overheating with A/C on...I'm so confused!

[Buford]

Okay,

Why is it that if I us my 71 2500 GMC with the camper and pulling the boat without the A/C is will not over heat. I've driven that truck all day in the summer and it runs around 190-195 totally loaded. Now, when the truck is not loaded at all, running empty, and I turn on the A/C the temperature will climb up to 215. I usually shut it off by then and it will go down to about 185. I can't imagine the A/C putting on a greater load on the engine than the camper and boat. I am running the A/C cooler in front of the radiator (along with the trans. cooler). Could it be that when the A/C is running the air that is normally cooling the radiator is being heated by the A/C cooler? I don't know, so posting this quandry to you guys.

Thanks!
Aaron

[Palf70Step]

I know AC puts a BIG load on the engine/cooling system, but I would have thought, like you, that the hauling pulling would have strained it more. This will be interesting to see what folks come up with.

[Wrenchbender Ret]

It's not the load on the engine but the heat being put out of the condenser. Go to the car wash & spray out the cond. & radiator. Get down between them. Dirt & leaves get between them & stop the air flow. Sometimes you have to pull the radiator to get it cleaned out good.

[junkman]

I think you have pretty much figured it out. I think the hot condenser in front of the radiator is causing more problems than the increased load on the motor. I've seen a lot of older cars that will overheat, or run much hotter with the a/c on than usual. Most all newer cars with electric fans will either speed up, or kick another one on to compensate for the extra heat and to cool the condenser, something you don't have when using a mech fan. I am not for sure how the a/c works on these truck, I've not had one with functioning a/c, but I think I have read where the compressor is loaded continuously not like the new stuff either. I guess they designed for the stock fan to flow enough when running a/c, but I wondering if they were clutched different for a/c and non a/c, and if your clutch is working properly?

[Buford]

I'll have to check the fan clutch. I wonder if an electric fan would work better than the mechanical fan.

[into69z]

Originally Posted by Buford

I'll have to check the fan clutch. I wonder if an electric fan would work better than the mechanical fan.

Don't mean to hi-jack, but how do you test the fan clutch???

[geezer#99]

It's probably due to the extra heat from the ac cooler in front of the rad. Do you have an ac waterpump on your motor. Bigger impellor in them and they are designed to flow more coolant. Yours could have been changed at some time. Just a thought.

[68gmsee]

Originally Posted by into69z

Don't mean to hi-jack, but how do you test the fan clutch???

Fan clutches stiffen up when hot to decrease fan blade slippage. About all you can do is to check it when cold and then recheck the blade movement when warm or hot to see if it has resistance.

[68gmsee]

Originally Posted by Buford

I'll have to check the fan clutch. I wonder if an electric fan would work better than the mechanical fan.

An electric fan would definitely work better if you get the proper size, but I would first insure that the cooling system is not failing in the truck. Here's what I did on another vehicle with overheating problems.

First, insured that there was absolutely no head gasket or other leaks (leak down test).

Then I made sure the radiator was working at it's max. Had it rodded out and flushed. In your case maybe install a larger radiator if it has only 1 row.

As mentioned above, insured the A/C condenser was clean and free of debris and had a properly working water pump.

Made sure the lower radiator hose was not collapsing under higher engine rpms.

On yours I would also install a radiator overflow tube to insure the radiator stays at the max level of coolant.

[tqlspec]

I'm having the same basic issue but I do have the heavy duty water pump; no coolant leaks. Maybe the radiator is too small.

Any suggestions on a good radiator vendor?

[storm9c1]

Originally Posted by 68gmsee

Fan clutches stiffen up when hot to decrease fan blade slippage. About all you can do is to check it when cold and then recheck the blade movement when warm or hot to see if it has resistance.

Yes, the clutch will stiffen up with heat. However, it is hard to check how much slippage is actually happening. You can't effectively test it by hand with a spin test because once you shut off the engine, the viscous oil immediately begins to flow out of the passages. Another engine start is the only thing that will reset the fluid in the clutch, and it takes a few minutes before all of the fluid is in the right passages again. Once the fluid is there, it can respond to thermal conditions properly.

Service manuals have a "quick" test for fan clutches. If you spin it hard by hand on a cold engine, it should only spin for one revolution or less. If it doesn't spin at all, it's locked (and busted). If it free wheels, then it's also busted. But to test actual activation is tricky. If it roars when the truck/car is really hot (like by 215 it should be roaring at 3000 RPM) then it's working.

There are factors that affect the clutch too! If the fan sits too far back from the rad, not enough heat will be transferred to the clutch. 1" is about the maximum limit. If your fan sits back further, that could be part of the problem and you need a spacer.

Also, not all fan clutches are created equal. In most cases there are 4 types. 1) non thermal - junk!, 2) thermal - ok for most cars, 3) Heavy Duty thermal, 4) Severe Duty thermal

Here is the difference:

1) non-thermal: this is just a viscous clutch, it will only power the fan at about 30-60% engine power. This is useless except to save some fuel economy. Cooling power is pretty lame. Temp does not affect it, but engine RPM does.

