Air Conditioning HELP

what ever you do DON'T keep that wire there you will blow the compressor up because it's getting too cold and screw all the seals in the system the "thermostat" that the guy is on about might not be the cause of your problem most of the time, these things are caused by an earthing problem with the tri-function switch next to the receiver dryer (behind the right hand headlight when you look at the front of the car) sort this out and 90% of the time this problem goes away

it could also be the fact that the receiver dryer has reached the end of it's life and the water build up in the system has overcome the refrigerant so you may need to change this

there is also a thermo switch in the actual bulkhead box (depending on right/left hand drive variants, you need to remove the windscreen scuttle, wiper motor, heater/blower box to remove this and reinsert it, but if he hasn't spotted this then he may not have been looking hard enough or had something else to do and didn't want to waste 3 hours dismantling everything just to push the wire back in again basically it tells the car how cold the air con system has got and is the equivalent of the temperature setting on your household fridge when it gets cold enough it switches the system off, when it gets hot again it turns it back on so that it cycles in and out to regulate the temperature leaving it on freezes up the pump

(guess who's been on an AC course :) ok, so it was about 4 years ago but it's still relevant)

if you have gas in it then the last possibility is that the pressure switch (the same tri-function switch as mentioned earlier) has failed but to replace this you need to top up the system again (with the temp switch you don't)

hope this helps

The Sierra A/C has only 3 switches. (1) dashboard switch, (2) Hi/Lo pressure switch (on top of Receiver Dryer), (3) Evaporator Thermostat. It has a Compressor Pump clutch of course, Fan and various relays as well.

Bypassing the Evaporator Thermostat will not initially freeze your pump but it WILL freeze the moisture that forms on the outside of the Evaporator resulting in air not being able to get into the vehicle. It would be wise to turn it off at that point! Removing the Thermostat is not too difficult as its only held in by 2 screws but it might cut your fingers up a bit as they are difficult to reach. The Thermostat on this model is not an uncommon problem. Once out you can test it in the freezer. The cut off point should be about 4 degrees.

The Hi/Lo pressure switch can be removed without needing to top up the refrigerant. Basically undo it very quickly and only a tiny amount of gas escapes. Check the wiring first but if the Hi/Lo switch is definitely giving problems I have a working spare you can have for £10 inc recorded delivery (alas I have used my spare thermostat already!).

Regards, Steve

and screw all

cause of your

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the end of

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(depending on

windscreen scuttle,

but if he

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dismantling everything

and is the

gets hot again

years ago but

pressure switch

the temp

to sort out my

I took it to

that it was 95%

sort of

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the pressure switch is there to see how much pressure there is in the system removing it and then not having to top up the system would be like removing a tyre valve and then not having to pump the tyre up again

Perhaps, the outside air temp sensor. normally fitted infront of the rad but behind the bumper area..ie out of direct air flow when car is moving.

top

in the system

like removing

Whether this is true of more modern systems I don't know but the analogy is certainly incorrect in this instance. The Sierra's (and comparable Granada R-12) Aircon system is designed to allow changing the Hi/Lo pressure switch without regassing. The switch screws into the top of the Receiver/dryer unit which incorporates a valve operated by a plunger. The final tightening of the switch depresses the plunger and releases the gas through a tiny orifice in the receiver/dryer and into the bottom of the switch. When removing the switch there is only a tiny amount of gas leakage as the shut-off valve closes on the first couple of turns.

This is an old system and doesn't use a separate air temp sensor but relies instead on the De-Ice thermostat in the evaporator. I should explain that I have a 1990 2000E fitted with this system and am quite familiar with it and its wiring. It is a basic system (good old Fords :).

The only down side to it is the confusion over the best replacement gas to use in R12 systems. I'm off for a re-gas next spring but have still to be convinced weather there really is a "drop in" mix as effective as the original R12. Different Air/Con mechanics give differing advice and there is a lot of info out there much of which is contradictory.

HTH Steve

of the rad but

moving.

to sort out my

I took it to

that it was 95%

sort of

cut in and out.

pump (with the

the car) So

thermostatic

directly to

is a

all the

do they

your analogy is correct, BUT, you forget that the gas is under such pressure that removing the switch tends to let most of the gas escape anyway :)

on a more serious note, it also may mean the loss of fingers as the refrigerant can also cause frostbite

on the sierra it doens't make that much of a difference on teh granada it makes a noticable difference (the way around it though is to fool the temp switch into thinking it's warmer than it is so that it cools the charge down further than it normally does ;) )