Relay A/C Blower or Relay A/C clutch

[Istvan]

Dear All,

I would need some help for my 72 Newport custom A/C System debug. I have the standard A/C System in my car(w/o ATC). During the long years and several owners some homemade solution was made in the A/C Control Circuit. First, they used a worng vacuum switch and did electrical by-passes of the vacuum switch. So, I investigated and identified the connections. Only one thing that is still missing is the A/C blower relay. On the circuit, see attached picture, there is a A/C blower relay. I have not found it in the car yet. Where should it be exactly in the car? I have not removed the A/C and hater unit yet, may be that is the reason why I have not found it yet.
Other question is that in the part catalog, I find two relays, see the picture. One is referring to the Blower other one to the A/C clutch, however on the circuit the relay is called A/C blower but operates the A/C compressor clutch as well. The two relays looks different in the number of connection. Based on the prats list both of the relays part of the car (or not, I do not know), but I am not sure in this. In all circuit diagram I saw, only one, the A/C blower relay was showed, I never saw the A/C clutch relay. Dose any of you have experience and could hely to figure out which relay that should be in the car and where, I need to look for? I want to set back the original circuit.

 

[CBODY67]

The 1972 factory a/c system has one quirk they might have been trying to circumvent. That the a/c compressor runs ALL of the time, even with the OFF button pushed. And the fan runs at a very slow speed at that time, too. Not what is expected when the OFF button is pushed. All factory designs, as I found out when our '72 Newport was new.

The intent of that system design, as I later read, is to keep the windshield from suddenly fogging up in cold weather, when the fan first comes on, from residual moisture which can be in the hvac case. So, run the a/c compressor to decrease that initial burst of humidity to the inside of the windshield and run the fan at a very slow speed to keep the air moving in the system.

NOW, there IS an easy work-around for these things, which I discovered.

If you move the HEAT lever toward the hot side of things, about 1/2 way you should hear a slight click and related feel in the lever. That is a switch that turns off the compressor. It is in the cable linkage that the lever runs. Which also means the heat cable is a two-piece affair, rather than one long cable. SO, move the lever to just after the click, then go to the water valve under the hood and manually close the water valve on the new cable position. Done. Just looks "different" on the inside. The thermostatic switch to turn the compressor off when temps are below 32* F still works.

The blower motor relay might also only work on the highest fan speed. To minimize current flow through the fan switch at that time. Otherwise, three relays would be needed.

In general, the hvac harness is separate from the main harness which supplies it. One section of it will be behind the instrument panel. The other side of it will be under the hood. This might help in seeing what they might have done. Yet re-wiring, or verifying the factory wiring, will probably be necessary. Might need to remove the radio for more space behind the instrument panel? Front seat removal might help, too?

Perhaps the use of relays was done to provide a degree of wiring protection to keep the current running through the fan switch lower, etc.?

AT www.mymopar.com, free downloads of the Chrysler Factory Service Manual (which might add some details of the system and how it works), as well as the Chrysler MasterTech technicial training system videos.

While you are under the instrument panel, to cover the hvac air duct joints to ensure that all air goes through the ducts with no leaks. Additionally, inspect the rh frt footwell for any rust issues, as the hvac case can be prone to leaks.

Please keep us posted on your progress.
CBODY67

 

[Istvan]

The 1972 factory a/c system has one quirk they might have been trying to circumvent. That the a/c compressor runs ALL of the time, even with the OFF button pushed. And the fan runs at a very slow speed at that time, too. Not what is expected when the OFF button is pushed. All factory designs, as I found out when our '72 Newport was new.

The intent of that system design, as I later read, is to keep the windshield from suddenly fogging up in cold weather, when the fan first comes on, from residual moisture which can be in the hvac case. So, run the a/c compressor to decrease that initial burst of humidity to the inside of the windshield and run the fan at a very slow speed to keep the air moving in the system.

NOW, there IS an easy work-around for these things, which I discovered.

If you move the HEAT lever toward the hot side of things, about 1/2 way you should hear a slight click and related feel in the lever. That is a switch that turns off the compressor. It is in the cable linkage that the lever runs. Which also means the heat cable is a two-piece affair, rather than one long cable. SO, move the lever to just after the click, then go to the water valve under the hood and manually close the water valve on the new cable position. Done. Just looks "different" on the inside. The thermostatic switch to turn the compressor off when temps are below 32* F still works.

The blower motor relay might also only work on the highest fan speed. To minimize current flow through the fan switch at that time. Otherwise, three relays would be needed.

In general, the hvac harness is separate from the main harness which supplies it. One section of it will be behind the instrument panel. The other side of it will be under the hood. This might help in seeing what they might have done. Yet re-wiring, or verifying the factory wiring, will probably be necessary. Might need to remove the radio for more space behind the instrument panel? Front seat removal might help, too?

Perhaps the use of relays was done to provide a degree of wiring protection to keep the current running through the fan switch lower, etc.?

AT www.mymopar.com, free downloads of the Chrysler Factory Service Manual (which might add some details of the system and how it works), as well as the Chrysler MasterTech technicial training system videos.

While you are under the instrument panel, to cover the hvac air duct joints to ensure that all air goes through the ducts with no leaks. Additionally, inspect the rh frt footwell for any rust issues, as the hvac case can be prone to leaks.

Please keep us posted on your progress.
CBODY67

Thanks for the details and the describe of the operaion of the system It helps to undorstand the circuit! I removed the instrumentpanel, the radio and the glovebox as well. I realized that the heater cable was broken and a hand adjuster was installed in the glovebox, I think, it was a throtel arm from a lawnmover. So I need to order a new cable. Honestly the complete A/C system is not working, the blower and the qvacuum actuators as well. I figured out the vacuum line from the engine is ok. I will check the fan when I directly connect to the battery. Jut as I said the vacuum switch is a different PN, I have already ordered the good one. So, I overviewed the cables and wires, I found some wrong or homemade connections, but the factory harnesses are fine and I can set it back to the factory version based on electrical diagram. I am worry about the blower relay, because I have not found yet. It should be somewhere under dash. Do you know where it should be underground the dash? I am afraid it is missing or removed.

 

[CBODY67]

In some cases, the relay could be near the blower motor resistor, which is always bolted to the hvac case, somewhere, so the resistor coils can be cooled by the air moving through the hvac case. These are generalities, though.

 

[Istvan]

In some cases, the relay could be near the blower motor resistor, which is always bolted to the hvac case, somewhere, so the resistor coils can be cooled by the air moving through the hvac case. These are generalities, though.

I Will check. I found the resistor, so somewhere there I look under the dash.