2) thermal: these usually have about 60-70% lockup when a certain temp is exceeded (it's a sliding scale starting at 170 degrees). Otherwise when cool, it has about 20-30% lockup.

3) Heavy Duty thermal: this is the best type IMHO. Similar specs to #2 except sliding scale of lockup is more aggressive and they are built better, really good for our trucks.

4) Severe Duty thermal: usually reserved for large rigs, diesels, etc.

Many of these specs were noted from (and can be reviewed at) Hayden's website (one of the largest aftermarket fan clutch manufacturers).

http://www.haydenauto.com/Featured%2...s/Content.aspx


I'm going to present a different view point than all of the others who go with electric fans...... (and mind you I'm a big fan (no pun intended) of electric fans on modern FI vehicles since they are computer controlled, but not so much on older cars/trucks)

If you have no idea of condition, I'd replace your clutch if I were you. Install a HD version, make sure it's 1" (or closer) to your rad, and make sure your fan blades have a 2" pitch or greater. If all of those requirements are met, you cannot beat a mechanical fan in performance. Yes, many believe in electric fans. And many have switched to using them with no problems. But I personally like the simplicity of a good old mechanical fan and clutch. By going with the numbers, 20% when cold seems pretty efficient to me. Not much power or MPG should be lost there. I think people get in trouble when they use flex fans, or no clutch with a stock fan, or the wrong fan blade/clutch in general.

By the way HD clutches need a certain fan blade pitch. Pitch is easy to measure. Set the blade flat on the ground and measure the height of the fan as it rests on the ground. 2" or more is very good for these trucks. Any less and I'd think it's too weak of a fan. If it's a flex fan, ditch it, and get a stock 7-blade fan with a good steep pitch. These fans were used on many cars and trucks from the 1960's through the 1990s!

So a mechanical fan just needs to be implemented and maintained properly and you will be all set.

[Shyguy]

Originally Posted by storm9c1

Yes, the clutch will stiffen up with heat. However, it is hard to check how much slippage is actually happening. You can't effectively test it by hand with a spin test because once you shut off the engine, the viscous oil immediately begins to flow out of the passages. Another engine start is the only thing that will reset the fluid in the clutch, and it takes a few minutes before all of the fluid is in the right passages again. Once the fluid is there, it can respond to thermal conditions properly.

Service manuals have a "quick" test for fan clutches. If you spin it hard by hand on a cold engine, it should only spin for one revolution or less. If it doesn't spin at all, it's locked (and busted). If it free wheels, then it's also busted. But to test actual activation is tricky. If it roars when the truck/car is really hot (like by 215 it should be roaring at 3000 RPM) then it's working.

There are factors that affect the clutch too! If the fan sits too far back from the rad, not enough heat will be transferred to the clutch. 1" is about the maximum limit. If your fan sits back further, that could be part of the problem and you need a spacer.

Also, not all fan clutches are created equal. In most cases there are 4 types. 1) non thermal - junk!, 2) thermal - ok for most cars, 3) Heavy Duty thermal, 4) Severe Duty thermal

Here is the difference:

1) non-thermal: this is just a viscous clutch, it will only power the fan at about 30-60% engine power. This is useless except to save some fuel economy. Cooling power is pretty lame. Temp does not affect it, but engine RPM does.

2) thermal: these usually have about 60-70% lockup when a certain temp is exceeded (it's a sliding scale starting at 170 degrees). Otherwise when cool, it has about 20-30% lockup.

3) Heavy Duty thermal: this is the best type IMHO. Similar specs to #2 except sliding scale of lockup is more aggressive and they are built better, really good for our trucks.

4) Severe Duty thermal: usually reserved for large rigs, diesels, etc.

Many of these specs were noted from (and can be reviewed at) Hayden's website (one of the largest aftermarket fan clutch manufacturers).

http://www.haydenauto.com/Featured%2...s/Content.aspx


I'm going to present a different view point than all of the others who go with electric fans...... (and mind you I'm a big fan (no pun intended) of electric fans on modern FI vehicles since they are computer controlled, but not so much on older cars/trucks)

If you have no idea of condition, I'd replace your clutch if I were you. Install a HD version, make sure it's 1" (or closer) to your rad, and make sure your fan blades have a 2" pitch or greater. If all of those requirements are met, you cannot beat a mechanical fan in performance. Yes, many believe in electric fans. And many have switched to using them with no problems. But I personally like the simplicity of a good old mechanical fan and clutch. By going with the numbers, 20% when cold seems pretty efficient to me. Not much power or MPG should be lost there. I think people get in trouble when they use flex fans, or no clutch with a stock fan, or the wrong fan blade/clutch in general.

By the way HD clutches need a certain fan blade pitch. Pitch is easy to measure. Set the blade flat on the ground and measure the height of the fan as it rests on the ground. 2" or more is very good for these trucks. Any less and I'd think it's too weak of a fan. If it's a flex fan, ditch it, and get a stock 7-blade fan with a good steep pitch. These fans were used on many cars and trucks from the 1960's through the 1990s!

