[DML] Re: Question about Air Conditioning cycling

["Harold McElraft" <hmcelraft@xxxxxxx>]

I see numerous responses to your concern. The one thing you should 
definitely be concerned with is the frequent cycling of the cooling 
fans. This could lead to an over heated fan circuit stopping the 
fans and causing engine over heating.

Unfortunately the fans are designed OEM to cycle precisely with the 
AC compressor. I say unfortunately because if the AC system does 
become low charged or develop another issue to cause rapid cycling 
of the compressor, the fans will rapid cycle too when you have the 
AC on. The cycle of the fans with the AC compressor is completely 
independent of the otterstat used for engine cooling although the 
fan circuits for both are integrated starting at the circuit breaker.

The fans are what I would call "utility" quality. They are designed 
to work in extreme conditions - to do this, their design is anything 
but efficient. To start each fan requires 20 amps + or - a few 
depending on the condition of the fans and the electrical system 
connections, grounds, etc. This compares to 11 to 14 amps to run 
each fan once started. As the saying goes - "you do the math". The 
constant starting of the fans is extremely hard on all components of 
the circuit and soon leads to a failure of the weakest part in the 
circuit - usually the OEM circuit breaker (a 35A standard duty 
circuit breaker with "pressed" connections) or the OEM blue module 
(notorious for poor quality inside) or the single relay (20/30 amp 
rated ? that means 30 amps start 20 run). If you beef up one thing, 
another component will soon fail ? maybe in flames. BTW the motor 
will be the last thing to go in my experience.

All of this has been the topic of discussion ever since the DeLorean 
was introduced. As new in Houston (where I started 1982), a daily 
driver soon experienced "fan fail" and eventually, virtually 
everyone did.

So, what to do? My suggestion is have the AC shop do a full service 
on the AC system including replacement of the orifice tube and 
accumulator. Alternatively, as a minimum, have them do an evacuation 
and refill with the proper amount of gas (say 2 to 2.25lb of 134 
gas ? AZ 2 lb NJ 2.25 ? just my approach). A proper functioning AC 
system will cause minimum cycling of the AC compressor and therefore 
the least amount of stress on the cooling fan circuit. I still use R-
12 (2.25 ? 2.5 lbs of gas)

Next, get one of the vendors' fixes for the cooling fans. Zilla is 
by far the best vendor package offered in my opinion ? I have no 
idea if you can still get one. Or, get Hervey's set up from SpecialT?
 the Dual 2X2. Or, install the DPNW modification (the least 
expensive but effective). I'm not a big fan of the wire jumper 
modification unless you replace the under-rated relay (Hervey may 
still have the higher rated ones ? 30/40).

Last, be sure all connections for the fan circuit are checked and 
clean ? especially the grounds attached to the frame on the front.

Another BTW - the rapid cycling is usually an indicator of low gas 
or a restricted system (probably at the orifice tube). Normal 
minimum cycling on a cool day is probably off and on every 5-10 
seconds - on a hot day cycling could range from 30 seconds to 
rarely. To get an AC system to function correctly takes the correct 
tools and a knowledgeable technician with the correct specs.

Harold McElraft - 3354



--- In dmcnews@xxxxxxxxxxxxxxx, "sweetp01569" <paul.sweet@...> wrote:
>
> While my car was in getting lowering springs and shocks done, I 
asked 
> the mechanic to check out the AC.  He said it seemed to work fine. 
it 
> blows cold air and is not leaking anywhere.  However, the constant 
> cycling of the cooling fans worries me.  The fans will stay on for 
only 
> two seconds, and off for about 5 seconds, on and off on and off.  
> Wouldn't this cause excessive wear on the fans to energize them 
every 5 
> seconds, and they only stay on for 2 seconds?  It doesn't seem 
right.  
> The cycle tiem seemed to be longer last year when I had it charged 
in 
> August.  I have the R134 conversion.
> 
> Thanks,
> 
> Paul
>









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