Overheating with AC on BUT not off?
 

Hey all,

Figure I'd consult with some of the car wizards to see if I can get some ideas for fixing an overheating issue. I've talked to mechanics in my area and they either don't understand the problem or just make crap up to make them sound intelligent and waste my time and money. First, I did read the sticky on the overheating FAQ but mine is slightly unique.

Location:
Tucson, AZ (so, HOT summers, mildly cold winters)

The Car:
-1988 RS coupe
-Engine 350 w/TBI (stock was 305, swap done professionally before my ownership).
-165 deg thermostat
-Three core radiator nothing fancy
-Dual cooling fans
-Intact Air Dam
-Standard Water pump (NON-high flow) several years old (replace and problem persisted)
-Radiator perfectly clean of debris
-AC system works great and fairly new
-During the summer, both fans are wired ALWAYS 'on'
-During winter, one fan is wired ALWAYS 'on'
-Even setting the fan switch to a low temp wasn't as effective as "always on" solution.

The MAIN Problem:
Car overheats with AC 'ON' but never overheats with it 'off.'

The Symptoms (HOT summer day):
1) Stop and Go Traffic (AC ON) Overheats. At red light I can visually see the temp gauge increasing. Soon as traffic begins to move, it'll drop until the next red light and repeat temp spike. Shut the AC off and it'll drop down to normal (180ish). About 25 minutes of this and the temperature will oscillate up and down (slightly more up than down) til red line at which point the windows go down. Several times its spiked redline and I blast the heater (in the ambient temp of 110deg) to bleed the heat off and it sucks but keeps the car from peaking out.

2) Stop and Go Traffic (AC OFF)...NEVER overheats...The car's coolant temp will run consistently below 220 or around 200 and never climb to redline even at stop lights. (both cooling fans usually running)

3) Highway Traffic at 75mph (AC ON)...will run hot, but never hit redline...it will peak out at 240deg and only fluctuate -10deg if at any.

4) Highway Traffic at 75mph (AC OFF)...will not overheat at all...temp around 185 +/- a few degrees.

5) All driving in winter...NEVER a problem since AC is off.

Here's my line of thinking (please correct or modify if need be):
-All conditions for the AC being turned off does not draw horsepower or put stress on the engine; THUS, the vehicle runs like a champ and normal temps with one fan on.

-However, flip the AC on and its a game changer. Horsepower will drop and a crazy amount of stress is put on the engine hence it overheating from the air compressor requiring power from serpentine belt to run.

(I'm mechanically inclined and this is my best hypothesis).

Short of getting a racing radiator with "4+"core radiator and installing a high flow water pump (I've read Stewart Stage 2 are legit) I'm not sure of the problem. I've even thought of physically (car body) opening up the other side of the air intake in front of the radiator to increase airflow to the opposite side of where the AC condenser (or whatever the square thing attached to the radiator) is. The AC modifying factor has me puzzled and I appreciate the help.

Re: Overheating with AC on BUT not off?
 

Are the fans running with ac on sitting still?

Re: Overheating with AC on BUT not off?
 

AC will heat up ambient air in front of the radiator. This is to be expected. The solution is to configure your fans to run at a lower temperature, thus providing airflow when the car is not moving.

Re: Overheating with AC on BUT not off?
 

Yes, fans are running. I forgot to mention...

-During the summer, both fans are wired ALWAYS 'on'
-During winter, one fan is wired ALWAYS 'on'

I tried setting the fans to turn on at a low temp but hard wiring 'ON' yielded better results. Making the fans turn on at low temp allowed the engine to spike faster and exponentially. With both fans running during summer it slowed the progress.

Re: Overheating with AC on BUT not off?
 

I would think that you might have a coolant flow issue. You also might want to check between the condenser and the radiator to make sure that you don't have a bunch of leaves and whatnot filling the space in between.

I found a lot of debris in there in my GTA, and also set my fans to lower temps. I ended up having to power the fans separately because of the heavy current draw of having them both running for long periods. It ran much cooler after that.

When my radiator started leaking, I replaced it with a two core aluminum, with an additional noticeable improvement.

Re: Overheating with AC on BUT not off?
 

The space your talking about is debris free as is the rest of the radiator.

