[cj1]

Times it doesn’t start try adding fuel to intake(starter fluid spray) just to see if lacks fuel.

[cj1]

Check the a/c idle-up valve/hoses. Turning a/c on should energize valve. Since its connected to vacuum hoses it may be opening up vacuum leak which in turn causes IAC to compensate.

If you measured 6v across the ac fan when a/c on then the other 6v would be across the rad fan.

[cj1]

If disconnecting the clutch and pressure switch drops out the clutch as expected, then check that the hot/cold valve is fully closing off heater water.
Possible that an elevated evap temp, above 37 degrees, due to heater not closing off entirely.
Other possibilities are thermostat not working, condenser debris,condenser fan, air/water in system.

Since it is an older system and if hasn’t been serviced best to have it evacuated, hold vacuum/leak test and recharged to specs.

[cj1]

Something you can do without using meter.
With clutch engaged momentarily disconnect its connector, clutch should drop out.
With clutch engaged momentarily disconnect the pressure switch, clutch should drop out.

Regarding the pressure switch effect on the compressor clutch. That switch is normally closed until a extremely high maybe 450 psi or low below 32 psi opens it and interrupts power to compressor clutch relay.
Go slow on changing out the pressure switch.

[cj1]

Take a look at BBBind.com for the schematic. Believe A/C thermostat controls compressor cycling.

[cj1]

Tests you can do quickly at home;
1. Monitor bat voltage at idle all electrical accessory turned off. Compare to voltage at 2000 RPM all accessory turned on.
Is the voltage always between 14-15v as you suggest?

[cj1]

Pressure test just to eliminate possible leak.

Can you access a scan tool to get the actual temp of the ECT. Would also be useful to see live data to verify normal engine parameters such as operation of fans in relation to ECT.

For clarification, radiator was replaced a year ago because of same overheat problem?

[cj1]

Pressure test the coolant system only way to see if losing pressure. Don’t forget to test the cap.
What type of combustion gas test did you do?

[cj1]

Test for combustion gas in coolant. Pressure test coolant system. Both cheap and easily done.

[cj1]

Slight overheating problem. Best to monitor the engine temp with a scan tool. The dash may not reflect actual ECT.
Verify that fans come on when ECT reaches say around 215, which probably is the upper end operating temp.

[cj1]

Sounds like a plan.
If head gasket is breached from coolant passage to combustion chamber that may show up in a pressure test of the coolant system.
Regarding combustion gas test, auto parts store should have chemical test kit to loan.

[cj1]

Verify that the coolant system can hold at least 16 psi., Maybe but some trace dye in and pump it up to 18psi let it set will you check for leaks. Also check that the cap is holding at rated pressure.

At 16psi coolant can reach 270F before boiling but at 8 psi will boil at 250F

[cj1]

ABS may be energizing, can you feel a brake pedal movement/noise?

[cj1]

“Forgot to mention that I put the 192 degrees OEM thermostat and a new rubber ring around it (the old ring was cracked and swollen).”
The cracked ring would allow coolant to bypass the thermostat. This would account for the low/erratic temp readings thus erratic fan operation.

[cj1]

‘Also, I’ve recently noticed that sometimes when the engine’s hot and I rev it the lower rad hose collapses, then restores when I release the throttle’
Looks like hose needs replacing.

[Author]

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