I have a 97 Mazda B2300 whose A/C-heating system goes wacky when I get above 60mph. Here's the specs:

1997 Mazda B2300
Automatic transmission
2 Wheel drive
107,000 miles

The A/C blows really cold as long as I stay away from that 60mph mark. Once I go over 60 the A/C while work occasionally but most of the time I have really hot air blowing out of the defrost vents or onto my feet. Since I don't need the heat or A/C right now I've pulled the fuse for the blower motor but I'd like to get this resolved cheaply before summer rolls around. Is it something that I can do myself? Can it be done cheaply? Does anybody know what could cause the problem?

Any help would be greatly appreciated. Thanks.

 

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I posted this in another part of this board and never got an answer so I'm going to try here too.

I have a 97 Mazda B2300 whose A/C-heating system goes wacky when I get above 60mph. Here's the specs:

1997 Mazda B2300
Automatic transmission
2 Wheel drive
107,000 miles

The A/C blows really cold as long as I stay away from that 60mph mark. Once I go over 60 the A/C while work occasionally but most of the time I have really hot air blowing out of the defrost vents or onto my feet. Since I don't need the heat or A/C right now I've pulled the fuse for the blower motor but I'd like to get this resolved cheaply before summer rolls around. Is it something that I can do myself? Can it be done cheaply? Does anybody know what could cause the problem?

Any help would be greatly appreciated. Thanks.

 

Let's confirm the problem(s) as the description and progression of the sequence of events seems somewhat illogical.

1) A/C on MAX or NORMAL, works fine up to 60MPH.

2) At 61+ MPH A/C somehow quits (???DOES THE COMPRESSOR STOP??????) and hot air (I assume this means air heated from the vehicle HVAC system and not just warm/hot outside air) comes from the defrost or floor. This happens despite the HVAC system setting STILL being on MAX or NORM A/C and COLD for the temp setting?

FWIW, the HVAC system will default to air output at the defrost if there is no vacuum to operate it. Does the system happen to blow from the deforst when you have your foot into it, such as climbing a hill or passing? On another note, have you isnpected the blend door for proper operation?

 

The key here is it is coming out the defrost vents you are losing the vacume that sets everthing in its right place. Make sure that the check valve that is in the line going to the vacume storage ball is working. And that all lines are in good shape.The default position is defrost when there is no vacume.

 

The blend door (for temp control) is operated electronically and as I noted earlier, the default air discharge is defrost. Problem descritpion/clarification is needed as the combination of a vacuum and electrical problem/failure simultaniously would be fairly unlikely. Then there is the mystery of discharging air to the floor. Then it's unknown if the compressor is running.

 

Welcome to the forum upther.

Off hand....it sounds like a vacuum problem to me.

 

Welcom - I moved your thread to the B-Series forum

 

1. That's correct. Sometimes it'll be fine beyond 60mph but that seems like a pretty average spot.

2. Correct again but it's not constant and it will randomly switch between the A/C, floor, and defrost. It's hot air from the truck and not just the outside. I'm pretty sure the compressor stops but I'd have to get out on the road and try it out so I'll get back to you on that.

3. The hot air seems to be split pretty even between the defrost and feet when my foot is on the gas. Like I said it's a pretty random thing. I gotta go out later this afternoon so I'll pay more attention and get back to you with some definate answers.

4. I'm a little slow on some terms so can you tell me where the blend door is and how to find it?

Thanks.

 

I forgot to mention that the A/C doesn't have to be on for this to happen. The switch can be in the off position and I still get hot air coming out from the defrost and feet vents.

 

You my freind have a vacum leak in your console or under your hood up close to thefire wall under the dash compartment.

 

I assume that there is no easy or cheap way to fix that is there.

 

This is starting to sound like a vacuum leak or a bad check valve in the HVAC system. As I noted earlier, the system defaults to defrost when there is no vacuum; I'm puzzled by why it goes to the floor but perhaps that occurs as the vacuum is being lost. This will be further evidenced by the system switching functions (defrost) when applying the gas, such as when climbing a hill. I will also assume that you have the heat set on warm and that the system is not mysteriously increasing the heat level by itself (ie, phantom movement of the blend door). You should carefully inspect for loose vacuum hoses under the hood for starters and move to the dash area next. I would also inspect the vacuum reservoir as I *think* they have the check valve built into them. You can easily determine this by applying vacuum to the port on the reservoir leading to the HVAC system and seeing if the reservoir itself holds vacuum.

Easy and cheap are relative terms, the time it takes to diagnose the problem is just that. If you do it yourself then of course there is no labor cost so that would be cheap. If you need a replacement vacuum reservoir due to a bad check valve, you might be able to junkyard it for $5 - 10 and a new one might be $15 - 30. I haven't priced these so I'm guessing. Cheap either way though.

 

Thanks Bill. One thing though. When the A/C shuts off and goes to the floor or defrost it's really hot air coming out even though the **** is set all the way to cool.