-You mention a coolant flow problem...think a high flow water pump would aid in lowering the temp? Similar to the Stewart Stage 2 or higher (if they fit)I mentioned previously? I'd probably have to change thermostat and rethink the cooling fans always on or the vehicle will never heat up. lol.

-Did your vehicle have the same AC problem?

-The car currently has a low end cheap non-aluminum two or three core (I'm quite sure 3). Wanted to test to see if it would respond to more cores. It did mildly but with the AC on it's uncontrolled heating.

Re: Overheating with AC on BUT not off?
 

I had lots of problems with engine temp while running AC at idle. The aluminum radiators are better at dissipating heat. That's why the stock replacement is just a single core. Mine is a two core (I have a stock 305 TPI). They also have three core aluminum ones.

As far as flow is concerned, it could be a blockage somewhere. I would think that even a stock water pump should be able to provide sufficient flow as long as everything else is good.

From your previous posts, I would say that your engine is running much hotter than I would like. Mine was up there, too before I reconfigured the fans and changed the radiator. I am still running a 195 degree thermostat, but the engine never seems to run hotter than that.

Re: Overheating with AC on BUT not off?
 

im not sure if i overlooked this or not, but how are you able to tell the motor is overheating?

is the coolant bubbling? did you use an inferred thermometer? are you reading from a stock or aftermarket gauge?

Re: Overheating with AC on BUT not off?
 

Temperature is my main concern as well and I do not like the high temps as I do not want to burn the engine out faster than normal circumstances should dictate. Again, only when the AC is on though.

I haven't ruled the blockage out but considering the overheating problem is unique to the AC on and not off, and having replaced the radiator, water pump, hoses, thermostat, it leaves little left to replace.

-Perhaps it's time to replace the radiator with a Aluminum 3 core, high flow water pump, higher thermostat and rethink the constant on dual fans.

Maybe the ultimate question is how to dissipate the heat more efficiently with the AC running given the engine was a sizable increase from the 305 to 350. The engine was not a 1980's 350, I had a stock 1992 Chevrolet 2Dr Blazer that had the exact engine, TBI, and it ran perfect but it had a pully fan instead of dual electrics. No problem overheating regardless of AC on/off.

Had the car for 8 years and the prior owner had the same problem and didn't drive hardly. lol

If somebody has an "Ah hah" moment...I'd sure like to hear it.

Re: Overheating with AC on BUT not off?
 

I'm able to tell because of several things.

-(running the AC during hot summer day) My fiance forgot about the problem one summer day and blew the cap off the radiator and just prior heard a roaring bubbling then, "poof"
-Temp guage (may not be accurate to the degree but generally accurate)
-When the temp according to the instrument cluster reaches almost redline, you can audible the bubbling and feel the insane heat off the engine.
-Again, temp gauge indicates overheating and the mild fumes of heated gasoline (this one is hard to describe)
-I've never driven a car that after driving for a while ac on/off, you open the hood and immediately are like, "that too hot...that ridiculously hot"

Probably the most accurate:
-I bought an OBD reader cable to plug into my laptop with a computer program and recorded a typical drive...that was crazy fun but also made me realize the cluster gauge and my ears on not playing tricks on me.

Re: Overheating with AC on BUT not off?
 

gotcha, bubbling is all i needed to hear

most of the stock temp gauges i have used are always way off, mine will read full hot when its running around 200 +/- 10, i chased my "overheating" demon for a week(replaced everything except the radiator) before i listened to other members telling me it was just my gauge.

but your issue truly sounds like a real problem

Re: Overheating with AC on BUT not off?
 

on that note, has the radiator cap been replaced?

Re: Overheating with AC on BUT not off?
 

Radiator Cap replaced, Yes, but problem has a longer history than that incident.

Yeah...it's a real problem in the summer with AC but that's where the complaints/problems/gremlins/demons end. In the AZ winter...its a phenomenal car. Tracked mpg on a roadtrip with my bro 36 mpg from El Paso to Ft. Stockton no AC and 22 in town with no AC. I ran the numbers over and over because I didn't believe it either..on the way back from TX we got the same results. It's a freaky car. Good and Bad.

Re: Overheating with AC on BUT not off?
 

I am in Tucson as well. I have replaced pretty everything for the cooling system, and the car still runs hot. I have realized that these cars were not made for really hot climates. So, I am pretty much doing everything I can to help it out. I know exactly what you mean about the heated gas fume smell, all summer long the wife is yelling at me "your car smells". I have the constantly running dual fans (thanks to PO).

