the car during the conversion to clean it up real good, and did not see any cracks. it will retain fluit until about 1/2 inch above the full hot mark before dumping it outr the overflow tube.

ill try swapping to the spare radiator i have and see if it changes anything. this one is from an AC automatic car (the one i got the rest of the parts from), and has the auto cooler in it, but that shouldnt matter.

anty other ideass? im beginning to suspect that a previous owner put head gasket in a can in it, and when i did the cooling system cleaner it ate it away and is allowing the compression into the cooling system. the coolant recovery tank was bubbling when i pulled over yestyerday, and i have not let it get that hot since, so i dont know if it was a precursor to overheating, or compression leaking through.

again, keep throwingout ideas. im trying to eliminate as many possibilities as possible before determining the motor needs to be gone through. (really, really, REALLY dont want to do that.)

Tired rad. My Miata did this at the 150k mark and it took a new rad to resolve. Flush/boil has low probability of fixing.

My Durango has had the same problem for years. I am planning to add a 2 row radiator and a second fan as soon as I can take it back off dd duties. But I will follow thi s thread with interest until then!

Is this a copper/brass radiator as found on other 90s Chrysler stuff? if so, make sure the fins aren't rotted out.

I'd think of the radiator also. An AC system puts extra strain on both the engine and the cooling system so everything needs to be up to snuff to avoid overheating.

plastic tanks and aluminum core. im hoping that the radiator swap cures it. if it does, ill get one of those 2 core aluminum jobs from ebay to replace it with. just not gonna fight with junkyard parts on this one, as it IS my daily and track car. dont need to be fighting with it...

is there a simple way to test for exhaust in the coolant? like a litmus paper test, or something similar?

Mistakenly wire up the fan backwards? Put greater space between the condensor and radiator?

sachilles wrote: Mistakenly wire up the fan backwards? Put greater space between the condensor and radiator?

i've seen people do this with dodge trucks, apparently in the same years they would have some right hand and some left hand rotating cooling fans. so someone would have a waterpump come apart and tear up the radiator and fan, go buy another one to drop in (or get one out of a yard). seemed so odd to them why it would always get hot when driving around 30-35 mph. was fine at higher speeds or at idle because the air would run backwards or the speed would push it past the fan. lots of frustration with fan clutches too, as they came with both right- and left-hand threads.

ma have found it last night. when i came home from work to start playing with it and try to find the issue, i pulled the radiator cap. saw it was low on coolant again. i had filled it the day before when i replaced the thermostat, and thought i bled it fully. wound up taking most of a gallon. (still running straight water at this point so im not wasting money on antifreeze while diagnosing.) filled it with water, and for giggles fired it up and went for a drive. the needle did fluctuate a biut at first, but stabilized. with the AC on. never got abouve halfway mark on the gauge, and stabilized at the normal 1/3 point. beat the snot out of it just to try to replicate the prigonal condition, and was unable to get it to run hot. even left it idle for an hour with the AC cranked and hood shut, truiong to make it overheat. would not do it. rented a pressure tester for the cooling system this morning before work, and tested it after work. tigntend up a few loose hose claps that appeared at 20PSI. (cap rated at 16, but doing higher for sake of knowing if the head gasket was any good.) let it sit at 23PSI for 1/2 hour, and it never budged. did notice while poking around that there is a 3x5 inch section of fins missing from the fan side of the radiator. didnt notice that when i had it apart, and i guarentee that the radiator is on its way out. so its time to look in ebay fpr a dual pass aluminu job.

So i believe that i had a large air pocket that broke free while passing and came to rst at the coolant temp sensor. i mistook this for bad thermostat. and replaced it. still had the air pocket. so then it led me down this road....

does this sound logical and right to you guys?

Michael

sounds very much like the problem I had with the Suby .... seems to be fine now ... though every month or so I have to add a couple of pints of coolant so there is still a seepage type leak somewhere ... no milkshake look to the dip stick so I'm not too concerned about the head gasket .. just have to remember to check the coolant level every couple of months . actually remind the new owner to do that ... yeah it's gone .. hate to see it leave .. but didn't have room for 5 cars and only need 1 four wheel drive

There is a way to test for combustion gases in the cooling system from a bad head gasket You need one of these kits or something similar.

You put a measured amount oh the chemical in the tester. Place the tester into the radiator neck. Pump the squeeze bulb. This draws vapors, gases, whatever out of the cooling system and the vapors pass through the chemical. If exhaust gases are present the chemical turns from blue to yellow.