cjmspartans
OBS Enthusiast
With the temperatures hitting mid to upper 90s almost daily now, I threw in the towel and decided to start poking around with my 97 Suburbans (7.4L, no rear A/C) air conditioning system. It hasn't worked at all in the 4 years that I've owned it.
To start, I tested the clutch on the compressor and it spins freely. No problems there... so, just to see if it'd work I threw in four cans of r134a (4lbs, no stop leak garbage, sticker on the receiver drier calls for 4.4lb charge) while jumping the compressor where the relay would normally be installed. Pressure on the low side with the compressor running was roughly 50psi with the outdoor ambient temperature of 90 degrees.
Now, with the system appearing to be charged up, it would blow cool air (not super cold, system has a known leak and I didn't fully evacuate it when it was at atmospheric pressure) when I had bypassed the relay. When I reinstalled the relay, the A/C clutch would not engage at all.
Things I have done:
Any ideas of what I should look for and next steps to figure out why the compressor won't engage with the relay? I would get the system evacuated, change the orifice tube and the receiver drier, then recharge with UV dye but if there's an electrical issue I'd rather tackle that instead of putting the cart before the horse.
Thanks everyone!
To start, I tested the clutch on the compressor and it spins freely. No problems there... so, just to see if it'd work I threw in four cans of r134a (4lbs, no stop leak garbage, sticker on the receiver drier calls for 4.4lb charge) while jumping the compressor where the relay would normally be installed. Pressure on the low side with the compressor running was roughly 50psi with the outdoor ambient temperature of 90 degrees.
Now, with the system appearing to be charged up, it would blow cool air (not super cold, system has a known leak and I didn't fully evacuate it when it was at atmospheric pressure) when I had bypassed the relay. When I reinstalled the relay, the A/C clutch would not engage at all.
Things I have done:
- Checked the high pressure switch. The switch is open; there is no continuity on the switch its self, and when I jump the connector on the wiring harness with a multimeter, I get 0.003A of current and the electric cooling fans turn on.
- Checked the low pressure switch. When I jump the wiring harness connector with a piece of wire, there was no change. The compressor clutch still wouldn't engage.
- Attempted to backprobe the low pressure switch with my multimeter to detect current. Couldn't detect any current, but I also don't think there was a good connection.
- Measured current at the 10A A/C fuse in the fuse box under the hood. When I bypass the relay to engage the compressor clutch, this fuse reads 0 amps which seems... unusual. This fuse always reads 0A, clutch engaged or not, HVAC controller in the dash set to max A/C or no A/C.
- Current of the compressor is ~3.5A when I used my multimeter in place of the relay. Seems on par with my Ford Bronco's R12 compressor, and sounds healthy.
- Swapped relay with a known working relay.
- Measured ~13V across the two pins on the relay that energizes the electromagnetic coil to close the high current side of the relay. It is always reading ~13 volts, with the HVAC controller in the truck set to max A/C, A/C and having A/C turned off as well as the blower motor turned off. This seems unusual to me as I'd expect no voltage when the HVAC controller is not calling for A/C,
Any ideas of what I should look for and next steps to figure out why the compressor won't engage with the relay? I would get the system evacuated, change the orifice tube and the receiver drier, then recharge with UV dye but if there's an electrical issue I'd rather tackle that instead of putting the cart before the horse.
Thanks everyone!
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