Changed out the radiator (because mine was leaking). Put in a 180 Tstat, which helps a little. Im currently in the process of getting parts together for the Taurus fan mod. Eventually will upgrade to a 2 core radiator. Also changed out the starter due to severe heat soak issues.

If you go the Pull a Part on Michigan Ave right behind DM off of Golf links And Ajo, they have a boat load of Tauruses (Tauri?) and Contours to pull fans from.

What part of town you live in?

Re: Overheating with AC on BUT not off?
 

Is Waterpum Good? Does OverflowTank Have Leak Or Cap Does Not Deal Well. If U Flushed System Did Get Air Trapped/Burp Coolant System, Hoses good, It Sounds Like A Blockage, Best OfLuck

Re: Overheating with AC on BUT not off?
 

Veaceonee: I know exactly what/where your talking about. I'm sort of East Side. I'll look into the mod.

Lakerman62: Water pump is good, fans are good, hoses are good, system burped. I would generally agree with the consensus of a blockage but it doesn't make ANY sense that the car runs absolutely perfect until the AC system is turned on THEN the gremlins come out to play. If it were a blockage it wouldn't matter with the AC on/off, the car would overheat regardless.

Here's maybe where my line of thinking is going. The engine cooling system is fine, hence it operates perfect with the AC system OFF. We're on the topic of a blockage potentially, would the AC condenser on the radiator (which is suppose to release heat and be cooled by the airflow over the radiator), IF blocked create the symptoms? What would make the condenser be excessively hot and overwhelm the engine coolant radiator and not dissipate the heat efficiently (reminder, no debris is present)?

Realistically the condenser is a mini radiator for the AC system. You can buy radiators to increase the cooling of an Engine by increasing the row or changing the material, can you upgrade the AC condenser 'radiator' to allow more airflow through a different material or rows? Larger, more rows? Just a thought.

Re: Overheating with AC on BUT not off?
 

Do me a favor. Hook up some A/C manifold gauges to the car and start it up during the heat of the afternoon. Let it idle and monitor what the low and high sides read on the gauges as well as what the coolant temperature is.

Arizona is hot enough in the summer that even with the A/C turned off, any type of cooling system deficiency would be easily noticed. So I would probably rule out hoses, water pump, thermostat etc.

My theory is that there is an air conditioning issue. Could be a clogged line. Could be the condenser. Just because there are no leaves or dirt visible between the condenser and radiator doesn't mean that the condenser itself isn't caked with dirt inside the fins.

Arizona is a high use A/C climate. It could have had a compressor go in the past and was replaced without flushing. It could be a plugged orifice tube. The desiccant bag could have broken. It could have been filled with refrigerant without a proper vacuum. Without a good vacuum, you get air in the system. Air doesn't compress very easily and as such sends the high side pressure through the roof. High high-side pressure readings will send a mammoth amount of heat to the condenser, which of course sends that to the radiator.

Re: Overheating with AC on BUT not off?
 

:yup: :iagree:

listen to what he is telling you your basic cooling system is fine. except that a aluminum radiator is more efficient. I teach collage level basic refrigeration I have spent a lot of time in the Arizona heat and I lived in Texas for several years the condenser adds a LOT of additional heat in front of the radiator.. Sand-dirt gets stuck between the fins of the condenser the only way to tell is try and shine a light though the fins you will be amazed how much garbage is stuck right where the fans are. is your car using R-12 or R-134a or something else is the condenser original equipment or has it been replaced with an updated design our original condenser are Tube and fin not very efficient replacement parallel cross flow condensers work much better at removing heat !!! That said I have had this same problem very bad !! look at my sig I have a very modded 358 sbc sniffing nitrous and very cold A/C using R-401 refrigerant. I have the stock radiator and condenser original to the car. and converted to dual fans same as you it would work great on its own.Turn the A/C on not so much...!! my secret weapon was to add a additional pusher fan in front of condenser that only comes on with A/C or manual override now 210 degrees engine temp. 36 degrees a/c duct temp on 102deg day idling for over 30 min in traffic ... the F%*D taurus fan swap should in effect do the same thing more air flow however you must check total integrity of the A/C system first !!

Re: Overheating with AC on BUT not off?
 

