First, I want to say that this forum has been incredibly helpful for me. I bought a 1985 about a year ago, and there have been a couple of things I had to fix. This forum has given me the confidence to repair a number of things that would have cost me hundreds (lots of them) of dollars. I am 62 and I used to be able to work on cars when I was young, but the technology has passed me by.

I have tried to find threads that would answer my questions below, but there are so many that when I use the search I end up spending hours reading all of the interesting threads, even though they aren't what I am looking for. I am easily distracted, and the information and threads are so danged interesting.

My car overheated when I got it, and I found that the fuse on line to the relay was fried. Also, I was told that the BCM was not signaling the main fan to turn on. I live in El Paso, so I told the mechanic to just wire the fan to run when the engine is on.

That worked OK.

But, I am very leery of the 225 degree supposed normal running temperature.

If I turn on my A/C the temperature gets up in the 210-15 range, and when I was traveling down the highway and turned it to high a/c it went up into the 230 mark so I shut it off.

The other day I turned on the a/c as I started the car-Lo temperature, and looked to see if the A/C condenser fan had started. It hadn't.

Short story that I have made long, is the a/c fan supposed to come on when the a/c is turned on? And, should I be freaking out when the temperature reaches 230-35 driving around? One last question. Should fan(s) run after turning the engine off to cool it down?

 

With the fan running all the time the temp should be in the 195-215 range. It shouldn't get up to 230 when you're moving. Does it get hotter the faster you go? That would indicate a restriction in coolent flow. Either the thermostat isn't fully openning or the radiator is partially plugged.

 

When I'm driving around town, without the A/C turned on, it runs around 195-200, maybe up to 201 or 202 it sitting at a light. Then it comes back down to the upper 190's as I drive a bit.

Driving for hours at 80 mph w/o air conditioning it was at about 200 degrees.

It is only when I turn on the air conditioning that teh temperature goes up. With it set on normal the temperature goes up to around 215, and with it on high it got up to 231, so I turned the air conditioning off. I have read that the condensor fan should come on at 225 (I think) and I have also read that it should come on as soon as you trun the a/c on.

I'm beginning to think that my a/c condensor fan is not turning on.

 

Fan should be on at around 230 psi and off at about 190; ie to maintain average head pressure of 200 psi. You need a manifold gage set to check it out. ECM is sending voltage to a switch on the high line which opens at the 230 psi threshold causing a voltage rise at the ECM. It then grounds the Main Fan Relay. Disconnecting the switch simulates the open and should turn on the Fan. I'm going to guess that if you do this, the fan will come on. since you've got a fan with the a/c off. If not, the reference wire is shorted to ground or the ECM is shot. Otherwise, it's either too cold (much below 50 degrees) for pressure to reach the threshold; or the compressor is pooped out and can't make pressure; or the system is low on gas; or it's a faulty switch (and if it's a faulty switch or the reference shorted to ground, the system is either spewing gas or the high side limit is kicking it off to keep it intact). Once you know what the pressures are, you can figure it out.

 

Thank you both for the quick responses.

SunCR, you switched to psi and lost me really quickly.

Is the condensor fan operation determined by the psi of the a/c system, or the temperature of the car's engine cooling system?

 

PSI of the a/c system controls the main fan when the a/c is on. You can convert PSI to temperature. For example, R12, at a pressure of 200 psi, has a temperature of 138 degrees. Realistically, what's flowing through the condenser has subcooled, so it's temperature is about 125 degrees (to determine the amount of subcooling, obtain the pressure and then temperature at the Condenser outlet - though auto a/c guys rarely pay any attention to anything other than pressure). The design is to maintain that temperature, and the ECM accomplishes that by cycling the fan. The car's coolant temperature is maintained by the thermostat and it will be at a lower temperature than it would be without the a/c because the fan is coming on sooner and staying on longer. If yours isn't working that way (and because the fan isn't coming on with the compressor engaged) you need to look at your system's operating pressures first and with that info, it's usually pretty easy to figure out.

 

Couple things to know before going further...

The front fan is NOT for a/c. That is the HD cooling accessory fan and does not come on until 238...its the last chance fan...

The a/c should trip the rear fan almost as soon as the a/c runs. head pressure does this.

Normal fan on is 228 unless a/c is turned on, then its immediate.

There is most likely a bunch of trash stuck between the radiator and condensor that you cannot access or even see. You MUST remove the top shroud to even see it. Clean that out, it'll help.
If the condensor is getting beat up and dirty, it blocks air to the radiator. As the condensor gets too hot, it blows that heat directly to the radiator and makes things worse.

230 with a/c when its 90+ outside in traffic is normal. When rolling the temp should be down to 200-210 with ambient of 90-100 degrees.

The REAL cure....spend $250 on a new all aluminum double row radiator and $75 on a new condensor.
That will drop the temps 20+ degrees under ALL conditions.

These things are made to run hot. Too hot...no room for error at 230...Much more comfortable when things run at 195.

 

Thanks for the info and clearing things up for me.

I made the mistake of trying to pull the air cleaner part that is over the shroud off, and one of the bolts that holds it down fell down between the two radiators, I had to remove the shroud to retieve it. I did find lots of crap down there and cleaned it all out.

I guess that having my engine overheat when I first got it, and reading about normal operating temperatures around 225 just has me pretty jumpy about getting the temperature up to 231-2 with the a/c on high. I am much more comfortable when the temperature is around 200.