So a mechanical fan just needs to be implemented and maintained properly and you will be all set.

Just to add a little to a great post. A good shroud is also necessary with the fan properly placed in the shroud opening.

[storm9c1]

Originally Posted by Shyguy

Just to add a little to a great post. A good shroud is also necessary with the fan properly placed in the shroud opening.

Oh yes, +1 on that detail as well! Thanks for having my back.

[67ChevyRedneck]

When I added A/C to my truck it overheated badly in traffic. I also have an auto with an additional cooler. I replaced my 3 row radiator with a 4 row and installed a 7 blade clutch fan. Even when it's 95+ outside it will only get up to about 195.

[leddzepp]

Originally Posted by Buford

Okay,

Why is it that if I us my 71 2500 GMC with the camper and pulling the boat without the A/C is will not over heat. I've driven that truck all day in the summer and it runs around 190-195 totally loaded. Now, when the truck is not loaded at all, running empty, and I turn on the A/C the temperature will climb up to 215. I usually shut it off by then and it will go down to about 185. I can't imagine the A/C putting on a greater load on the engine than the camper and boat. I am running the A/C cooler in front of the radiator (along with the trans. cooler). Could it be that when the A/C is running the air that is normally cooling the radiator is being heated by the A/C cooler? I don't know, so posting this quandry to you guys.

Thanks!
Aaron

Your A/C condenser and trans cooler are impeding the airflow to your radiator somewhat....as stated, make sure you have a shroud, this will help direct the air. The increased heat put out by the condenser, and the fact that it has been 105 here are the reason you are overheating. Do you sit in traffic a lot (do I have to ask?....you live in LA) If so, there is little airflow. Do you have factory A/C with the original A6 compressor? It does not cycle on/off and puts a constant load on the engine.

[beautimus]

just to add to the discussion, it might be a good idea to flush and refill your cooling system. If the cooling system is all gunked up, even if everything else is good, it still won't cool efficently. also check/ or replace the cap on the radiator. the cooling system pressurizes to about 10 pounds to raise the boiling point of the coolant above 212 degrees. if the cap doesn't work properly, your efficentiency drops like a rock. just something else to check.
Tony

also since i can't find my spell checker and i am dumb as a rock please forgive my spelling ! lol !

[lazypineapple]

what are your a/c gauges reading?
if the High side is over 300.
thats will cause cooling problems both engine and A/c problems.
since all is well with out a/c on then
ck your a/c presures.
you may need a electric fan on the condenser.or a bigger condenser

does the engine temp do ok running down the freeway?
but climb in slow traffic or idle?.

[Shyguy]

The newer vehicles put a small auxiliary fan in front of the a/c condenser, at the least my '92 K-3500 with 454 did. Even with this auxiliary fan my engine would run hotter than I like when driving slow or at at stop so I put another small electric fan beside it controlled by a toggle switch.

[Buford]

Without A/C, the truck around 180 - 185 on the freeway, maybe hit 190 on large grades. In traffic, it will climb but not too bad...it usually stays around 185 - 190 unless it is 100+ degrees outside, then it will run around 190. I like the small electric fan idea with a toggle switch.

[Buford]

I've been lurking around the internet and what do you think of a pusher fan mounted to the A/C cooler and still us the mechanical fan that pulls? This would help push air through when the A/C is on. I can't imagine it obstructing air more than it pushes.

Thanks

[Buford]

Well, after looking at the truck there isn't enough room on the front side of the A/C cooler for a fan because of the middle support bracket. But behind it there is aobut 3" in open space between the radiator and the A/C cooler. I might mount a fan on the back side of the A/C cooler. I detailed the situation in a pictures.

[leddzepp]

How about 2 smaller electric fans on either side of the condenser?

[Buford]

That might work too, just wire up two smaller separate fans on each side. Thanks.

[piecesparts]

Originally Posted by into69z

Don't mean to hi-jack, but how do you test the fan clutch???

For what it is worth, just replace the fan clutch and be done with it. Testing is fine, but the error factor is too high, just go new and know that you have upgraded the fan.

I have replaced the mechanical fans on my trucks with electric fans. You have to look for a quality fan that is capable of moving the amount of air that would cool your truck and handle the extra load of an A/C system. My input would be to put on a dual fan setup and use a good fan switch that actuates off of the A/C unit and can handle your needs.

[Buford]

Okay, I am now driving a truck with A/C and it's great! I checked the fan clutch and it spun a little loose but the bearing in it was going out, so I pulled it and noticed that it was a non-thermal clutch (which sucks). I replaced it with a thermal clutch and noticed that it was much tighter too. Just took it out on the town, when up some hills, opened her up on the freeway a little, and got stuck in some traffic. On the straights it ran 180 (which I have a 180 thermostate) where is used to run 195. On the hills it ran about 185 and it use to be 200 - 215. In traffic is would run up to 190 usually and the highest it got was 200 sitting for about 5 minutes after a long run. So, I'm very happy with the outcome. Thanks to all for helping me solve this problem!