ujmolter

Help please!

1988 Convertable with one cooling fan.

Let me set up the situation I had with my cooling system. My car is idling with the AC running and it is a 90 degree day. I am outside of the car in my garage and the hood is up. (Trying to fix the cruise control) Everything was working fine (except the cruise control) UNTIL car overheats. Don't notice it till I hear a loud pop and the coolant reservoir cap blows off and radiator fluid is everywhere. I run around in the car and notice the temp is at 280 and the radiator fan in not running. AC compressor is cycling on and off about every 3 secs and no cool air is coming out of the vents. I shut the vehicle off thinking what is going on?

I let the car sit for 30 minutes then check the temperature of the coolant (back down around 235) and decide to crank it up to see if the problem occurs again. To my surprise the fans back on the AC compressor is cycling normally and cold air is coming back out of the vents. Only difference...check engine light on.

I let it idle and everything seem normal and the temperature hovers up to around 250. I take it for a short drive and as advertise the temperature stays between 195 and 225. Pretty normal.

I decide to take it to the local mechanic and explain to him what is going on and he checks it out. He replaced the thermostat and checked the Ohms at the fan connection and everything checks out. Check engine light no longer on. He did not disconnect the battery to extinguished the light.

He ran the car at idle for over an hour with the temperature around 225-230.

I picked it up today and everything was fine till I pulled into my driveway and put it into park. First thing I noticed was that the AC was beginning to blow warm air. Coolant temperature was back up to 235 (fairly rapidly) so I pop the hood and fan was not running (suppose to come on around 228 or so). AC was cycling again. I shut the car off and then immediately restarted it and everything was back to normal. Fan and AC working fine again.

I called the mechanic and we discussed the issue and he had told me that he did not have an OBD for the vette but in his opinion with the way the issue came up again, he thought it could be the computer control module.

Anyone else experience anything like this?

antfarmer2

Check your freon might be a bit low. A check your vacumme line to your brake pedal to your pod just replaced mine felt like a dead worm.

ujmolter

AC just serviced and leaked checked. Brakes work good. Don't think it is either. Thanks for the suggestion.

crowz

Cooling fan relay is on the way out or bad ground. The reason Im saying this is because with the a/c on the fan should run all the time. If its was JUST the a/c not keeping the fan on Id suggest a problem there but since it over heated AND didn't have the fan on all the time with the a/c that narrows it down to the relay, the fan or power/ground of the relay. Odds are high its the relay. Easiest way to test it is to probe the wires at the relay when its messing up aka fan isn't on and the a/c is on. That way you can determine if power or ground is missing or if they aren't then it would be a bad fan motor itself.

crowz

Also no matter what anyone says relays can become intermittent. They don't always just die completely.

antfarmer2

The vacumme line to the brake switch has nothing to do with the brakes working good but will keep your cc from working. And agree with Crowz with the relays and bad connections.

ujmolter

Ok thanks. I will look into the relay issue. Question: will that relay have anything to do with the AC compressor cycling on and off when the fan quits working?

ujmolter

Oh and also, where is the relay physically located?

crowz

The a/c cycles based on pressure in the lines. When the fan stops the a/c will start doing that because the line pressure is out of whack from the fan not pulling air across the condenser.

So yes that normal. Id ignore the a/c as a symptom since it just responding to being to hot from the fan not pulling air. The core problem is the fan not coming on.

crowz

The fan relays on an '88 Vette are located as follows:
main fan - rear of left inner fender well, below the brake master cylinder
aux fan - upper left of radiator shroud, near upper hose

ujmolter

I only have one fan. so I am assuming it is the relay below the brake master cylinder. Am I right?

crowz

Yep.

ujmolter

Ok. Thanks. I will give it a go. It will be a few days but I will hopefully have some positive results. Oh one other question..will the check engine light coming on somehow be associated with the intermittent failure of the cooling fan relay? The engine check light was intermittent also.

crowz

Anytime the check engine light comes on you need to pull the codes. That's what its there for.

Since an 88 has obd1 theres no reason for not pulling the codes since you can use a paper clip to get it to flash out the codes to you. Google how to do it and the codes meanings.

antfarmer2

There was another member that had silver crud on thier fuses that caused problems try cleaning those as well and any connections and grounds. what codes are you getting now

Mtn Billy

You don't have a fan in front of the radiator? It would blow air thru the A/C condenser and keep the coolant temp from soaring.

ujmolter

Ok. I will do that to see what codes are stored.

ujmolter

I check that already and they look ok. Thanks.

ujmolter

Well I pulled the codes.
1 flash followed by 2 flashes-occurs 3 times
1 flash followed by 4 flashes-occurs 3 times
3 flashes followed by 4 flashes-occurs 3 times
Then the cycle repeats.

I looked up online and found that the first code is normal. The second: 1 flash followed by 4 flashes is the Coolant Sensor Circuit High temp. The third: 3 flashes followed by 4 flashes is the Mass Air Flow circuit.

On the two faulty items, are they modules that need replacing or is there a short somewhere in the circuit?

Getting closer to solving the problem I hope!

crowz

34 is either bad mass airflow sensor, relay issues or a vacuum leak. But sometimes other symptoms like overheating the motor can cause that code to trip. If its the only code I worry about it. When its included with other stuff I usually worry about the other stuff first, reset the computer and see if it comes back.

14 is supposed to be bad temperature sensor or wiring problems to it. Then again if you got the car hot enough it could trip that one too.