ew928

ChuckS,
Someone posted some time ago that the older (think pre 83') uses a different
A/C head that doesn't use the relay.

Been on the RadioShack relay for 1 month. Helped me do the SITM trip and
Watkins Glen race crew week after. Great to have A/C for 2200 miles of driving.

Of course I connected all 8 wires before re-reading Greg's instruction.
I placed the Radio Shack 275-249 in the original location as the Gruner.
Ran wiring from bottom side of board up to the top.


Ernest (NYC)
Waiting for the R-134 conversion to leak out as Capt. Earl predicts.

Sab

great info Greg, thanks. got the radio shack 5 amp relay and it works like new again.

Jadz928

Going in to the HVAC head for lighting udgrade. Also soon about to perform complete HVAC R&R (to include conversion to R-134).
The existing Gruner head AC switch relay is working.

Is now a good time beef up this relay, proactively? OR

Will adding a IN4007 diode protect the relay from EMF, thus preserving its use?

Secondarily, it's been recommended to add a 3amp fuse on the clutch pwr feed line, btw the CCU and relay. Is this basically performing a similar function as a diode would, in the fact the it protects the relay from a reverse EMF from the CCU?

Any help would be much appreciated! Thanks.

dr bob

Jim--

There's a "suppressor" in the CE panel that's no more than a diode in a relay case. Does what you intend for the control-head diode to do, sort of. IOf you are looking to protect the relay contacts from the reverse EMF from the clutch coil, you can add a diode across the relay contacts. Needs to be pretty beefy, maybe north of a 1 Amp rated 1N400x, since the available current is higher. But OK to start with that and see how it survives.

Adding a fuse does nothing for the reverse EMF protection; it's solely to protect the board traces and the small wiring from overcurrent damage. Greg's solution is to put it near the freeze switch. Since you have the head out, it's a toss-up for location protection vs. service access for the fuse.

On the relay replacement, I'd do it now just because it's really easy and you have the thing apart. JMO, of course.

jwillman

Chuck,

OB HVAC are way different and easier.

https://rennlist.com/forums/928-foru...ller-woes.html

Jadz928

Thanks Dr. Bob.
So what kills the relay... arcing due do EMF, overcurrent, or both?

I'm still curious if a diode would extend the relay's life indefinitely...
Along with a 3 amp fuse...

I'm comforable adding the fuse at the freeze switch, but understand it may not be the most ideal place in the circuit.
And thanks for clairfying its different purpose.

BTW, read thru your AC R&R write-ups on Nichol's site. Fanstastic!
All I have left to figure out is how best to flush the lines, once the compressor is removed, prior to breaking seals and replacing o-rings.

dr bob

Both. The arcing increases the resistance in the contact, the heat then does them in. A diode will reduce or eliminate the arcing, so might extend the life of the existing relay some. It still isn't rated for the duty, with the basic current requirements more than the contact rating. The rating is also for AC current, where the current drops to zero 120 times a second. So the contacts expect to have no more than that short period to arc before the current stops. DC has no relaxing of the current, so the arc lasts for as long as there's a suitable arc path for the voltage.

A diode will help with arcing but "extend the relay's life indefinitely..." is a stretch. Remaining life hinges on how mach arc damage has been done already. A diode won't heal existing damage.

Landseer

Expansion valve is too restricted for flush, needs to be removed. Same with dryer to get clean safe flush of condensor.