AC Heat Time Delay Relay

[LowBikeMike]

Would someone with a 69 w/factory AC be kind enough to pull the two wires from their AC time delay relay (found under the right hand trim panel at bottom of heater box)and measure the resistance between the two terminals on the relay without vacuum applied?

I'm working on putting my AC wiring back together properly and have figured out how this relay works, but mine is showing close to 75 ohms at rest, then infinite once I apply vacumm and the timer kicks out. I think the infinity reading is correct, but I don't think it should have 75 ohms to start with, I cannot find any source that gives any specs.

Thank you in advance. I would also be interested in purchasing a good used AC time delay relay for a reasonable price.

 

[Sixpactogo]

I have two of them. One reads 1.3 ohms and the other about 3 ohms. Not sure if either is right.

 

[LowBikeMike]

Thank you. That is more of what I would be expecting. Low resistance to let current pass to blower motor until it times out then an open circuit stopping current flow.

If you would like to sell one of them I would be interested.

 

[Sixpactogo]

From a little research I've done on the time delay switch, It is supposed to open after a minute or two of operating the compressor when you turn on the heat or defrost. I tested both of mine and neither one opens the switch with a vacuum of 20 inches. How did you get yours to open with a vacuum? My compressor runs constantly in defrost mode but it does shut off after a while in heat mode. I unhooked the time delay wires but mine still runs the compressor in defrost mode. It looks like the control switch I have is not the correct on for my 68 Charger since the center contacts are closed in the defrost mode and should not be. The control switch I have is pn 3895790 and is the wrong part number for our cars. My car should have Pn: 2820487 and 69-70 B bodies used pn: 3431017 control switches. Some people have said they are all the same but with superseded part numbers but that turned out to be bogus.
I did find some new Time delay switches (PN: 2837697) but they want anywhere from $100 to $295.00 for one. I really don't need my compressor to run in either heat or defrost mode since I seldom use the heat. At least your timer opens up with a vacuum applied so probably works the way it should.

 

[LowBikeMike]

It appears after fooling with my time delay relay it is working properly. I purchased a spare AC/Heat box for the heater core and it also had the relay still attached. Its broken, so I was able to dissect it a bit to get a better understanding of how it functions.

At rest the relay passes current, so power that is applied to the brown wire from the AC selector switch passes through the relay and turns on the compresssor. I may be wrong but I believe when vacuum is applied to the center nipple, the vacuum is only applied to the bi metal spring inside the relay. After a few minutes, vacuum is then routed to the hose that runs around the back side of the of relay. Now vacuum is applied to the internal portion of the valve, after a few minutes the vacuum collapses the top portion (think lid) of the valve and trips the contacts opening the circuit, shutting off the compressor.

In your case it sounds like your relay is working in the heat position because the compressor shuts off. Mine is not hooked up, in fact the wiring was all fubar and my fan motor ran all the, and the AC selector fan switch was wired around. I have hopes of reconnecting it so I checked my relay by applying vacuum to the center nipple with my ohmeter on the two relay contacts. Before and after applying initial vacuum the resistance was about 1 ohm. After a few minutes with vacuum applied I can hear an audible click and the circuit them goes open.

I'm using 2571-501 AC selector in my 69 RR and it seems to work properly for my application. I also had it recently rebuilt to address the fan issue. I only have continuty between the light and dark green wires in AC mode, not defrost as you mention. I would think you could have yours rebuilt to solve the defrost issue. I can take some pictures of the relay internals if you are interested. I'm certain I am right about how the relay opens the circuit, I am not convinced I know how it measures time or overcomes the bi metal spring to reroute the vacuum to open the circuit.

 

[Sixpactogo]

I'm sure you are correct in your speculation on how the timer works and yours is working properly. Maybe I didn't wait long enough for the vacuum to open the switch. I will have to do more testing. The service manual says "it should open in a minute or two" but the one in my Charger is more like 15 minutes. I know I have the wrong controller in my car at this time. I have a new control switch (PN 3502-126) that is not exactly correct either but it is different in that it has the center contact closed when the off button is pushed. It seems to me that that control switch would want to run the compressor anytime the ignition is on. I have not tried it as it requires dropping the steering wheel and removing the gauge panel to get at the wiring plug. Guess I will leave it along since I don't use the defrost mode anyway. Thanks for your input. The only thing I know for sure is that all of those control switches are not superseded numbers as they don't all work the same.

 

[LowBikeMike]

My center contacts only allow current to flow in the AC or Max AC mode. No current flow in Off, Heat or Defrost. Based upon the 69 Plymouth wiring diagram I am using, in Defrost and Heat the AC compressor gets power thru the Delay Relay relay via the 3 wire blower connector on the AC switch.

 

[Sixpactogo]

Yup.......That is the way it should work. PNs 2820-487, 2571-501, 3431-017 all work that way. PN: 3502-126 center contact made up in off position. PN: 3895-750 center contact made up in Defrost position. No idea what vehicle they are for.