Hi Guys,

It's about 100 degrees out here in the Netherlands right now, Yes, that doesn't happen to often, but now I have problems with the a/c while I need it!!

My car is an 1986 with the AUX fan option installed. If I put the A/C on after I started the car, the main fan doesn't come on immediatly, I thought it should? Then when I'm driving, the compressor cycles on and off for about 15 minutes with intervals of a few minutes. So it gets cool... and then it gets hot again, then it gets cool etc etc. After the 15 minutes it starts working properly and then it stays cool inside.
If I then look outside, the main fan is working at that time. The car has just been recharched 2 days ago. Anybody an idea what the problem could be?

Oh by the way, I got the manually controlled A/C system...

THANX!
Raymond

 

Check condensor for debris and dirt.
Fan won't come on till high pressure switch lets it. Could be a problem with one of the switches in the ac system.
I can email you the diagnostics from my 86 manual.

 

Email is sent

 

Thanx for the mail,

If I read the diagnostics carefully, it says the ECM will turn on the FAN and put the idle rpm a little higher once you turn the compressor/ A/C on. And that's not happening in my car...... strange ehh?

Greetz

 

Anybody else any ideas???

 

Did you do the diagnostic tests from the info I sent you. There is step by step diagnostics to hopefully point out the part(s) that need fixing. A digital volt meter should be able to handle most of the diagnostics.

 

The main fan - as long as the ECM is getting an a/c request signal - is controlled by a switch on the high pressure line next to the high pressure cutoff switch. It opens when the high side pressure gets to 230 psi and the ECM sees this open circuit as a signal to ground the main fan relay, turning on the fan. As the air across the condensor cools the charge, the pressure drops and when it gets to about 170 psi, the switch closes and the completed circuit signals the ECM to unground the relay.

Disconnecting the switch is the same as an open circuit, so if you do that, the fan should come on. (To determine which one is the fan switch, disconnect each switch on the high pressure or smaller line from the condensor to the evaporator case - the one that turns on the fan is the one you want - plug the other one back in)

If it's 100 degrees across the condensor, a fully charged a/c system isn't going to drop below the 170 psi threshold. If it's below 70 degrees, the pressure will rise and fall and the fan will cycle on and off. So, if your fan isn't staying on at idle on 100 degree day, that's a clue that the a/c system may need more gas - there isn't enough in it to maintain sufficient pressure for the fan to operate.

Another clue, is that the a/c is cycling off. The a/c circuit is from the fuse to the control panel, out to the low pressure switch, on to the high pressure switch, on to the compressor, and then to ground. The switches have to stay closed in order for the compressor to operate.

The low pressure switch opens at 25 psi, a pressure it shouldn't see if it's fully charged on a 100 degree day, so if it's opening and cutting off the circuit, that's another sign the system needs gas. You can check it, by backprobing the harness with a voltimeter or checking for continuity across the switch terminals.

The high pressure switch opens at 430 psi. Regardless of temperature, a plugged up system or a fan that isn't working or a condensor that is blocked with debris (even with the fan working) can reach this pressure really fast, so the compressor turns off. Once it's off, the pressure will fall and once below the fan switch threshhold, the fan is going to turn off too. Do not jumper this switch to see if the a/c stays on as the pressures can get high enough to blow it up (and you with it). Simply see if there's continuity across the switch when the compressor cycles off. If none, you've got a high pressure problem.

As mentioned, you can disconnect the fan switch and the fan should come on. If it doesn't, the wire from the ECM is touching ground somewhere or the ECM is shot. If the compressor happens to run as long as the fan is on, that probably means that the switch is shot, and with no fan, the high pressure switch opens and shuts off the compressor.

Other than these tests, the better way to diagnose it is with a manifold gage set. That will give you the pressures and allow to determine if the system is undercharged, plugged up or if the fan switch is opening when the high side is 230 psi.

 

[QUOTE=SunCr]The main fan - as long as the ECM is getting an a/c request signal - is controlled by a switch on the high pressure line next
etc. etc. etc etc. QUOTE]



SunCr, I could write a complete AC manual with all the valuable info you post on this forum.

Jim

 

Yeah Suncr, incredible.... thanx a lot!!!

My system was filled with some fluor stuff last time, so I could check for leaks. Last week I checkit with an UV-light and YEP, below the compressor there was the very bright fluor stuff.... So... my Compressor is leaking...:-(

I'm now thinking of replacing it with a remanufactured one from ZIP-corvette together with a new condenser-dryer and an R-134 conversion kit. This way I can filled it up with 134 next time, cause R-12 is really banned here in the Netherlands...:-(

Thanks for all the input guys!!
Greetz Raymond