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This is the electrical diagram for the A/C system (C60 option code) taken from the 1982 Corvette shop manual. I see one relay drawing/symbol and its the firewall mounted blower motor relay that you already tested. Perhaps you could share the source for the "blocking relay" mention from the internet? Remember they made the C3 Corvette from 1968-1982 and the A/C system design changed quite a bit during those 14 years. The later-1977-82 use a CCOT system.
I googled the question "Does a 1982 corvette have an A/C blocking relay?" and got this answer. I do not know how accurate it is. Older Corvettes (like 1971) did have a blocking relay.
Yes, a 1982 Corvette does have an A/C blocking relay, also sometimes called a "blower motor cutout relay," which is designed to temporarily cut off power to the A/C blower motor in certain situations, like when the engine is cranking or during high electrical load conditions; this relay is typically located near the A/C unit behind the firewall.
Key points about the A/C blocking relay in a 1982 Corvette:
Function: Prevents the A/C blower motor from drawing excessive power during engine start-up or when other electrical systems are heavily loaded.
Location: Usually found on the A/C unit itself, behind the firewall.
Troubleshooting: If your A/C blower motor doesn't work properly, checking the A/C blocking relay should be part of your diagnostic process.
And checking further I now believe that this blocking relay was actually the anti-dieseling relay used on early 1970 cars.
I am still fighting the issue of the blower motor coming on when the blower motor is grounded, EVEN WHEN THE KEY IS OFF.
I just today discovered that the diode on the A/C clutch connector was broken so I have to replace it before I can continue to research the blower motor mess. What a pain in the azz this blower motor issue is.
Does the red wire on the relay have power to it when the key is OFF on a 1982 Corvette?
The red wire at the hi/blow relay connects to the starter. It has 12volts at all times.
The orange wire at the hi/blow relay gets 12volts when the A/C blower switch is placed in "Hi" position.
In "Hi" position the orange wire energizes the coil in the relay and the contacts move to close the circuit for 12volts from the starter (red wire) to travel thru the purple wire (at the relay) to the blower motor. When not in "Hi" position the dk blue wire feeds 12volts from the blower resistor to the hi/blow relay. The blower resistor has various resistors inside that are fed from the blower speed switch at the centre console (low/med low/med hi/hi).
Here is a schematic that helps explain it. I converted my car to a more modern style wiring system, that's why there are notes on the schematic.
Note that the ground (black) wire at the blower motor was sized incorrectly from the factory. It should be replaced with a 12ga wire. The red wire from the starter motor is 12ga. This 12ga red wire feeds the current directly to the blower motor in Hi fan speed switch setting (when the hi/blow relay is energized).
If the blower motor is running with the key off I would bet that the 5 pin hi/blow relay is bad. Note where the red wire and the purple wire attach to the relay. Disconnect the electrical connector then use an ohmmeter across red and purple wire spade terminals on the relay. If the reading is infinite/blinking- it's working normal. If it reads zero than the contacts have welded in the closed position. If this is the case then you have found your problem. Replace the relay.
I still recommend upgrading the ground wire at the blower motor. It should be a 12gauge wire. Unfortunately it's not easy to get to.
If the blower motor is running with the key off I would bet that the 5 pin hi/blow relay is bad. Note where the red wire and the purple wire attach to the relay. Disconnect the electrical connector then use an ohmmeter across red and purple wire spade terminals on the relay. If the reading is infinite/blinking- it's working normal. If it reads zero than the contacts have welded in the closed position. If this is the case then you have found your problem. Replace the relay.
I still recommend upgrading the ground wire at the blower motor. It should be a 12gauge wire. Unfortunately it's not easy to get to.
I have tested and replaced the relay. I have also added an upgraded ground wire to the blower motor.
I still cannot understand why EVERY single wire in both the relay (5 wires) and the resistor (4 wires) all have 11.90 volts when the blower motor is grounded. It makes no sense.
I have tested and replaced the relay. I have also added an upgraded ground wire to the blower motor.
I still cannot understand why EVERY single wire in both the relay (5 wires) and the resistor (4 wires) all have 11.90 volts when the blower motor is grounded. It makes no sense.
Using the line diagram above the Red wire (Circuit #2) is HOT at all times when the battery is connected. Circuit #2 lands on a normally open contact of the High Speed blower relay. You either have a wire landing in the wrong connector cell of the blower relay or a defective relay.
I have tested and replaced the relay. I have also added an upgraded ground wire to the blower motor.
I still cannot understand why EVERY single wire in both the relay (5 wires) and the resistor (4 wires) all have 11.90 volts when the blower motor is grounded. It makes no sense.
Sounds like the red wire is shorted to the dk blue wire. It's back feeding. With the key "off" that's the only way you can be getting 12 volts to all those terminals you mentioned.
Inspect the interaction of the red and dk blue wires at the area of the hi/blow relay connector. What usually happens is the insulation melts back at the connector due to engine heat over the years. This picture shows an example of that.
A/C Blocking Relay on 1982 Corvette