I'm having the exact same issues as the OP. Car runs fine temp wise until I turn on the AC in traffic. On the highway no issues. In stop and go the temp gradually climbs until I boil over into the overflow. Turn the AC off and poof, runs fine.

I am running a BeCool aluminum radiator with the single electric fan. I'm going to do a dual fan swap this winter but I think this pusher fan idea has some Merit, never would have thought of it on my own.

Re: Overheating with AC on BUT not off?
 

:thanks:

thanks it works phenomenally.. before doing this MOD A/C and low speed driving where not an option for me !!! :driving:

Re: Overheating with AC on BUT not off?
 

What fan did you wind up using?

Re: Overheating with AC on BUT not off?
 

this is my pusher fan set up I found this fan on a V8 converted S-10 I used to own...

I connected to the factory single fan wire harness so is turns on with the A/C the wire that used to go to head temperature sending unit now my manual over ride for pusher fan... Fans one and two are controlled by a separate fan controller that has a thermistor installed in the radiator core runs fan one& two simultaneously :thanks:

Re: Overheating with AC on BUT not off?
 

What did you use to hold it into the front of the car? Nylon zip ties?

Re: Overheating with AC on BUT not off?
 

Napa sells a electric fan replacement kit that has the long push through ties and rubber isolators some people don't like using them because you can damage the radiator core if you are not careful or it is in week condition

Re: Overheating with AC on BUT not off?
 

What fan do you use as the pusher?

Re: Overheating with AC on BUT not off?
 

try something like this ...


http://www.summitracing.com/parts/mar-m103k


:totopic:

Re: Overheating with AC on BUT not off?
 

Yes, back to the topic.

There was a post I read here where an individual took apart his dash to close the air vent in the dash that lets fresh air in all the time. He said that worked wonders in keeping his AC cold because it stopped mixing the cold air with the hot air coming in from the engine bay.

Re: Overheating with AC on BUT not off?
 

this x 1000

I had this exact issue, could not figure it out and I tried and tried! the space between the condenser and radiator was clean I pulled them both out, they looked pretty much clean also

I build the turbo setup on my car and painted the engine bay. When I had the radiator and condenser out, i CAREFULLY pressure washed it making sure not to knock the fins over. you would not believe the amount of dirt/crud that came out of both! the car ran SO much cooler afterwards it was insane

so what I'm saying is, pull the radiator and condenser, take them to a car wash and engine decease and blast um out. it'll cost $20 including new antifreeze, worst thing that happens is you have a cleaner car and can eliminate that as your issue.

Re: Overheating with AC on BUT not off?
 

I have a 1991 camaro 305 TBI, it overheats with a/c on or driving on steep hills. I've done almost everything except stronger water pump. I believe it might be that the engine is running lean. I did some mods and never tuned it. I've done some research and this is my opinion:
With the a/c off the cooling system is enough to evercome the extra heat generated by running lean. Once the a/c is on or, driving on hills, the engine generates more resistance which under normal air fuel ratio will generates mor heat, but by running lean the cooling system can't handle the heat.
I am still deciding convert it to carburetor or put in a MicroSquirt computer to fix the lean problems.
I did some test with a wide band o2 sensor and the a/f ratio was around 16 and 17
Let me know what do you guys think.

Re: Overheating with AC on BUT not off?
 

Do you have a single fan or dual fans? Is your air-dam intact?

On a single fan car, this is a common issue as they get older. On my 84 carbed car I had this issued, upgraded to an LS dual fan and never looked back.

Re: Overheating with AC on BUT not off?
 

I have a dual fan and the air-dam is not intact but in good conditions.
If I am in traffic with a/c on and it starts to overheat, temperature starts dropping when I turn off the a/c without the car moving.

Re: Overheating with AC on BUT not off?
 

That's the issue as the cars get older. Flush the system, clean out the radiator and make sure there is no debris between the condenser and the radiator, use water wetter, make sure your cap is still good and if that doesn't work, upgrade to dual LS fans.

Re: Overheating with AC on BUT not off?
 

How are your fans setup?

Are they LS1 fans but with stock dual fan wiring? Do they both go on?

Another thing to consider is maybe try checking your temp sender...maybe it works at certain tems, but goes over at a cetain temp...the one in my camry did that...it would read fine, then skyrocket with the ac on. I had to replace the sender and it worked fine.