The Pantera Place
"Your de Tomaso Connection"
A/C Condenser Fan Relay Time Delay Drop Out
By Mike Dailey
The early Pantera A/C system uses an icing/temp control switch with a single off/on contact. On the very early cars the switch controls a single A/C relay that in turn controls both the compressor clutch and the condenser fan. The later cars have two relays, one for the clutch and one for the fan but are still controlled by the single off/on icing switch contact.
De Tomaso found early on that cycling the condenser fan off and on at the same time as the compressor could cause high pressure to build up in the system and blow an A/C hose off. De Tomaso tried a number of modifications and eventually went to a icing/temp switch with two contacts, one controlled by the evaporator temp for the compressor clutch and the other just for the condenser fan to keep it running any time that the icing/temp switch was on. Although the two contact switch solved the hose blowing off problem the condenser fan runs continually anytime that the A/C is on. Not really the best solution.
My car has the single contact icing/temp switch with a
single relay, so the first thing I did to my A/C system when I rebuilt it was to
add a high/low pressure switch to the dryer that was in series with the
icing/temp switch to keep the system from running in a high or low state.
See the modification here
As I worked on my A/C system over the years and it really started working well I started to think about a way to have the condenser fan run for a timed duration each time the icing/temp switch shut the compressor off. Working with my Pantera friends I decided to add a relay dedicated to the condenser fan that has an adjustable drop out delay. See the diagram here. Having the condenser fan continue to run after the compressor cycles off provides post cooling to the condenser, so that when the icing/temp switch cycles the compressor back on the cycle starts with pre-cooled condenser improving the cooling efficiency. The same idea could be applied to the later cars with the two contact icing/temp switch to reduce the run time of the condenser fan, but my drawing only covers the early cars.
I wanted to mount the relay near the condenser fan, so
the first step was running a #12 power wire from the fuse area, through the
console and to the wiring connecter that is next to the coolant recovery tank. I
ran the wire in the same plastic loom that I used for the high/low switch wires
and then divided the path at the firewall and then to the connector area.
Using a flatten paper clip I released the wire terminal retainer and pulled the large light blue black wire out of the back part of the connector, so that the existing wire in the wire loom going to the condenser fan area could be used.
View of the removed wire, heat shrink, and new connection
to the black power lead. The connection was taped off to seal it and the
connector and the power wire was put back in behind the recovery tank in its
View of the condenser fan time delay relay mounted near the A/C dryer. I made a mounting tab from a piece of steel strap and bonded it to the relay case with CA. I chose to put the relay near the fan rather near the existing relay rack up front to reduce the amount of wiring.
I used a special split connector to add the new black #12 fan relay power to the existing A/C fuse #7.
A diode is needed on the pick terminal of the time delay relay to prevent a feedback to ground through the compressor clutch relay coil. The time delay relay pick current is very small so I just used a diode that was large for its physical size and strength.
Connection for the time delay relay pick terminal at the high/low switch. Note on the drawing, that I placed the connection so that if the high/low switch opens the condenser fan will continue to run if the icing/temp switch is on.
Note: The power to the fuse #7 is not switched by the ignition switch. I could have added another relay to control the power, but it did not seem to be worth the extra complexity. If the A/C is left on when the key is turned off the fan runs out the time and shuts off. I currently have the relay timer set to one-half minute. It can be adjusted on the bench before installing and the adjustment is very sensitive. Here is the spec sheet on the relay.
When installing this modification on the cars with the single A/C relay there is a large anti-feedback diode and heat sink mounted on the condenser frame that can be removed from the fan power lead resulting in .6 more volts to the fan motor.