Just so that I am clear, the front fan should not come on unless the temperature is in the mid to upper 230's?

That just scares me.

Thanks guys for all of the help.

 

Per Chevy's Bulletin, the Aux Fan started out as Dealer installed option in '85 when autocrosser's and high altitude users complained of overheating. It was subsequently a Factory Option. Realistically, if it's clean, it should never come on and plenty of Vettes left the Factory without it.

As to replacing the Radiator and Condenser - stock (HD option which the last time I looked was all that was available) works for me, but it's probably a matter of price. You have a fan problem though that needs to be figured out first.

 

First, it sounds like you should break out the pad and pencil.
there are a few things you need to know.
A. the computer grounds things and the power should be at the accessories with the computer grounding the circuit to make it work. This way, if there is a short, the computer does not get fried.
B. almost everything works off of relays, and fuses. if the fuse is good, the power goes to the relay and stops. Then the power is delivered to the accessory if the computer grounds the negative side of the relay coil (because it already has power).
1. turn the key on and start the engine without the air on.
A. the fan should come on when the temp reaches 232 degrees and shut off at 215.
(I have an 86 and it happens this way)
2. let it do this a couple times to determine that it is repeatable.
If you get to 240, back the car out and drive it with the air off till the temp comes down. your engine is greatly dependent on air flow.
3. let the engine cool to about 160 degrees. start the engine and note that the fan is not on. turn on the A/C and note that the fan comes on immediately.
If it doesn't, shut it off and start checking things with an ohm/volt meter.
4. there is a high pressure switch and a low pressure switch adjacent to the right exhaust on the frame.
If the high pressure switch is tripped, you should have a fan signal to the computer and the compressor will not have any power.
You will have a fan relay coil power and ground, and fan power. you can check the fan power at the connector at the fan.
If the low pressure switch is tripped, the compressor will have power, but it will cycle if the compressor is turning and there is low freon in the system.

(The computer is an optimist and keeps checking to see that someone will put freon in the air conditioning system.)

If you have too much head pressure (high pressure switch) the compressor will shut off, and the fan will cool the freon, and the pressure will drop, and the compressor relay will energize and the compressor will come back on.
You will know that there is not enough airflow when you are sitting at a red light and suddenly you notice that you are sitting in a warm car and cold air has ceased to flow out.
of the vents.

Just a note,
I drilled those crummy air filter stud/anchors with a 1/8" drill bit on each end and pop rivedted them to the fan shroud. Now they are always where they need to be and don't rotate if I turn the ***** too tight.

In addition, I wired the aux fan relay coil to the power wire on the main fan so that when the main fan comes on, the little fan runs at the same time. In Phoenix, at 115 degrees, you need all the help you can get.
The aux fan just wasn't coming on soon enough, and staying on too long, so I had the computer turn it on instead of the sender . It also helps the air conditioner in that it cools the freon in the condenser and keeps me cooler as well. Keeps those pesky high pressures away because with the air on, in traffic, the fan is on until i get going, not just when the engine is hot.
Just as a side note, I put a double row aluminum radiator in the car (yours is a one row) and on the freeway in 115 degrees, the engine temp is 185, and 205 in traffic.
I also use a 160 thermostat. but that is another debate.

 

Wow! That is a lot for me to digest. Like I said, I have the main fan wired to run when the ignition is turned on.

I may have to look into wiring the auxilliary fan to the main fan wiring. I don't know. I like to keep things as they were designed from the factory, so I may have a new chip put in. I was told that the chip wasn't turning on the main fan when it should, and that was why the fan was set up to run all of the time. There may not be as much of a problem as I think. It may be that I just get freaked out when the temperature climbs to past 230.

Thanks, again, to all of you for your help. As I said, the people on this forum have really helped me to get back in and fix things myself after 30 years of just leaving my car with a mechanic. Now that I am retired and on a very limited income, saving a couple of hundred bucks by doing the work myself is a big deal.

 

Assuming you've check this, but you have made sure that your radiator is clear of debris...the design of the C4 has a bad habit of making the radiator act like a vacuum cleaner. It's amazing how much crap can get caught in the front of the radiator.

http://forums.corvetteforum.com/c4-t...mperature.html

 

I have noticed that. So I have begun making regular checks of that. Maybe I should consider hiring out as a parking lot sweeper.

 

As you know I am new to corvettes, have 92 LT1 automatic 80K miles. question/concern is took it out in 75 degree sunny day in the city to work, digital temp got to 230 degrees at stop lights and came down while driving. normal digital running temps seem to be 209-215 degrees at 50mph. 1st fan comes on at 227 degrees idling in driveway and both fans are on when a/c is running -never got hot enough to start 2nd fan.
Normal or running too hot?? - I also just cleaned the front of the radiator as suggested by the forum members

thanks for the help

 

Did you remove the radiator top shroud? if you are just looking in the nose toward the radiator, you're NOT seeing the problem.
Trash gets blown around the condensor (that you see) and stuck between the radiator and condensor. It cannot be seen from anywhere under, in front or looking down or in the area....the shroud must come off.

This is an annual maint issue or whenever odd hi-temps are seen. I have found dead birds, trash bags, news papers, hair, coke cups, and all other form of garbage that you see on the side of the road.

 

went in through access hole on right side of shroud with brush then hose and stuck hose through the fan shrouds. have to spend more time finding all the screws and bolts for the shroud (they never seem to end)