A/C compressor tired -> no low speed fan at idle?
 

Hi everybody
I have just replaced a leaking evaporator. I have also replaced drier/accumulator including pressure switches and all O-rings.
Then I charged by weight, with R12. I realized that the pressure I got was relatively high on the low side (around 45 psi) and quite low on the high side (190-210psi). So in heavy traffic the auxillary fans are not triggered by the pressure switch, only when the engine revs up the fans are cutting in.
Also I keep reading that the coolant temp sensor triggers the fans at 105 C? Mine (car is 300TE from 1992) does not, but seems to function as an emergency switch to disengage compressor and enagage fans at 130C.
My questions:
- Is my compressor on its way out? Can I wait or shall I replace it now (danger of sudden "black" death)?
- Is there a trick to make the fans kick in earlier (at low speed), say at 100C? Would that cool harness be a solution?
Many thanks for yoou rcomments!
Bruno

Are you sure the low speed fan isn't coming on when you turn on the A/C?

If the fan does not come on, perhaps your resistor is bad - I just had to replace mine, after having fixed the wire to it twice (they like to melt).

The low speed fan does come on, but only when the compressor runs at higher speed (> 2000rpm). Resistor is new and wire is ok (measured <0.3 Ohm). Also, low speed fan comes on when I short the wires to the pressure switch.
So, it must be a weak ccompressor?!
Thanks, Bruno

Ok
 

I found in the manual that the coolant sensor indeed should sense both 105 and 130 C. I'll replace mine because there is no reponse at 105 C and leave the compressor alone.
Bruno

Check eyesight glass for refrigerant level.
You will not get low fan unless the ambient temps are high. { High termal load].. you also will not get a low fan if the idle drops, even if you have a full charge.

No more overheating
 

after replacement of the coolant sensor. Now the fans kick in at 105 deg C.
Charge is full, maybe is just not hot enough in Boston (temperatures are currently in the low seventies) for the pressure switch at the receiver/drier to trigger the low speed fan at idle?
Thanks, Bruno

If the eye-sight glass show no bubbles, the system is full.
The thing to remember on the low fan is that by design it only comes on when the system is taxed... meaning a high thermal load. If ambients are not high , it is not supposed to come on. The only way to be sure is to use a gauge on the high side and see if the pressure sw is tripping at the design spec... [ which may not even get reached on a low ambient condition at idle]
I would take a look on a hot/humid day before worring about it.
You can change the cut-in spec on the CTS to drop it to around 100C by bridging it with a resistor [ metal film, approx 1200ohm ]
Cost about $1.
Another easy mod guys do is to jumper the high pressure sw with a cabin switch so the driver can get a fan on the radiator anytime he wants it... this helps if one knows he is going to be in traffic or is towing , etc. The concept is to get a jump on temp rise before it happens, as that is when it gets away from you............this set -up still leaves the systems sensors in auto circuit, while letting the driver over-ride them manually. Can come in handy .........