Hi!

My '89 Ebay rat runs perfectly with one odd exception related to the air conditioner which I have had since I rescued the car from its previous owner. When I use the air conditioner and the car is stuck in traffic, the temperature will ultimately creep into the upper 220 range, notwitshtanding the fact that the cooling system is in top notch condition, both fans are running etc. (I usually shut it off before that point). Yet, when I am moving along the temperature drops into the mid to high 180s with the air on. Without the air on the car runs in the low 180s, high 170s traffic/no traffic---GREAT. I have noticed that the air conditioner compressor clutch is not cycling/engaging on and off, but that the compressor runs continuously with the air on. This leads me to wonder whether that could be the source of the unusual temperature variance with the air on and the car stopped. Has anyone had a similar problem? I will replace the cycling switch in any event, but wanted to ask first.

Keep on surging!
/s/ Chris

 

.....pretty much normal....as when you are moving the volume of air over the cooling system and condensor increases...while standing still or stuck in traffic, all is reduced and thusly higher temps.....

 

Sounds normal. The fan does not go on unless the temp hits 226-228 degrees or the a/c is turned on. One way to ease the temps under the hood is to make sure the radiator air intake is clean of debris and the radiator is also clean. A flushing of the system is not a bad idea, and you can clean the radiator with simple green to get the road dirt off of the radiator (allows better heat loss). and reach into the air intake and get the crud out. Another way is to pull the radiator, not a difficult job, clean it, including the surrounding areas of the engine compartment and a/c condensor. If you have an automatic, remove the transmission connections. You will loose only a slight amount of fluid that can be easily replaced.

Flushing the system does a good job with lowering engine temps. In addition, check your serpentine belt to make sure it is not too old and shiney.

 

1. the temp thing is normal. the fans should come on about 223, and turn off about 215....or close to that.
2. if the A/C is selected to 60 degrees, the A/C is the same as a regular ol GM car, in that in the lowest seting, the fan motor revs a little higher, the recycle door is open, and the outside air is shut off.
The compressor cycling is stopped, and it runs continuously until the A/C selector is moved off the lowest selection possible.

 

Thanks, everyone!

That's interesting about the cycling feature being shut off at the lowest setting---I will try it out!

Cheers,

/s/ Chris

 

First, only one fan should be running - Aux fan is not used for a/c (and it should allmost never come on anyway - plenty of Vettes left the Factory without it).

The ECM uses a signal from the high pressure side of the a/c system to ground the main fan relay. A switch, on that line, opens at 230 psi, and the voltage rise at the ECM tells it to ground the Relay. That switch recloses at 190 psi, at which point ground is removed from the relay and the fan should turn off. Pressure is heat and it is dependent upon the outside air temp - high temps - higher pressures - so if it's 90 degrees or better, the fan is going to be running anytime the vehicle isn't moving. Ditto for your compressor - the cycling switch cuts power whenever the pressure is low enough to freeze over the Evaporator. The lower the outside temp, the lower the pressure/temp of the fluid being metered into the core. If it's 70 or above, the low side shouldn't be dropping to the cutoff threshold so the compressor will always be cranking.

As to operating temps, the more that coolant fan runs, the lower the temp at the radiator and in general, a/c turns that fan on a lot sooner and runs it a lot longer than if it were off.

Every car I've owned runs cooler with the a/c on - my '89 about 205 to 212 - and having owned it since it was new, I know that's how it rolled off the Dealer's lot. Should I turn off the a/c, it'll climb to 226 and then cool to 217/220 before cycling the fan back off and repeating the process, so I gain a couple of degrees with the a/c on.

Yours looks close to spec, but I'd be curious as to why both fans are running. In fact, my experience with running both (I had to try it back in '90 as it was the "hot thing" to do), is that it simply overwhelms the alternator and as the voltage drops, the fans slow down. And that causes the coolant temp to creep up at idle (along with the temp of the air out of the vents). I'd try yours with just the one fan and see if it doesn't gain a few degrees or if not, keep an eye on system voltage as dropping below battery can also cause driveability issues.

 

Thanks! The reason both fans come in is that I have them wired to come on together with one of those low temperature switches installed. What I like about the arrangement is that (except when the air is on), the temperature stays in a very narrow and comfortable range. I don't like temperature cycling up and down continually in a wide range, though I have seen it said repeatedly that it doesn't really hurt anything. It's worked great for about 2 years, and the only weird thing is why the air conditioner causes it to rise so much. I will set the temperature tonight to trigger the cycling of the compressor, and see if that helps. I appreciate your kind and lengthy reply /s/ Chris

 

I'd guess - per my own experience - your alternator isn't keeping up. The last time someone put a clampon meter on one, they got about 25 maybe 30 amps at idle. The Blower Motor, on high, can draw 25 amps. Both fans, easily another 10 to 15. Add in the radio, brake lights and an 18 year old harness, you're on battery and dropping. Fans slowdown, temps creep up. Later Years upped the ante and went with a 140 amp alternator, though I haven't seen a post or test showing the difference at idle. They also use a more efficient fan motor with both in the air stream for cooling. You might also make sure that your Blower Motor is being cooled. Should be a hose from the housing to the motor. Check the connector/harness too for discoloration which means it's heating up - usually because the connectors are loose. If so, take apart the weatherpak and solder the terminals to the wires.

 

Thanks! I'll do some additional experimenting as you suggest.
/s/ Chris