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Couple of questions as I try to follow the shop manual instructions for pulling the engine to replace the head gasket on my '99 STS, 9 engine

1) Where is the fuse for the SIR? The manual references a rear electrical box, but not where it is. Is pulling the fuse sufficient to disable the SIR?

2) When you pull the air cleaner assembly, do you leave the PCM attached to the engine? Or is there a plug that can be pulled to free the PCM from the car?

3) The radiator assembly has 2 heat exchangers. The "front" one has 2 lines coming into it on the passenger side, one into the top and the second into the bottom. They both run to a manifold immediatly next to the radiator where they meet 2 lines coming from the firewall and the bottom of the engine respectively. To pull the radiator do I need to separate this manifold? There are 2 bolts holding it together and I can't see any other way to free up the 2 lines feeding the front heat exchanger. I cracked one of the bolts,heard a hissing sound and closed it.

4) Where can I break into the A/C system without releasing refrigerant? The condensor is supposed to come out with the radiator, but I assume I have to separate a connection somewhere to do so?


btw - This site and forum is far and away the best i have found anywhere, and much superior to the sites I follow for my other cars.

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1. It's under the rear seat.

2. I think there is a plug.

3. I think you may be confusing the radiator and the condenser. The condenser is in front of the radiator.

4. You can't. If you open any line, you vent refrigerant. I have heard that you can leave the A/C alone. Just dismount the compressor from the mount at the block and leave it in the engine bay tied to the frame or such.

Others with experience will chime in and add to what I said or correct me if I am wrong.

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The first thing you should do to prepare for this job is to get a factory shop manual (FSM). If you don't have one, you are flying blind. You should get one and study the procedures for removing and replacing the engine, removing the manifolds and heads, etc. They are sold new by Helm, Inc. Link:


Some people have had good luck getting manuals from eBay.

The rear fuse block is behind the rear seat and is accessed through the trunk. Looking into the trunk, it's high on the left, under the velvet trunk liner. Look for a 20 A fuse marked "SIR." I'm going by my 1997 FSM, which is not for your platform, so someone with a 1999 STS FSM may jump in and correct me here.

The small radiator at the lower right of the A/C condenser is the power steering oil cooler. I would try to leave it connected and attached to the condenser, but if you must disconnect it, be prepared to drain the power steering fluid.

The PCM has a large plug on it that you can disconnect.

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I am sure that the SIR fuse is in the fuse block under the rear seat. My daughter had a '99 SLS and I had to pull that fuse when replacing a steering wheel control button.

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If the '99 is similar to the '97 model, if you pull the engine from the top, the A/C line from the accumulator to the evaporator will interfere with the engine removal.

'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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If it's similar to the '97. it should be possible to pull it from the top. The engine will need to be bumped a bit as it is pulled up so it can squeek past the AC accumulator lines.

The AC compressor can be removed and left in the engine bay. Wire it onto the front of the car so it does not fall out during engine removal.

Get a Helms manual. This will save you lots of frustration when reassembling.

Keep us posted on your progress.

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First, did you decide to pull the engine from the top or drop the cradle?

If you can move the compressor out of the way you may be able to leave the AC connected but it's easier to disconnect it and recharge it. The only issue with that is getting a vacuum pump to remove the air and moisture that gets into the system while it's opened. If you can rent or borrow gauges and a pump it's pretty easy to do.

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The GM service manuals I'm using contain the directions for dropping the cradle, so I'm going to do it that way. The manual requires you to recover the refrigerant as a first step.

I'm trying to avoid cracking into the A/C system , but to drop the engine the radiator needs to be removed, and I don't see a way to get the radiator out without venting refrigerant. The manual treats the radiator and condeser as one assembly.


Also - The directions for removing the radiator instruct you to disconnect the transmission cooler lines. What type of fitting are these? Just loosen with a wrench/ratchet, or is a there a spring clip?


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....Also - The directions for removing the radiator instruct you to disconnect the transmission cooler lines. What type of fitting are these? Just loosen with a wrench/ratchet, or is a there a spring clip?

You could remove the fitting from the end tank with a wrench BUT there is a spring clip that might be protected by a nylon/plastic collar. After the plumbing is loose, slip the clip back on the fitting so you don't lose the (small) clip.


Drive your car.

Use your cell phone.


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I have the equipment to service AC so opening it wasn't a problem. I have a relative that has a shop and he recovers the freon if there's enough.

It's R134 so not very valuable. If you have someone recover it you'll have to tow the car to their shop and probably pay them.

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You can get yourself a vacuum pump real cheap.

Find someone in your neighborhood who services window air conditioners. He'll have a pile of old machines behind his shop; many will have good compressors.

Buy him a Coke and a slice of pizza and ask if you can have one of those junk machines that has a good compressor (he'd otherwise have to pay to have it taken away).

Remove the compressor from the A/C and connect 110 volts AC to it.

Braze a fitting on the suction side of the compressor and connect your refrigerant hose to it. PRESTO! Vacuum pump. No charge (almost).



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